Adaptive Cell-mediated Immunity

Overview

Immune system Immune system The body’s defense mechanism against foreign organisms or substances and deviant native cells. It includes the humoral immune response and the cell-mediated response and consists of a complex of interrelated cellular, molecular, and genetic components. Primary Lymphatic Organs definition

The immune system Immune system The body’s defense mechanism against foreign organisms or substances and deviant native cells. It includes the humoral immune response and the cell-mediated response and consists of a complex of interrelated cellular, molecular, and genetic components. Primary Lymphatic Organs provides defense (immunity) against invading pathogens ranging from viruses Viruses Minute infectious agents whose genomes are composed of DNA or RNA, but not both. They are characterized by a lack of independent metabolism and the inability to replicate outside living host cells. Virology to parasites. Components are interconnected by blood and the lymphatic circulation Circulation The movement of the blood as it is pumped through the cardiovascular system. ABCDE Assessment.

Two lines of overlapping defense:

• Innate immunity Innate immunity The capacity of a normal organism to remain unaffected by microorganisms and their toxins. It results from the presence of naturally occurring anti-infective agents, constitutional factors such as body temperature and immediate acting immune cells such as natural killer cells. Innate Immunity: Phagocytes and Antigen Presentation (nonspecific) 
• Adaptive immunity (based on specific antigen Antigen Substances that are recognized by the immune system and induce an immune reaction. Vaccination recognition):
  • Cell-mediated immunity Cell-mediated immunity Manifestations of the immune response which are mediated by antigen-sensitized T-lymphocytes via lymphokines or direct cytotoxicity. This takes place in the absence of circulating antibody or where antibody plays a subordinate role. Squamous Cell Carcinoma (SCC): adaptive response in the cells/tissues involving the T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions
  • Humoral immunity: adaptive response in fluids (“humoral”) involving B cells B cells Lymphoid cells concerned with humoral immunity. They are short-lived cells resembling bursa-derived lymphocytes of birds in their production of immunoglobulin upon appropriate stimulation. B cells: Types and Functions and immunoglobulins Immunoglobulins Immunoglobulins (Igs), also known as antibodies, are glycoprotein molecules produced by plasma cells that act in immune responses by recognizing and binding particular antigens. The various Ig classes are IgG (the most abundant), IgM, IgE, IgD, and IgA, which differ in their biologic features, structure, target specificity, and distribution. Immunoglobulins: Types and Functions

Innate vs adaptive immunity

Components of the Adaptive Immune System

Responding to microbial invaders is the responsibility of the immune system Immune system The body’s defense mechanism against foreign organisms or substances and deviant native cells. It includes the humoral immune response and the cell-mediated response and consists of a complex of interrelated cellular, molecular, and genetic components. Primary Lymphatic Organs. Often the innate immune system Immune system The body’s defense mechanism against foreign organisms or substances and deviant native cells. It includes the humoral immune response and the cell-mediated response and consists of a complex of interrelated cellular, molecular, and genetic components. Primary Lymphatic Organs has the capability to contain the pathogens, but invaders may evolve to evade innate immunity Innate immunity The capacity of a normal organism to remain unaffected by microorganisms and their toxins. It results from the presence of naturally occurring anti-infective agents, constitutional factors such as body temperature and immediate acting immune cells such as natural killer cells. Innate Immunity: Phagocytes and Antigen Presentation. The next line of defense is the adaptive immune system Immune system The body’s defense mechanism against foreign organisms or substances and deviant native cells. It includes the humoral immune response and the cell-mediated response and consists of a complex of interrelated cellular, molecular, and genetic components. Primary Lymphatic Organs.

Adaptive immune system Immune system The body’s defense mechanism against foreign organisms or substances and deviant native cells. It includes the humoral immune response and the cell-mediated response and consists of a complex of interrelated cellular, molecular, and genetic components. Primary Lymphatic Organs definition

• Cell-mediated immunity Cell-mediated immunity Manifestations of the immune response which are mediated by antigen-sensitized T-lymphocytes via lymphokines or direct cytotoxicity. This takes place in the absence of circulating antibody or where antibody plays a subordinate role. Squamous Cell Carcinoma (SCC) and humoral adaptive immunity Humoral Adaptive Immunity Humoral adaptive immunity is an integral part of the adaptive immune system, which mounts a highly specific defense against pathogens but takes a longer time to respond (compared to the innate immune system). Humoral immunity is the arm of the immune system protecting the extracellular fluids of the lymphatics (lymph), interstitium, and circulatory system (plasma) from microbial contamination mediated through soluble molecules. Humoral Adaptive Immunity
• Composed of lymphocytes Lymphocytes Lymphocytes are heterogeneous WBCs involved in immune response. Lymphocytes develop from the bone marrow, starting from hematopoietic stem cells (HSCs) and progressing to common lymphoid progenitors (CLPs). B and T lymphocytes and natural killer (NK) cells arise from the lineage. Lymphocytes: Histology (T helper cells, cytotoxic Cytotoxic Parvovirus B19 T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions) and secreted proteins Proteins Linear polypeptides that are synthesized on ribosomes and may be further modified, crosslinked, cleaved, or assembled into complex proteins with several subunits. The specific sequence of amino acids determines the shape the polypeptide will take, during protein folding, and the function of the protein. Energy Homeostasis ( antibodies Antibodies Immunoglobulins (Igs), also known as antibodies, are glycoprotein molecules produced by plasma cells that act in immune responses by recognizing and binding particular antigens. The various Ig classes are IgG (the most abundant), IgM, IgE, IgD, and IgA, which differ in their biologic features, structure, target specificity, and distribution. Immunoglobulins: Types and Functions produced by B cells B cells Lymphoid cells concerned with humoral immunity. They are short-lived cells resembling bursa-derived lymphocytes of birds in their production of immunoglobulin upon appropriate stimulation. B cells: Types and Functions)
• Functionality takes days; however, once engaged, repeat encounters with the offending agent elicit a faster response.
• The B and T cell components:
  • Diversity: respond to millions of antigens
  • Specificity: immune response tailored to the specific antigen Antigen Substances that are recognized by the immune system and induce an immune reaction. Vaccination
  • Memory Memory Complex mental function having four distinct phases: (1) memorizing or learning, (2) retention, (3) recall, and (4) recognition. Clinically, it is usually subdivided into immediate, recent, and remote memory. Psychiatric Assessment: can respond many years later

