HYPERRESPONSIVE B-CELLS IN CD22-DEFICIENT MICE

CD22 is a surface glycoprotein of B lymphocytes that is rapidly phosph orylated on cytoplasmic tyrosines after antigen receptor cross-linking . Splenic B cells from mice with a disrupted CD22 gene were found to b e hyperresponsive lo receptor signaling: Heightened calcium fluxes and cell proliferation were obtained at lower ligand concentrations. The mice gave an augmented immune response, had an expanded peritoneal B-1 cell population, and contained increased serum titers of autoantibody . Thus, CD22 is a negative regulator of antigen receptor signaling who se onset of expression at the mature B cell stage may serve to raise t he antigen concentration threshold required for B cell triggering.