Answer to Question #195538 in Cell Biology for Ivy

Question

Evaluate the clonal selection hypothesis in terms of autoimmunity and

immunological memory.

Answer 1

Clonal selection is the theory that lymphocytes have antigen receptors before they are activated, and that spontaneous mutations during clonal expansion lead to lymphocytes with high antigen-binding affinities. It is a theory that a single lymphocyte (specifically, a B cell) expresses antigen-specific receptors that are determined before the antibody ever meets the antigen. As Ag binds to a chromosome, it stimulates it, allowing clone daughter cells to proliferate.

Negative selection in the bone marrow produces central tolerance in B cells. Before leaving the bone marrow, immature B cells are screened for auto-reactivity. Immature B cells with BCRs that bind to self-antigens too strongly will not be destroyed. Random mutations during clonal expansion induce the development of B cells with an improved antibody-binding affinity for their antigens during clonal selection. The clonal selection hypothesis could understand why secondary immune responses are so effective in avoiding reinfection by the same pathogen.