The CD19/CD21 complex functions to prolong B cell antigen receptor signaling from lipid rafts

The CD19/CD21 complex functions to significantly enhance B cell antigen rec eptor (BCR) signaling in response to complement-tagged antigens. Recent stu dies showed that following antigen binding the BCR translocates into plasma membrane lipid rafts that serve as platforms for BCR signaling. Here, we s how that the binding of complement-tagged antigens stimulates the transloca tion of both the BCR and the CD19/ CD21 complex into lipid rafts, resulting in prolonged residency in and signaling from the rafts, as compared to BCR cross-linking alone. When coligated to the BCR, the CD19/CD21 complex reta rds the internalization and degradation of the BCR. The colocalization and stabilization of the BCR and the CD19/CD21 complex in plasma membrane lipid rafts represents a novel mechanism by which a coreceptor enhances BCR sign aling.