Negative regulation of antigen receptor signaling in lymphocytes.

The negative regulation of antigen receptor signal transduction is essential for the maintenance of thresholds for activation in lymphocytes. CD45 and SHP-1 are tyrosine phosphatases that are important in maintaining the proper level of tyrosine phosphorylation. Regulation of the src family of tyrosine kinases is mediated by the coordinated action of the tyrosine kinase Csk and the tyrosine phosphatase CD45. B cell receptor signaling is negatively regulated by the recruitment of SHP-1 to bind the B cell transmembrane proteins CD22 and FcgammaRIIb1. SHP-1 also functions to negatively regulate T cell receptor signaling by dephosphorylating and inactivating tyrosine kinases.