White Myeloid Cells

The myeloid lineage produces a diverse group of blood cells (leukocytes) involved in the defense of the body against foreign substances or infectious agents. Monocytes, neutrophils, eosinophils, basophils, and mast cells all arise from the common myeloid progenitor (CMP), which develops from bone marrow stem cells. However, leukocytes have different functions. Neutrophils kill invading bacteria and fungi, eosinophils increase in parasitic infections, basophils and mast cells are key to allergic response as sources of histamine, and monocytes are released from bone marrow to become macrophages in the tissues. The development in the bone marrow is regulated by different cytokines.

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White myeloid cells are leukocytes developed from the common myeloid progenitor (CMP), which is derived from hematopoietic stem cells (HSCs) of the bone marrow.

  • Not all leukocytes (WBCs) are derived from the myeloid progenitor.
  • 2 major groups of leukocytes:
    • Granulocytes (derived from the myeloid progenitor):
      • Basophils
      • Eosinophils
      • Neutrophils
      • Mast cells
    • Agranulocytes (derived from myeloid and lymphoid progenitors):
      • Monocytes (myeloid)
      • Lymphocytes (lymphoid)

Cell description

Table: Cell description of agranulocytes
TypeNucleusGranulesCharacteristics and functions
Monocyte (3%–7% of differential count)Kidney shaped (indented or C shaped)NoneCharacteristics:
  • Lifespan: hours to days
  • Largest leukocyte

  • Differentiate into populations of tissue macrophages (including dendritic cells and osteoclasts)
  • All cells derived from monocytes are antigen-presenting cells.
  • Search for microbial cells and mount an immune response
Table: Cell description of granulocytes
TypeNucleusGranulesCharacteristics and functions
Neutrophil (50%–70% of differential count)Multilobed (3–5 lobes)
  • Fine
  • Faintly pink
  • Approximately 6 hours (circulating)
  • Days (in tissues)

Target and function:
  • Kill and phagocytose bacteria
  • Destruct fungi, restrict the growth of larger fungi
Eosinophil (1%–3% of differential count)Bilobed
  • Large
  • Dark pink
  • Approximately 6 hours (circulating)
  • Days (in tissues)

Target and function:
  • Kill parasites and helminths
  • Immune response to allergic reactions
Basophil (0.5%–1% of differential count)Bilobed or trilobed
  • Large
  • Dark blue
  • Hours to days

Target and function:
  • Modulation of the inflammatory response by histamine secretion
  • Surface receptors for IgE
  • Supplements actions of mast cells
Mast cellRound (margins obscured by packed granules)Purple to red
  • Granules rich in histamine and heparin
  • Found in tissues, but not in blood
  • Modulation of the type 1 hypersensitivity reaction through IgE receptors


Myeloid cell production

  • Hematopoiesis:
    • 1st to 2nd month in utero: mesoderm of the yolk sac
    • By the 2nd month: moves to the liver (and spleen)
    • By the 5th month: occurs in the bone marrow, which becomes the predominant source of blood cells
  • Myelopoiesis starts with multipotent HSCs in the bone marrow.
  •  HSCs → multipotent progenitor (MPP) cells → CMP (which eventually differentiates into granulocytes, monocytes, platelets, and erythrocytes)
Bone marrow hematopoiesis

Bone marrow hematopoiesis: proliferation and differentiation of the formed elements of blood.
IL-3: interleukin-3
CFU-GEMM: colony-forming unit–granulocyte, erythrocyte, monocyte, megakaryocyte
IL-2: interleukin-2
IL-6: interleukin-6
CFU-GM: colony-forming unit–granulocyte-macrophage
GM-CSF: granulocyte-macrophage colony-stimulating factor
M-CSF: macrophage colony-stimulating factor
G-CSF: granulocyte colony-stimulating factor
IL-5: interleukin-5
NK: natural killer
TPO: thrombopoietin
EPO: erythropoietin

Image by Lecturio. License: CC BY-NC-SA 4.0


Table: Comparison of cytokines/growth factors
Cytokines/growth factorsActivitiesSource
Stem cell factor (SCF)Stimulates all hematopoietic progenitor cellsBone marrow stromal cells
Granulocyte-macrophage colony-stimulating factor (GM-CSF)Stimulates myeloid progenitor cellsEndothelial cells, T cells
Granulocyte colony-stimulating factor (G-CSF)Stimulates neutrophil precursor cellsEndothelial cells, macrophages
Monocyte colony-stimulating factor (M-CSF)Stimulates monocyte precursor cellsEndothelial cells, macrophages
Interleukin-1 (IL-1)Regulation of cytokine secretion of many leukocytesMacrophages, T helper cells
Interleukin-3 (IL-3)Mitogen for all granulocyte and megakaryocyte/erythrocyte progenitor cellsT helper cells
Interleukin-4 (IL-4)Development of basophils and mast cells, and activation of B-lymphocyteT helper cells
Interleukin-5 (IL-5)Development and activation of eosinophilsT helper cells


Neutrophils, eosinophils, basophils

  • Neutrophils are derived from the colony-forming unit granulocyte-macrophage (CFU-GM).
  • Eosinophils (Eo) and basophils (Ba) come from progenitor-cell CFU-Eo and CFU-Ba, respectively.
  • Subsequent stages:
    1. Myeloblast: 
      • 1st granulocytic precursor
      • Cytoplasm with no granules
      • Large nucleus and faint nucleoli
    2. Promyelocyte:
      • Azurophilic granules form.
      • The granules contain lysosomal hydrolases and myeloperoxidase.
    3. Myelocyte: 
      • 1st sign of differentiation: Specific granules develop for the particular cell type.
      • Different sets of genes are activated; lineages for the 3 types of granulocytes form.
      • Cell division ceases.
    4. Metamyelocyte: 
      • Granules are dispersed.
      • Nuclear indentation and lobulation occur.
      • Neutrophilic, basophilic, and eosinophilic metamyelocytes undergo further condensation of their nuclei.
  • Differentiation:
    • Neutrophils:
      • From the neutrophilic-metamyelocyte stage, neutrophils become band neutrophils or stab cells (intermediate stage with an elongated, not polymorphic, nucleus)
      • Segmented neutrophil: nearly mature
      • Mature neutrophil: exits to the peripheral blood
    • Eosinophils: from eosinophilic metamyelocyte → mature eosinophil
    • Basophils: from basophilic metamyelocyte → mature basophil
White Myeloid Cells

