Activation of B lymphocytes: integrating signals from CD19, CD22 and FcγRIIb1

Three accessory membrane proteins, CD19, CD22 and FcγRIIb1, alter signaling through membrane immunoglobulin of B cells by binding cytosolic proteins containing SH2 domains. Recent biochemical and genetic studies have shown that these receptors enable B cells to amplify responses to certain T-cell-dependent antigens (CD19), to restrict their response to T-cell zones of secondary lymphoid organs (CD22), and to dampen their responses to antigens for which IgG is already available (FcγRIIb1).