3.3.1

HUMORAL RESPONSE

3.3.1.1

B-Cells

B-cells recognize soluble antigens. However, not all B cells can recognize every

antigen. At birth, everyone possesses a large number of naïve B-cells. They are

called naïve because they have not been exposed to any antigen yet. Each one of

these naïve B-cells produces a specific antibody and therefore recognizes only a

specific antigen. If a naïve B cell is exposed to its target antigen, antigen-antibody

binding triggers a series of events that results in the proliferation and expansion

of this specific B-cell. This is called the clonal selection theory, and this is how

the body generates its repertoire of antibodies, each one recognizing a specific

antigen. As shown in Figure 3.6, when lymph-carrying soluble antigen enters

the lymph node, B-cells are exposed to these antigens, and the B-cell that re-

cognizes that particular antigen, migrates to the follicle where clonal expansion

takes place.

FIGURE 3.5 Lymphatic system. The cell-free liquid part of blood is transported out of

blood vessels and bathes tissues, providing nourishment and removing waste matter. This

liquid returns to the circulation via the open ends of lymph vessels, which then deliver lymph

to lymph nodes. The primary lymphoid organs where lymphocytes are generated are the bone

marrow (B cells) and thymus (T cells).

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