Prolonging B Cell Receptor Signaling

CD19 is a coreceptor for the B cell antigen receptor (BCR) that enhances B cell response to antigen. Although it is known that activated BCRs localize to plasma membrane regions called lipids rafts, Cherukuri et al. now report that the cell-surface complex of CD19 and CD21 does so as well. The authors show that when the CD19-CD21 complex is ligated to the BCR in a B cell lymphoma cell line, the CD19-CD21 complex also translocates to lipid rafts, as determined by fractionation of cell lysates. Association with the CD19-CD21 complex in lipid rafts decreased internalization of the BCR from the cell surface and also increased phosphorylation of signaling targets of the BCR that are present in lipid rafts including Lyn. The authors suggest that interaction of the BCR with CD19 sequesters the BCR from the cellular internalization machinery, thereby allowing prolonged BCR signaling from within lipid rafts. A. Cherukuri, P.C. Cheng, H.W. Sohn, S.K. Pierce, The CD19/CD21 complex functions to prolong B cell antigen receptor signaling from lipid rafts. Immunity 14 , 169-179 (2001). [Online Journal]