The role of CD40 in the regulation of humoral and cell-mediated immunity.

The dynamic and reciprocal communication between T helper (Th) cells and B cells appears to rely on the provision of multiple signals. The first is antigen specific and is mediated by the interaction between the T-cell receptor (TCR) and antigen bound to the major histocompatibility complex (MHC). The subsequent signals are provided by the binding of accessory molecules such as CD28 and CD40 to their respective ligands. Here, Fiona Durie and colleagues discuss the co-stimulatory role of the interaction between CD40 on B cells and CD40 ligand (CD40L, gp39) on T cells, and review evidence that suggests blocking this interaction may induce T-cell tolerance.