B cells are lymphocytes which have matured in the bone marrow. They comprise approximately 25% of the lymphocyte population. They are precursors of plasma cells, and once triggered by antigen bound to MHC class II molecules on the surface of an antigen presenting cell, they are stimulated to divide and to secrete antibody. These antibodies, or immunoglobulins as they are also known, are proteins with sites that specifically bind the triggering antigen.
- B cells express IL-2 receptors and proliferate in response to IL-2. They are the predominant cell type in the primary germinal follicles of lymph nodes. B cells tend to remain in lymphoid tissue
- B cells can be distinguished by the presence of CD19 and CD20 molecules as well as surface immunoglobulin. The latter can be detected by using fluorescent labelled anti - immunoglobuli.
- B cells have a shorter life cycle than T cells; days rather than months
- not all proliferating B cells develop into plasma cells - a significant proportion remain as memory B cells through a process known as clonal selection
- process is vital in eliminating the antigen should the body become re-exposed to it in the future
- T and B cells both are able to recirculate around the body migrating from blood to tissue and vice versa
- ability to recirculate increases the efficiency with which cells of the immune system can home onto the invading antigen