Cell-mediated immunity Cell-mediated immunity Manifestations of the immune response which are mediated by antigen-sensitized T-lymphocytes via lymphokines or direct cytotoxicity. This takes place in the absence of circulating antibody or where antibody plays a subordinate role. Squamous Cell Carcinoma (SCC)

• Primary effectors: T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions
  • CD4+ T (helper) cells: Different subsets perform multiple functions, including cytokine production and activation of macrophages Macrophages The relatively long-lived phagocytic cell of mammalian tissues that are derived from blood monocytes. Main types are peritoneal macrophages; alveolar macrophages; histiocytes; kupffer cells of the liver; and osteoclasts. They may further differentiate within chronic inflammatory lesions to epithelioid cells or may fuse to form foreign body giant cells or langhans giant cells. Innate Immunity: Phagocytes and Antigen Presentation.
  • CD8+ T ( cytotoxic Cytotoxic Parvovirus B19) cells: defend against intracellular bacteria Bacteria Bacteria are prokaryotic single-celled microorganisms that are metabolically active and divide by binary fission. Some of these organisms play a significant role in the pathogenesis of diseases. Bacteriology and viruses Viruses Minute infectious agents whose genomes are composed of DNA or RNA, but not both. They are characterized by a lack of independent metabolism and the inability to replicate outside living host cells. Virology via destruction of infected cells
  • Memory Memory Complex mental function having four distinct phases: (1) memorizing or learning, (2) retention, (3) recall, and (4) recognition. Clinically, it is usually subdivided into immediate, recent, and remote memory. Psychiatric Assessment T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions: respond to antigen Antigen Substances that are recognized by the immune system and induce an immune reaction. Vaccination reexposure
• Other components:
  • T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions are dependent on cytokines Cytokines Non-antibody proteins secreted by inflammatory leukocytes and some non-leukocytic cells, that act as intercellular mediators. They differ from classical hormones in that they are produced by a number of tissue or cell types rather than by specialized glands. They generally act locally in a paracrine or autocrine rather than endocrine manner. Adaptive Immune Response (soluble proteins Proteins Linear polypeptides that are synthesized on ribosomes and may be further modified, crosslinked, cleaved, or assembled into complex proteins with several subunits. The specific sequence of amino acids determines the shape the polypeptide will take, during protein folding, and the function of the protein. Energy Homeostasis released by different cells, which play overlapping roles in both innate and adaptive immunity).
  • Dendritic cells Dendritic cells Specialized cells of the hematopoietic system that have branch-like extensions. They are found throughout the lymphatic system, and in non-lymphoid tissues such as skin and the epithelia of the intestinal, respiratory, and reproductive tracts. They trap and process antigens, and present them to T-cells, thereby stimulating cell-mediated immunity. They are different from the non-hematopoietic follicular dendritic cells, which have a similar morphology and immune system function, but with respect to humoral immunity (antibody production). Skin: Structure and Functions and macrophages Macrophages The relatively long-lived phagocytic cell of mammalian tissues that are derived from blood monocytes. Main types are peritoneal macrophages; alveolar macrophages; histiocytes; kupffer cells of the liver; and osteoclasts. They may further differentiate within chronic inflammatory lesions to epithelioid cells or may fuse to form foreign body giant cells or langhans giant cells. Innate Immunity: Phagocytes and Antigen Presentation in the innate immune system Immune system The body’s defense mechanism against foreign organisms or substances and deviant native cells. It includes the humoral immune response and the cell-mediated response and consists of a complex of interrelated cellular, molecular, and genetic components. Primary Lymphatic Organs present antigens to T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions.

