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B cell fate is determined by the strength of signals from the antigen receptor and from co-receptors that adjust the activation threshold and tune the B cell to its environment. These co-receptors have been broadly classified into inhibitory and enhancing groups, yet some, such as CD22, may have dual effects. CD22 recruits a variety of signal enhancers at the same time as Lyn-dependent phosphorylation leads to the binding of the inhibitory phosphatase SHP-1. To assess the relative importance of Lyn- and CD22-dependent and -independent pathways, we generated Lyn and CD22 single-deficient mice and Lyn/CD22 double-deficient mice expressing the MD4 immunoglobulin transgene against hen egg lysozyme (IgHEL). This genetic approach has enabled us to compare the contributions of Lyn and CD22 to B cell development in vivo, independent of BCR specificity and in the presence and absence of self-antigen. Our results show that although the effects of Lyn are dominant in negative regulation of B cell hyperactivity, Lyn and CD22 have independent and additive effects on B cell survival. These findings emphasize the subtle nature of regulation at the BCR and the usefulness of genetic complementation to dissect common and parallel pathways.

Original publication




Journal article


Eur J Immunol

Publication Date





3655 - 3663


Animals, B-Lymphocytes, Cell Differentiation, Cell Survival, Cells, Cultured, Immune Tolerance, Mice, Mice, Inbred C57BL, Mice, Knockout, Mice, Transgenic, Receptors, Antigen, B-Cell, Sialic Acid Binding Ig-like Lectin 2, src-Family Kinases