Selection of the B cell repertoire by self antigens

Once slg-positive cells have been generated they are subjected to selection processes by self antigens in their own environment, probably presented by cells in the B cell-generating organs. Self reactive B cells appear to be either deleted or anergized. Whether positive selection for self antigens can also occur -maybe in a special B lineage, the Ly-1+/CD5 ' B cells -needs to be elucidated.

Those B cells which have been untouched by these selection processes then enter the mature B cell compartment of virgin cells involved in primary B cell responses. Such cells still turn over rather rapidly, with half-lives of less than 1 week. They can be stimulated by foreign antigens, either with the help of T cells (helper T cell dependent) or without such help (T cell independent). Stimulation results in the activation from a resting, G0 state and entry into the proliferative cell cycle. One cell cycle lasts 20 hours at 37°C and is controlled by several interactions (see below) of antigen, helper T cells, accessory cells and cytokines. Proliferating B cells also mature to Ig-secreting cells. A single activated B cell can balance between proliferation and maturation to Ig secretion. With every successive cell cycle the contribution to Ig secretion increases, so that finally mature plasma cells develop which no longer divide.

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