Lymphokines active in B cell proliferation and differentiation.

Activation of B cells from a resting to an Ig-secreting cell is a multistep event regulated by T cells and their products. These steps include (1) induction of the clonally selected B cell, (2) growth, and (3) maturation of the proliferating cell to Ig secretion. In model systems, induction can be achieved either by direct signalling to the B cells by T cells recognizing surface structures without Ig involvement or, alternatively, via Ig only. Under physiologic conditions a cooperativity of the two events is assumed. Following induction, B cells are supposed to express receptors for growth and maturation factors produced by the neighboring T cell. Growth and differentiation are mediated by distinct molecules.