A decade has passed since monoclonal antibodies allowed the identification of the CD40
antigen. Meanwhile it has become clear that, in addition to soluble factors (cytokines), direct
cellular interactions play a pivotal role in the regulation of immune responses. The CD40
antigen was independently identified in 1985 and 1986 by monoclonal antibodies reacting
with carcinomas and B cells (antibody S2C6, antigen p50 (Paulie et al., 1985)) and showing
costimulatory effects for B lymphocyte proliferation (antibody G28-5, antigen Bp50 (Clark …