Humoral adaptive immunity Humoral Adaptive Immunity Humoral adaptive immunity is an integral part of the adaptive immune system, which mounts a highly specific defense against pathogens but takes a longer time to respond (compared to the innate immune system). Humoral immunity is the arm of the immune system protecting the extracellular fluids of the lymphatics (lymph), interstitium, and circulatory system (plasma) from microbial contamination mediated through soluble molecules. Humoral Adaptive Immunity

• Antibody-mediated immunity
• B cells B cells Lymphoid cells concerned with humoral immunity. They are short-lived cells resembling bursa-derived lymphocytes of birds in their production of immunoglobulin upon appropriate stimulation. B cells: Types and Functions:
  • Differentiate into plasma cells Plasma cells Specialized forms of antibody-producing B-lymphocytes. They synthesize and secrete immunoglobulin. They are found only in lymphoid organs and at sites of immune responses and normally do not circulate in the blood or lymph. Humoral Adaptive Immunity, producing antibodies Antibodies Immunoglobulins (Igs), also known as antibodies, are glycoprotein molecules produced by plasma cells that act in immune responses by recognizing and binding particular antigens. The various Ig classes are IgG (the most abundant), IgM, IgE, IgD, and IgA, which differ in their biologic features, structure, target specificity, and distribution. Immunoglobulins: Types and Functions with the help of T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions
  • Differentiate into memory cells Memory cells Cells that outlived a previous infection Adaptive Immune Response, briskly responding to reinfection
  • Act as antigen-presenting cells Antigen-presenting cells A heterogeneous group of immunocompetent cells that mediate the cellular immune response by processing and presenting antigens to the T-cells. Traditional antigen-presenting cells include macrophages; dendritic cells; langerhans cells; and B-lymphocytes. Follicular dendritic cells are not traditional antigen-presenting cells, but because they hold antigen on their cell surface in the form of immune complexes for b-cell recognition they are considered so by some authors. Adaptive Immune Response to T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions (expressing class II MHC)
• Antibodies Antibodies Immunoglobulins (Igs), also known as antibodies, are glycoprotein molecules produced by plasma cells that act in immune responses by recognizing and binding particular antigens. The various Ig classes are IgG (the most abundant), IgM, IgE, IgD, and IgA, which differ in their biologic features, structure, target specificity, and distribution. Immunoglobulins: Types and Functions, along with complement, help the cells of the innate system against extracellular, encapsulated Encapsulated Klebsiella bacteria Bacteria Bacteria are prokaryotic single-celled microorganisms that are metabolically active and divide by binary fission. Some of these organisms play a significant role in the pathogenesis of diseases. Bacteriology.
• Antibodies Antibodies Immunoglobulins (Igs), also known as antibodies, are glycoprotein molecules produced by plasma cells that act in immune responses by recognizing and binding particular antigens. The various Ig classes are IgG (the most abundant), IgM, IgE, IgD, and IgA, which differ in their biologic features, structure, target specificity, and distribution. Immunoglobulins: Types and Functions can neutralize toxins and viruses Viruses Minute infectious agents whose genomes are composed of DNA or RNA, but not both. They are characterized by a lack of independent metabolism and the inability to replicate outside living host cells. Virology.

Development of T Cells

T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions

• Derived from common lymphoid progenitors Common lymphoid progenitors Stem cells from which B-lymphocytes; T-lymphocytes; natural killer cells; and some dendritic cells derive. Bone Marrow: Composition and Hematopoiesis
• Unlike B cells B cells Lymphoid cells concerned with humoral immunity. They are short-lived cells resembling bursa-derived lymphocytes of birds in their production of immunoglobulin upon appropriate stimulation. B cells: Types and Functions, T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions from bone marrow Bone marrow The soft tissue filling the cavities of bones. Bone marrow exists in two types, yellow and red. Yellow marrow is found in the large cavities of large bones and consists mostly of fat cells and a few primitive blood cells. Red marrow is a hematopoietic tissue and is the site of production of erythrocytes and granular leukocytes. Bone marrow is made up of a framework of connective tissue containing branching fibers with the frame being filled with marrow cells. Bone Marrow: Composition and Hematopoiesis migrate to the thymus Thymus A single, unpaired primary lymphoid organ situated in the mediastinum, extending superiorly into the neck to the lower edge of the thyroid gland and inferiorly to the fourth costal cartilage. It is necessary for normal development of immunologic function early in life. By puberty, it begins to involute and much of the tissue is replaced by fat. Lymphatic Drainage System: Anatomy to complete development.
• Before entering the thymus Thymus A single, unpaired primary lymphoid organ situated in the mediastinum, extending superiorly into the neck to the lower edge of the thyroid gland and inferiorly to the fourth costal cartilage. It is necessary for normal development of immunologic function early in life. By puberty, it begins to involute and much of the tissue is replaced by fat. Lymphatic Drainage System: Anatomy, T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions lack the T cell receptor Receptor Receptors are proteins located either on the surface of or within a cell that can bind to signaling molecules known as ligands (e.g., hormones) and cause some type of response within the cell. Receptors (TCR) (the protein complex binding to a specific antigen Antigen Substances that are recognized by the immune system and induce an immune reaction. Vaccination)
• Development stages:
  • TCR assembly
  • Interaction with self antigens
  • Positive and negative selection Selection Lymphocyte activation by a specific antigen thus triggering clonal expansion of lymphocytes already capable of mounting an immune response to the antigen. B cells: Types and Functions: leads to MHC restriction and elimination Elimination The initial damage and destruction of tumor cells by innate and adaptive immunity. Completion of the phase means no cancer growth. Cancer Immunotherapy of autoreactive cells
  • Expression of CD4 (become helper T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions) or CD8 (become cytotoxic Cytotoxic Parvovirus B19 T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions)
• Released naive mature T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions from the thymus Thymus A single, unpaired primary lymphoid organ situated in the mediastinum, extending superiorly into the neck to the lower edge of the thyroid gland and inferiorly to the fourth costal cartilage. It is necessary for normal development of immunologic function early in life. By puberty, it begins to involute and much of the tissue is replaced by fat. Lymphatic Drainage System: Anatomy express surface TCR with coreceptors CD4 or CD8. 

