CD45-associated protein is not essential for the regulation of antigen receptor-mediated signal transduction

CD45 is a transmembrane protein tyrosine phosphatase required for signaling through the T- and B-cell antigen receptors. In lymphocytes, CD45 interact s with CD45-associated protein (CD45AP), a 32 000 Mr phosphoprotein, throug h their respective transmembrane domains. To determine whether CD45AP affec ts the ability of CD45 to regulate antigen receptor signaling, CD45AP-defic ient mice were generated. Thymocyte development was grossly normal. Moreove r, the cellularity of the thymus and spleens were normal. CD45 expression o n thymocytes and splenocytes, ascertained by flow cytometry, was comparable between CD45AP-deficient mice and littermate controls. In contrast to a pr evious report (Matsuda et al., J. Exp. Med. 1998 187: 1863-1870). CD45AP-de ficient and normal thymocytes and splenocytes proliferated similarly in res ponse to various mitogens or antigen receptor cross-linking. Furthermore, t hymocyte CD45-associated p56(lck) kinase activity was similar between CD45A P-deficient and normal cells. We conclude that CD45AP is not essential for the regulation of Src-family kinase activity by CD45.