B-cell clonal selection and proliferation

It is evident from the examples describing immunoglobulin and TcR structures that only a few residues of each protein molecule are crucial for the recognition process. The remainder of the structure of the molecule, the receptor, or the antigen-presenting protein is involved in other functions, including localization by other cell surface proteins. 

Stimulation of B cells to proliferate, differentiate, and synthesize antibodies occurs through signals provided by molecules synthesized and secreted by T cells. These signaling molecules, the cytokines and particularly the interleukins, are described in Table 35-4. 

The critical importance the CD4+ T cells and their messenger molecules for B-cell proliferation is manifest in AIDS where HIV proteins promote death of CD4+ T cells resulting in inadequate stimulation of B-cell proliferation. One of the early clues to this action of HIV was the change in the ratio of CD4 to CD8 cells in AIDS patients. The CD4+ cell count and the CD4/CD8 ratio quickly became markers for the progression of the disease. The immunodeficiency that results from destruction of Th cells 

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