CD40 LIGAND AND ITS ROLE IN X-LINKED HYPER-IGM SYNDROME

CD40 ligand (CD40L) on activated T cells binding to CD40 on B cells is of critical importance for Ig heavy-chain switching and rescue of B c ells from apoptosis after somatic mutation in the germinal centre. Mut ations in the CD40L gene are now known to cause X-linked hyper-IgM syn drome (HIGM1), an immunodeficiency characterized by the absence of ser um IgG, IgA and IgE. In this review, we discuss bow basic and clinical immunology have combined to provide major insights into the function of CD40 in T-B cell collaboration.