Dual antigen recognition by B cells.

Foreign antigens opsonized by complement degradation products may be bound by both the B-cell antigen receptor (BCR) and CR2-CD19 complexes. Under these circumstances, the extensive cytoplasmic tail of CD19 endows the BCR with additional tyrosine kinase activity and with potential docking sites for molecules involved in cell signalling. Here, Carel van Noesel and colleagues argue that cooperation between BCR and CR2-CD19 at both the extra- and intracellular level provide for optimal recognition of antigen and amplification of ensuing intracellular signals.