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T-Dependent, T-Independent Antigens and Class Switching – Humoral Immunity

by Peter Delves, PhD
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    The term T-dependant antigen is used to denote the fact that most B-cell responses require assistance from helper T-cells. So an antigen will be taken up by a dendritic cell, it’ll be processed and presented to a naïve T helper cell. This T helper cell will then interact with B lymphocytes and cause their proliferation and differentiation into plasma cells. These plasma cells will go on and secrete a soluble version of the antibody molecule. The interaction of the helper T-cell with the B-cell can be facilitated by the fact that the B-cell itself can act as a professional antigen presenting cell for antigen experienced T helpers. In other words, dendritic cells are required to activate naïve T-cells, but once they have been activated by a dendritic cell, the B-cell can take over that function of acting as a professional antigen presenting cell; showing peptides to the T-cell receptor on the helper T-cell. However some antigens are T-independent antigens with respect to the B-cell response. These are antigens that tend to have repeating structures which extensively cross-link the B-cell receptor or cross-link Pattern Recognition Receptors and the B-cell receptor together. But because T-cells do not participate in the response to these T-independent antigens, there is no class switching and only IgM is produced. Because in order to get class switching to IgG or IgA or IgE production, you need CD40 ligand on the surface of the T-cell to interact with CD40 on the surface of the B-cell. And if there’s no T-cell involved, then that class switching will not occur. Examples of T-independent antigens include bacterial lipopolysaccharide, capsular polysaccharides of bacteria and polymeric proteins. So here we can see a T-independent antigen with multiple repeating structures on its surface, powerfully cross-linking the B-cell receptor on the surface of the B-lymphocyte....

    About the Lecture

    The lecture T-Dependent, T-Independent Antigens and Class Switching – Humoral Immunity by Peter Delves, PhD is from the course Humoral Immunity and Cell-Mediated Immunity. It contains the following chapters:

    • T-Dependent Antigens
    • T-Independent Antigens
    • Class Switching

    Included Quiz Questions

    1. CD40L on the surface of a T-cell
    2. CD40L on the surface of a B-cell
    3. CD80 on the surface of a B-cell
    4. CD28 on the surface of a T-cell
    5. CD3 on the surface of a B-cell
    1. Antigen experienced T cells
    2. Naive T cells
    3. Naive B cells
    4. Dendritic cells
    5. Plasma cells
    1. The antigen is T independent
    2. The antigen only activates T cells, not B cells
    3. The antigen stimulates class switching
    4. The antigen must be of viral origin because bacterial pathogens do not possess antigens that exhibit this property
    5. The antigen is not recognized by Pattern Recognition Receptors

    Author of lecture T-Dependent, T-Independent Antigens and Class Switching – Humoral Immunity

     Peter Delves, PhD

    Peter Delves, PhD


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