TCR

• A heterodimer consisting of 2 transmembrane polypeptide chains: α and β chains (the majority of T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions) or γ and δ chains (the minority of T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions)
• Assembly of the 2 chains requires gene rearrangements Gene rearrangements The ordered rearrangement of gene regions by DNA recombination such as that which occurs normally during development. Humoral Adaptive Immunity, which contribute to TCR diversity.
• Structurally, each TCR α and β chain has:
  • Variable Variable Variables represent information about something that can change. The design of the measurement scales, or of the methods for obtaining information, will determine the data gathered and the characteristics of that data. As a result, a variable can be qualitative or quantitative, and may be further classified into subgroups. Types of Variables regions and a constant region Constant region The domains of the immunoglobulin molecules that are invariable in their amino acid sequence within any class or subclass of immunoglobulin. They confer biological as well as structural functions to immunoglobulins. One each on both the light chains and the heavy chains comprises the c-terminus half of the immunoglobulin fab fragment and two or three of them make up the rest of the heavy chains (all of the immunoglobulin Fc fragment). Immunoglobulins: Types and Functions
  • Hydrophobic transmembrane region 
  • Short cytoplasmic region 
• Spans the cytoplasmic membrane with variable Variable Variables represent information about something that can change. The design of the measurement scales, or of the methods for obtaining information, will determine the data gathered and the characteristics of that data. As a result, a variable can be qualitative or quantitative, and may be further classified into subgroups. Types of Variables binding regions projecting into the extracellular space to bind BIND Hyperbilirubinemia of the Newborn antigens (similar to the antigen-binding fragment ( Fab Fab Univalent antigen-binding fragments composed of one entire immunoglobulin light chain and the amino terminal end of one of the immunoglobulin heavy chains from the hinge region, linked to each other by disulfide bonds. Fab contains the immunoglobulin variable regions, which are part of the antigen-binding site, and the first immunoglobulin constant regions. This fragment can be obtained by digestion of immunoglobulins with the proteolytic enzyme papain. Immunoglobulins: Types and Functions) of an antibody):
  • The processed antigens are associated with class I or class II MHC molecules.
  • CD4 molecules bind BIND Hyperbilirubinemia of the Newborn to class II MHC molecules; CD8 molecules bind BIND Hyperbilirubinemia of the Newborn to class I MHC molecules.

T cell activation

• For proliferation and activation to occur, naive mature T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions must interact with a foreign antigen Antigen Substances that are recognized by the immune system and induce an immune reaction. Vaccination.
• T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions circulate in the blood and go to the secondary lymphoid tissues.
• The secondary lymphoid organs Lymphoid organs A system of organs and tissues that process and transport immune cells and lymph. Primary Lymphatic Organs (e.g., lymph Lymph The interstitial fluid that is in the lymphatic system. Secondary Lymphatic Organs nodes) filter antigenic material allowing the naive mature T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions:
  • To interact with antigen-presenting cells Antigen-presenting cells A heterogeneous group of immunocompetent cells that mediate the cellular immune response by processing and presenting antigens to the T-cells. Traditional antigen-presenting cells include macrophages; dendritic cells; langerhans cells; and B-lymphocytes. Follicular dendritic cells are not traditional antigen-presenting cells, but because they hold antigen on their cell surface in the form of immune complexes for b-cell recognition they are considered so by some authors. Adaptive Immune Response such as macrophages Macrophages The relatively long-lived phagocytic cell of mammalian tissues that are derived from blood monocytes. Main types are peritoneal macrophages; alveolar macrophages; histiocytes; kupffer cells of the liver; and osteoclasts. They may further differentiate within chronic inflammatory lesions to epithelioid cells or may fuse to form foreign body giant cells or langhans giant cells. Innate Immunity: Phagocytes and Antigen Presentation or dendritic cells Dendritic cells Specialized cells of the hematopoietic system that have branch-like extensions. They are found throughout the lymphatic system, and in non-lymphoid tissues such as skin and the epithelia of the intestinal, respiratory, and reproductive tracts. They trap and process antigens, and present them to T-cells, thereby stimulating cell-mediated immunity. They are different from the non-hematopoietic follicular dendritic cells, which have a similar morphology and immune system function, but with respect to humoral immunity (antibody production). Skin: Structure and Functions
  • To sample the antigens to become activated
• The full activation of a T cell ready to mount an immune response requires 2 signals (see image):
  • Signal 1: TCR recognizes the cognate antigen Antigen Substances that are recognized by the immune system and induce an immune reaction. Vaccination presented by the antigen-presenting cell (e.g., dendritic cell).
  • Signal 2: costimulation: 
    • Provided by a costimulatory molecule Costimulatory molecule T cells: Types and Functions
    • Best characterized by a B7 protein in the antigen-presenting cell interacting with CD28 CD28 Costimulatory t-lymphocyte receptors that have specificity for CD80 antigen and CD86 antigen. Activation of this receptor results in increased t-cell proliferation, cytokine production and promotion of t-cell survival. T cells: Types and Functions of the T cell 
• Activated T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions proliferate and may become: 
  • Effector T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions:
    • Migrate from the lymphoid organs Lymphoid organs A system of organs and tissues that process and transport immune cells and lymph. Primary Lymphatic Organs into the circulation Circulation The movement of the blood as it is pumped through the cardiovascular system. ABCDE Assessment and tissues to reach sites of infection
    • Able to further differentiate to memory cells Memory cells Cells that outlived a previous infection Adaptive Immune Response
  • Memory Memory Complex mental function having four distinct phases: (1) memorizing or learning, (2) retention, (3) recall, and (4) recognition. Clinically, it is usually subdivided into immediate, recent, and remote memory. Psychiatric Assessment T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions

