DETECTION OF RESTRICTED ISOFORM EXPRESSION AND TYROSINE PHOSPHATASE-ACTIVITY OF CD45 IN MURINE DENDRITIC CELLS

CD45 is a cell surface transmembrane tyrosine phosphatase. It is expre ssed as distinct protein isoforms via alternative splicing of exons 4, 5 and 6. In T and B lymphocytes, CD45 is thought to play a critical r ole in antigen-dependent signaling through their respective antigen re ceptor complexes. However, the isoform expression and enzymatic activi ty of CD45 in other leukocytes remains largely unknown. Here, we exami ne the isoform expression and phosphatase activity of CD45 in murine d endritic cells (DC). Flow cytometric double-labeling analysis and bioc hemical analysis of purified splenic DC CD45 demonstrate that DC expre ss both the CD45RB and CD45R0 isoforms. Flow cytometric analyses of fr eshly isolated splenic DC and thymic DC also indicate the expression o f CD45RB and CD45R0 on these DC populations. In addition, we find that purified splenic DC CD45 possesses a high level of intrinsic tyrosine phosphatase activity. These data therefore establish the restricted i soform expression pattern of CD45 in murine DC and demonstrate that ce lls lacking specific antigen receptor complexes have active tyrosine p hosphatase activity associated with CD45.