Central role of CD40 and its ligand in B lymphocyte responses to T-dependent antigens.

In order to mount an effective antibody response to soluble and certain other types of antigens, B cells need help from T cells. Recently, an important receptor-ligand pair has been identified as essential for successful cognate interaction between these two classes of lymphocytes. CD40 was first identified as a receptor-like molecule on B cells which when ligated by antibody could deliver signals to prime for growth, differentiation, or survival. Later its counterstructure--termed CD40 ligand (CD40L)--was discovered to be an inducible type II glycoprotein of helper T cells. In this review, the central role of the CD40-CD40L interaction in the various phases of the B cell response to T-dependent antigens is discussed drawing from both in vitro and in vivo studies.