T Cells in the Immune System

Activated T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions

• Activated T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions become effector CD4+ or CD8+ T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions and memory Memory Complex mental function having four distinct phases: (1) memorizing or learning, (2) retention, (3) recall, and (4) recognition. Clinically, it is usually subdivided into immediate, recent, and remote memory. Psychiatric Assessment T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions:
  • CD4+ T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions: functional categories of activated CD4+ T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions are influenced by secreted cytokines Cytokines Non-antibody proteins secreted by inflammatory leukocytes and some non-leukocytic cells, that act as intercellular mediators. They differ from classical hormones in that they are produced by a number of tissue or cell types rather than by specialized glands. They generally act locally in a paracrine or autocrine rather than endocrine manner. Adaptive Immune Response.
    • T helper (Th) cells: Th1 Th1 A subset of helper-inducer T-lymphocytes which synthesize and secrete interleukin-2; interferon-gamma; and interleukin-12. Due to their ability to kill antigen-presenting cells and their lymphokine-mediated effector activity, th1 cells are associated with vigorous delayed-type hypersensitivity reactions. T cells: Types and Functions and Th2 Th2 A subset of helper-inducer T-lymphocytes which synthesize and secrete the interleukins il-4; il-5; il-6; and il-10. These cytokines influence b-cell development and antibody production as well as augmenting humoral responses. T cells: Types and Functions (most studied), Th9, Th17 Th17 A subset of helper-effector T-lymphocytes which synthesize and secrete interleukins il-17; il-17f; and il-22. These cytokines are involved in host defenses and tissue inflammation in autoimmune diseases. T cells: Types and Functions, Th22, and T follicular helper (Tfh) 
    • Subset of regulatory T cell (Treg)
  • CD8+ T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions: cytotoxic Cytotoxic Parvovirus B19 T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions (Tc)
  • Memory Memory Complex mental function having four distinct phases: (1) memorizing or learning, (2) retention, (3) recall, and (4) recognition. Clinically, it is usually subdivided into immediate, recent, and remote memory. Psychiatric Assessment T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions
• Cell surface markers:
  • T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions: TCR, CD3 CD3 Complex of at least five membrane-bound polypeptides in mature T-lymphocytes that are non-covalently associated with one another and with the T-cell receptor. The CD3 complex includes the gamma, delta, epsilon, zeta, and eta chains (subunits). When antigen binds to the T-cell receptor, the CD3 complex transduces the activating signals to the cytoplasm of the T-cell. The CD3 gamma and delta chains (subunits) are separate from and not related to the gamma/delta chains of the T-cell receptor. T cells: Types and Functions
  • Th cells: CD4, CD40L, CXCR4 CXCR4 Cxcr receptors with specificity for cxcl12 chemokine. The receptors may play a role in hematopoiesis regulation and can also function as coreceptors for the human immunodeficiency virus. HIV Infection and AIDS and CCR5 CCR5 Ccr receptors with specificity for chemokine ccl3; chemokine ccl4; and chemokine ccl5. They are expressed at high levels in T-lymphocytes; B-lymphocytes; macrophages; mast cells; and nk cells. The ccr5 receptor is used by the human immunodeficiency virus to infect cells. HIV Infection and AIDS (coreceptors for HIV-1 HIV-1 The type species of lentivirus and the etiologic agent of aids. It is characterized by its cytopathic effect and affinity for the T4-lymphocyte. HIV Infection and AIDS entry into CD4+ cells)
  • Tregs: CD4, CD25
  • Tc: CD8
• Aside from surface markers, T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions and subsets are identified by cytokine profiles.

Description of CD4+ T cell subsets

Other CD4+ T cell subsets

• Th9 and Th22 were recently discovered.
• Th9: 
  • Stimulated by IL-4, TGF-β
  • Important in antitumor immunity, allergies Allergies A medical specialty concerned with the hypersensitivity of the individual to foreign substances and protection from the resultant infection or disorder. Selective IgA Deficiency, and autoimmune diseases Autoimmune diseases Disorders that are characterized by the production of antibodies that react with host tissues or immune effector cells that are autoreactive to endogenous peptides. Selective IgA Deficiency
• Th22:
  • Produces IL-22 (like Th17 Th17 A subset of helper-effector T-lymphocytes which synthesize and secrete interleukins il-17; il-17f; and il-22. These cytokines are involved in host defenses and tissue inflammation in autoimmune diseases. T cells: Types and Functions cells)
  • Involved in mucosal immunity

