Regulation of immune function by protein tyrosine phosphatases.

CD45 is a leukocyte transmembrane protein tyrosine phosphatase that functions in lymphocyte activation by increasing the kinase activity of Src family members. In contrast, an intracellular protein tyrosine phosphatase that contains Src homology 2 domains, SHP, is required to inactivate receptors. Recent studies have examined the mechanisms of interaction and regulation of these enzymes.