Regulation of growth and differentiation of human B cells

Activation process of B lymphocytes into immunoglobulin (Ig)-secreting cells can be dissected into three steps, i.e., activation, proliferation and differentiation (1–3). It has been demonstrated by several investigators that B cell specific growth and differentiation factors are involved in the process of proliferation and differentiation of activated B cells (4–10). The presence of two different kinds of B cell growth factors, BCGF-I or BSF-pI and BCGF-II, was reported in human (11) as well as in murine systems (12). BCGF-I induces proliferation of anti-IgM-stimulated human or murine B cells as well as SAC (Staphylococcus aureus Cowan I)-stimulated human B cells. Activated but not resting B cells are able to adsorb the activity of BCGF-I, suggesting the induction of the expression of receptors for BCGF-I on activated B cells. However, a recent study showed an increased expression of Ia antigen on resting B cells by stimulation with BCGF-I, suggesting the presence of BCGF-I receptors even on resting B cells, although BCGF-I induces proliferation only in activated B cells (13).