CD8+ T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions

• Cytotoxic Cytotoxic Parvovirus B19 or cytolytic T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions
• Requires cytokine ( interleukin-2 Interleukin-2 A soluble substance elaborated by antigen- or mitogen-stimulated T-lymphocytes which induces DNA synthesis in naive lymphocytes. Interleukins (IL-2)) stimulation (from Th1 Th1 A subset of helper-inducer T-lymphocytes which synthesize and secrete interleukin-2; interferon-gamma; and interleukin-12. Due to their ability to kill antigen-presenting cells and their lymphokine-mediated effector activity, th1 cells are associated with vigorous delayed-type hypersensitivity reactions. T cells: Types and Functions cells) to be activated, then leaves the secondary lymphoid organ and circulates in search of targets
• Produces cytokines Cytokines Non-antibody proteins secreted by inflammatory leukocytes and some non-leukocytic cells, that act as intercellular mediators. They differ from classical hormones in that they are produced by a number of tissue or cell types rather than by specialized glands. They generally act locally in a paracrine or autocrine rather than endocrine manner. Adaptive Immune Response interferon ( IFN IFN Interferon (IFN) is a cytokine with antiviral properties (it interferes with viral infections) and various roles in immunoregulation. The different types are type I IFN (IFN-ɑ and IFN-β), type II IFN (IFN-ɣ), and type III IFN (IFN-ƛ). Interferons)-γ, tumor necrosis factor Tumor necrosis factor Tumor necrosis factor (TNF) is a major cytokine, released primarily by macrophages in response to stimuli. The presence of microbial products and dead cells and injury are among the stimulating factors. This protein belongs to the TNF superfamily, a group of ligands and receptors performing functions in inflammatory response, morphogenesis, and cell proliferation. Tumor Necrosis Factor (TNF) ( TNF TNF Tumor necrosis factor (TNF) is a major cytokine, released primarily by macrophages in response to stimuli. The presence of microbial products and dead cells and injury are among the stimulating factors. This protein belongs to the TNF superfamily, a group of ligands and receptors performing functions in inflammatory response, morphogenesis, and cell proliferation. Tumor Necrosis Factor (TNF))-α, and TNF-β
• Transcription factor Transcription factor Generic term for proteins necessary for transcription Regulation of Transcription: RUNX3
• Functions include killing of:
  • Pathogens
  • Infected cells
  • Tumor Tumor Inflammation cells
  • Allografts Allografts Tissues, cells, or organs transplanted between genetically different individuals of the same species. Organ Transplantation
• Cytotoxicity occurs via:
  • Granule exocytosis Exocytosis Cellular release of material within membrane-limited vesicles by fusion of the vesicles with the cell membrane. The Cell: Cell Membrane: Granule contents (including granzymes Granzymes A family of serine endopeptidases found in the secretory granules of leukocytes such as cytotoxic T-lymphocytes and natural killer cells. When secreted into the intercellular space granzymes act to eliminate transformed and virus-infected host cells. Lymphocytes: Histology and perforins) enter the target cell and activate the caspase pathway, which leads to apoptosis Apoptosis A regulated cell death mechanism characterized by distinctive morphologic changes in the nucleus and cytoplasm, including the endonucleolytic cleavage of genomic DNA, at regularly spaced, internucleosomal sites, I.e., DNA fragmentation. It is genetically-programmed and serves as a balance to mitosis in regulating the size of animal tissues and in mediating pathologic processes associated with tumor growth. Ischemic Cell Damage.
  • Expression of Fas Ligand Fas ligand A transmembrane protein belonging to the tumor necrosis factor superfamily that was originally discovered on cells of the lymphoid-myeloid lineage, including activated T-lymphocytes and natural killer cells. It plays an important role in immune homeostasis and cell-mediated toxicity by binding to the fas receptor and triggering apoptosis. Tumor Necrosis Factor (TNF) (FasL): Fas ( receptor Receptor Receptors are proteins located either on the surface of or within a cell that can bind to signaling molecules known as ligands (e.g., hormones) and cause some type of response within the cell. Receptors in the cell)-FasL (ligand in CD8+ T cell) interaction activates the caspase pathway, leading to cell death Cell death Injurious stimuli trigger the process of cellular adaptation, whereby cells respond to withstand the harmful changes in their environment. Overwhelmed adaptive mechanisms lead to cell injury. Mild stimuli produce reversible injury. If the stimulus is severe or persistent, injury becomes irreversible. Apoptosis is programmed cell death, a mechanism with both physiologic and pathologic effects. Cell Injury and Death.
• Clinical relevance:
  • Prominent role in intracellular pathogens Intracellular pathogens IL-12 Receptor Deficiency (e.g., Listeria monocytogenes Listeria monocytogenes Listeria spp. are motile, flagellated, gram-positive, facultative intracellular bacilli. The major pathogenic species is Listeria monocytogenes. Listeria are part of the normal gastrointestinal flora of domestic mammals and poultry and are transmitted to humans through the ingestion of contaminated food, especially unpasteurized dairy products. Listeria Monocytogenes/Listeriosis) as the pathogens spend little time in circulation Circulation The movement of the blood as it is pumped through the cardiovascular system. ABCDE Assessment (less susceptibility to antibodies Antibodies Immunoglobulins (Igs), also known as antibodies, are glycoprotein molecules produced by plasma cells that act in immune responses by recognizing and binding particular antigens. The various Ig classes are IgG (the most abundant), IgM, IgE, IgD, and IgA, which differ in their biologic features, structure, target specificity, and distribution. Immunoglobulins: Types and Functions)
  • Similar importance in the immune defense against viruses Viruses Minute infectious agents whose genomes are composed of DNA or RNA, but not both. They are characterized by a lack of independent metabolism and the inability to replicate outside living host cells. Virology (e.g., HIV HIV Anti-HIV Drugs)

