B Cell Receptor Localization

Seeing B Cell Receptors in Lipid Rafts

Science's STKE  25 Feb 2003:
Vol. 2003, Issue 171, pp. tw80-TW80
DOI: 10.1126/stke.2003.171.tw80

Biochemical analysis of lipid rafts has painted an unclear picture of their relationship with B cell receptor (BCR) function. BCR engagement with antigen or cross-linking antibodies is thought to induce receptor translocation to lipid rafts at the cell surface. These microdomains are presumably enriched with relevant downstream signaling molecules. However, studies have also shown that this translocation may only occur in mature B cells and may not involve receptor phosphorylation. But some pre-BCRs were reported to be constitutively associated with lipid rafts. Gupta and DeFranco used microscopic visualization to examine lipid rafts in live B cells. Using a fluorescent conjugate of cholera toxin B, a molecule that binds to a ganglioside enriched in lipid rafts, they observed the association of some cross-linked and activated BCRs with lipid rafts in mouse B cells. Two early signaling molecules previously implicated in B cell signaling were also identified in these microdomains upon BCR translocation--the tyrosine kinase Syk and the tyrosine phosphatase CD45, the latter of which has escaped biochemical detection in lipid rafts. Upon BCR engagement, live B cells accumulated large aggregates of lipid rafts at their cell surface and extended long thread-like filopodia, or cytonemes, enriched with lipid rafts. The images support the view that lipid rafts facilitate BCR-mediated signaling required for B cell activation and that cytonemes could participate in long-distance communication with other immune cells.

N. Gupta, A. L. DeFranco, Visualizing lipid raft dynamics and early signaling events during antigen receptor-mediated B-lymphocyte activation. Mol. Biol. Cell 14, 432-444 (2003). [Abstract] [Full Text]