The CD19-CR2-TAPA-1 complex, CD45 and signaling by the antigen receptor of B lymphocytes.

A paradigm describing the response of T lymphocytes to antigen holds that signals from antigen receptors must be modulated by non-antigen-specific, accessory membrane proteins for an appropriate cellular response to occur, such as differentiation, activation and tolerance. Recent studies suggest that this paradigm applies also to B lymphocytes. Signaling through membrane IgM in these cells requires CD45, a phosphotyrosine phosphatase, and is amplified by a complex containing CD19, complement receptor 2 (CD21), and TAPA-1, which recruits the intracellular enzyme, phosphatidylinositol 3-kinase.