Memory Memory Complex mental function having four distinct phases: (1) memorizing or learning, (2) retention, (3) recall, and (4) recognition. Clinically, it is usually subdivided into immediate, recent, and remote memory. Psychiatric Assessment T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions

• Can be either CD4+ or CD8+
• Mounts immune response years after initial exposure
• Following initial exposure to antigens, some T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions develop into memory cells Memory cells Cells that outlived a previous infection Adaptive Immune Response:
  • Cells initially reside in lymphoid tissues (central memory Memory Complex mental function having four distinct phases: (1) memorizing or learning, (2) retention, (3) recall, and (4) recognition. Clinically, it is usually subdivided into immediate, recent, and remote memory. Psychiatric Assessment T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions)
  • T memory cells Memory cells Cells that outlived a previous infection Adaptive Immune Response then reside in peripheral tissues (effector memory cells Memory cells Cells that outlived a previous infection Adaptive Immune Response)
  • Become effector T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions following reinfection by the same antigen Antigen Substances that are recognized by the immune system and induce an immune reaction. Vaccination

T regulatory cells Regulatory cells Cd4-positive T cells that inhibit immunopathology or autoimmune disease in vivo. They inhibit the immune response by influencing the activity of other cell types. Regulatory T-cells include naturally occurring CD4+CD25+ cells, il-10 secreting tr1 cells, and TH3 cells. T cells: Types and Functions

• Because unrestrained T cell response can become pathologic, Tregs are present to prevent excessive inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body’s defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation and tissue damage.
• Can down regulate the activity of many immune cells including:
  • CD4+ T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions
  • CD8+ T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions
  • Dendritic cells Dendritic cells Specialized cells of the hematopoietic system that have branch-like extensions. They are found throughout the lymphatic system, and in non-lymphoid tissues such as skin and the epithelia of the intestinal, respiratory, and reproductive tracts. They trap and process antigens, and present them to T-cells, thereby stimulating cell-mediated immunity. They are different from the non-hematopoietic follicular dendritic cells, which have a similar morphology and immune system function, but with respect to humoral immunity (antibody production). Skin: Structure and Functions (via cell surfaces of cytotoxic Cytotoxic Parvovirus B19 T-lymphocyte antigen Antigen Substances that are recognized by the immune system and induce an immune reaction. Vaccination 4 (CTLA-4) and lymphocyte activation gene Gene A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. Basic Terms of Genetics (LAG-3))
  • B cells B cells Lymphoid cells concerned with humoral immunity. They are short-lived cells resembling bursa-derived lymphocytes of birds in their production of immunoglobulin upon appropriate stimulation. B cells: Types and Functions
  • Natural killer cells Natural killer cells A specialized subset of T-lymphocytes that exhibit features of innate immunity similar to that of natural killer cells. They are reactive to glycolipids presented in the context of the major histocompatibility complex (MHC) class I-like molecule, CD1D antigen. Lymphocytes: Histology
  • Eosinophils Eosinophils Granular leukocytes with a nucleus that usually has two lobes connected by a slender thread of chromatin, and cytoplasm containing coarse, round granules that are uniform in size and stainable by eosin. Innate Immunity: Phagocytes and Antigen Presentation, basophils Basophils Granular leukocytes characterized by a relatively pale-staining, lobate nucleus and cytoplasm containing coarse dark-staining granules of variable size and stainable by basic dyes. Innate Immunity: Phagocytes and Antigen Presentation, and mast cells Mast cells Granulated cells that are found in almost all tissues, most abundantly in the skin and the gastrointestinal tract. Like the basophils, mast cells contain large amounts of histamine and heparin. Unlike basophils, mast cells normally remain in the tissues and do not circulate in the blood. Mast cells, derived from the bone marrow stem cells, are regulated by the stem cell factor. Innate Immunity: Phagocytes and Antigen Presentation

Intraepithelial lymphocytes Lymphocytes Lymphocytes are heterogeneous WBCs involved in immune response. Lymphocytes develop from the bone marrow, starting from hematopoietic stem cells (HSCs) and progressing to common lymphoid progenitors (CLPs). B and T lymphocytes and natural killer (NK) cells arise from the lineage. Lymphocytes: Histology (IEL)

• Associated with the protection of the mucosal surface (intestinal tract, respiratory tract, genitourinary tract epithelium Epithelium The epithelium is a complex of specialized cellular organizations arranged into sheets and lining cavities and covering the surfaces of the body. The cells exhibit polarity, having an apical and a basal pole. Structures important for the epithelial integrity and function involve the basement membrane, the semipermeable sheet on which the cells rest, and interdigitations, as well as cellular junctions. Surface Epithelium: Histology, and skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions) 
• When pathogens invade the epithelial surface, IELs are the 1st immune cells to encounter the pathogens. 
• Predominantly activated T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions: CD8+ > CD 4+ cells at most sites (not all)
• TCR-αβ+ and TCR-γδ+ cells are found within IEL groups.