Granulopoiesis: Images depict the stages of granulocyte development.
In the most immature stage, the myeloblast is characterized by a large nucleus with faint nucleoli and a nongranular, basophilic cytoplasm.
During the promyelocyte stage, the cell enlarges and azurophilic granules appear in the cytoplasm.
In the myelocyte stage, cell division ceases and specific granules appear in the cytoplasm.
During the metamyelocyte stage, the size of the cell decreases and nuclear morphology changes; the nucleus begins to indent. For neutrophils, the nucleus forms a horseshoe shape as a band cell and is multilobulated in the mature neutrophil.
For eosinophils, the nucleus becomes bilobed and the cytoplasm has eosinophilic granules.
For basophils, the nucleus is bilobed and the cell has basic granules.

Image by Lecturio. License: CC BY-NC-SA 4.0


  • Derived from the CFU-GM (similar to neutrophils)
  • Stages:
    • Monoblast: 
      • 1st monocyte precursor
      • Round nucleus
    • Promonocyte:
      • Convoluted, indented nucleus
      • Variable basophilic granules
    • Monocyte: 
      • Lobulated, indented nucleus
      • Occasional or no granules
      • Once recruited into tissues, the cell differentiates into macrophages.
Development of monocyte

Monocyte development starts from hematopoietic stem cells (HSCs) and progresses through stages to the colony-forming unit granulocyte-macrophage (CFU-GM):
The 1st monocyte precursor is the monoblast, which has a round or oval nucleus.
The promonocyte follows and has a convoluted nucleus.
The monocyte arises with an indented nucleus and is released from the bone marrow to become a macrophage in the tissues.

Image by Lecturio. License: CC BY-NC-SA 4.0

Mast cells

  • Mast cells arise from the bone marrow: HSCs → CMP → CFU-GM → mast cell progenitor
  • Unlike other HSC-derived cells, mast cell progenitors (immature form) are released into the blood.
  • Mast cell progenitors are recruited to mucosal and epithelial tissues, undergo terminal differentiation, and become mature mast cells.

Clinical Relevance

  • Acute myeloid leukemia (AML): characterized by uncontrolled proliferation of myeloid precursor cells. Acute myeloid leukemia includes an accumulation of myeloblasts. Normal marrow is replaced by malignant cells, which leads to impaired hematopoiesis. A clinical presentation consisting of fatigue, bleeding, fever, and infection is related to anemia, thrombocytopenia, and lack of functional WBCs. Diagnosis is via peripheral blood smear and bone marrow biopsy showing myeloblasts. The precursor cells contain Auer rods. 
  • Chronic myeloid leukemia (CML): malignant proliferation of the granulocytic cell line, with a fairly normal differentiation. The underlying genetic abnormality is the Philadelphia chromosome, an abbreviated chromosome 22 resulting from reciprocal (9;22)(q34;q11) translocation. Patients can be asymptomatic, or have sternal pain and splenomegaly. Laboratory studies show elevated WBC with increased immature cells. Philadelphia chromosome demonstration by cytogenetic techniques is considered the gold standard of diagnostic testing. 
  • Chronic eosinophilic leukemia (CEL): a chronic myeloproliferative neoplasm caused by autonomous clonal proliferation of normal-appearing eosinophils, resulting in elevated eosinophils in the peripheral blood and bone marrow. The disorder is a myeloid variant of hypereosinophilic syndrome (HES) and associated with tissue infiltration, which leads to end-organ damage. Studies show an absolute eosinophilic count of ≥ 1.5 x 10⁹/L and bone marrow blasts of 5%–19%. Evidence of clonal abnormality or elevated blasts is needed for diagnosis. Without either, idiopathic HES is the appropriate term. 
  • Mastocytosis: a group of disorders with excessive accumulation of mast cells in the tissue. Cutaneous mastocytosis is limited to the skin. Systemic mastocytosis infiltrates multiple organs outside the skin. KIT mutations are a major contributing factor. Symptoms include flushing, pruritus, and chronic allergic reactions.


  1. Dahlin, J., Hallgren, J. (2015). Mast cell progenitors: Origin, development and migration to tissues. Molecular Immunology, Volume 63, Issue 1, Pages 9–17. https://doi.org/10.1016/j.molimm.2014.01.018.
  2. Espinoza, V.E., Emmady, P.D. (2021). Histology, Monocytes. StatPearls. Treasure Island (FL): StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK557618/
  3. Kuijpers T. (2021). Structure and composition of neutrophils, eosinophils, and basophils. Kaushansky K, & Prchal J.T., & Burns L.J., & Lichtman M.A., & Levi M, & Linch D.C. (Eds.), Williams Hematology, 10e. McGraw Hill. https://accessmedicine.mhmedical.com/content.aspx?bookid=2962&sectionid=252530906
  4. Mescher A.L. (Ed.). (2021). Blood. Junqueira’s Basic Histology Text and Atlas, 16e. McGraw Hill. https://accessmedicine.mhmedical.com/content.aspx?bookid=3047&sectionid=255121436

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