Cytokines in Cell-mediated Immunity

Cytokines Cytokines Non-antibody proteins secreted by inflammatory leukocytes and some non-leukocytic cells, that act as intercellular mediators. They differ from classical hormones in that they are produced by a number of tissue or cell types rather than by specialized glands. They generally act locally in a paracrine or autocrine rather than endocrine manner. Adaptive Immune Response

• Soluble proteins released by different cells in response to various inflammatory stimuli:
  • Play overlapping roles in both innate and adaptive immunity
  • Important in cell-mediated adaptive immunity: T-cell differentiation depends on cytokines, and T cells produce cytokines
• According to function or cell of origin:
  • Lymphokines: cytokines made by lymphocytes 
  • Monokines: cytokines made by monocytes 
  • Chemokines: cytokines with chemotactic actions
• Includes:
  • IL: cytokines made by a leukocyte and acting on other leukocytes
  • IFN: originally named for the function of “interfering” with viral infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease:
    • Type I interferons Interferons Interferon (IFN) is a cytokine with antiviral properties (it interferes with viral infections) and various roles in immunoregulation. The different types are type I IFN (IFN-ɑ and IFN-β), type II IFN (IFN-ɣ), and type III IFN (IFN-ƛ). Interferons (IFN-α and IFN-β): mainly function to prevent viral replication inside cells
    • Type II interferon Type II interferon The major interferon produced by mitogenically or antigenically stimulated lymphocytes. It is structurally different from type I interferon and its major activity is immunoregulation. It has been implicated in the expression of class II histocompatibility antigens in cells that do not normally produce them, leading to autoimmune diseases. Interferons (IFN-γ): activates macrophages Macrophages The relatively long-lived phagocytic cell of mammalian tissues that are derived from blood monocytes. Main types are peritoneal macrophages; alveolar macrophages; histiocytes; kupffer cells of the liver; and osteoclasts. They may further differentiate within chronic inflammatory lesions to epithelioid cells or may fuse to form foreign body giant cells or langhans giant cells. Innate Immunity: Phagocytes and Antigen Presentation
    • Type III (IFN-ƛ): antiviral Antiviral Antivirals for Hepatitis B activity 
  • TNF TNF Tumor necrosis factor (TNF) is a major cytokine, released primarily by macrophages in response to stimuli. The presence of microbial products and dead cells and injury are among the stimulating factors. This protein belongs to the TNF superfamily, a group of ligands and receptors performing functions in inflammatory response, morphogenesis, and cell proliferation. Tumor Necrosis Factor (TNF)
  • Transforming growth factor (TGF)
  • Other growth or stimulating factors

Major cytokines Cytokines Non-antibody proteins secreted by inflammatory leukocytes and some non-leukocytic cells, that act as intercellular mediators. They differ from classical hormones in that they are produced by a number of tissue or cell types rather than by specialized glands. They generally act locally in a paracrine or autocrine rather than endocrine manner. Adaptive Immune Response produced by T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions

Cytokines and Clinical Applications

Cytokine inhibitors and applications

Therapeutic cytokines Cytokines Non-antibody proteins secreted by inflammatory leukocytes and some non-leukocytic cells, that act as intercellular mediators. They differ from classical hormones in that they are produced by a number of tissue or cell types rather than by specialized glands. They generally act locally in a paracrine or autocrine rather than endocrine manner. Adaptive Immune Response and applications

Clinical Relevance

• Chronic mucocutaneous candidiasis (CMCC): an autoimmune syndrome with features including chronic, noninvasive Candida infections of the skin, nails, and mucous membranes. The condition is associated with autoimmune manifestations (most commonly endocrinopathies). Hypoparathyroidism is the most common endocrine abnormality and occurs in 30% of individuals. Adrenal insufficiency occurs in > 60% of cases by 15 years of age. Chronic mucocutaneous candidiasis is due to genetic defects in the immune system, including those affecting autoimmune regulator (AIRE), which is important in the negative selection of T cells, and the IL-17 pathway (among others).
• Immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome: a disease caused by mutations in the gene from transcription factor FOXP3. The defining feature is Treg cell impairment, which manifests as an autoimmune disease with an allergic inflammation. The disease typically presents in male infants with a triad of enteropathy, dermatitis, and autoimmune endocrinopathy (usually type 1 diabetes or thyroiditis). Diarrhea can be profound and associated with dehydration, malabsorption, metabolic acidosis, renal insufficiency, and failure to thrive. Other manifestations include severe food allergies, chronic autoimmune hepatitis, autoimmune cytopenias, interstitial nephritis, and developmental delays. Diagnosis is by mutational analysis of the FOXP3 gene. The only curative therapy available is hematopoietic cell transplantation.
• Adult T cell leukemia/lymphoma: a rare, but often aggressive, mature T cell malignancy caused by chronic infection of CD4+ cells with the human T-lymphotropic virus (HTLV)-I. The infection is endemic in Japan, the Caribbean, and Central Africa. General presentation is widespread involvement of lymph nodes, peripheral blood, and/or the skin. The known clinical variants are acute, lymphomatous, chronic, and smoldering. Each variant has a different clinical course. The characteristic feature seen in peripheral blood is “clover leaf” or “flower cells” (cells with bizarre, hyperlobulated nuclei). Diagnosis is based on clinical presentation, morphologic and immunophenotypic changes of the malignant cells, and confirmed HTLV-I HTLV-I Acute Lymphoblastic Leukemia infection. Treatment is tailored to the subtype, but options include antiviral Antiviral Antivirals for Hepatitis B agents, monoclonal antibody therapy, chemotherapy Chemotherapy Osteosarcoma, and allogeneic stem cell transplantation Allogeneic Stem Cell Transplantation Acute Lymphoblastic Leukemia.