CROSS-LINKING OF CD45 ENHANCES ACTIVATION OF THE RESPIRATORY BURST INRESPONSE TO SPECIFIC STIMULI IN HUMAN PHAGOCYTES

The phosphotyrosine phosphatase CD45 is expressed on the surface of al l leukocytes and is known to play a critical role in the regulation of both T and B cell function. In contrast, relatively little informatio n exists regarding the role of CD45 in the phagocyte lineage. We prese nt evidence that CD45 modulates activation of the inducible respirator y burst in normal human neutrophils, monocytes, and eosinophils, as me asured by luminal-enhanced chemiluminescence. In neutrophils, the resp iratory burst induced by FMLP (1 mu M), granulocyte-macrophage CSF (GM -CSF; 1 mu g/ml), or TNF-alpha (100 U/ml) was enhanced synergistically by CD45 cross-linking. Th is effect was mast striking upon stimulatio n with TNF-alpha, in which cross-linking of CD45 resulted in a 30-fold increase in chemiluminescence. Chemiluminescence induced by PMA (100 nM), opsonized zymosan (1 mg/ml), LPS (1 mu g/ml), IFN-gamma (100 U/ml ), or granulocyte CSF (1 mu g/ml) was not affected significantly by CD 45 cross-linking. Similar results were obtained by using iodination fo r measurement of the respiratory burst. In monocytes, CD45 cross-linki ng significantly increased chemiluminescence stimulated by FMLP, GM-CS F, TNF-alpha, and LPS, and GM-CSF- and TNF-alpha-induced chemiluminesc ence was enhanced significantly by cross-linking of CD45 on eosinophil s. Immunoblot analysis demonstrated that both the rate and intensity o f TNF-alpha-induced tyrosine phosphorylation were increased by CD45 cr oss-linking in neutrophils. Major tyrosine-phosphorylated products inc lude proteins with approximate molecular masses of 40 kDa, 70 kDa, 78 kDa, and 110 kDa. These results provide direct evidence that CD45 is c apable of regulating the inducible respiratory burst in human phagocyt es. On the basis of our findings, we postulate that CD45 may mediate c oupling of specific cell surface receptors to downstream tyrosine kina se-dependent signal-transduction pathway(s) in activated phagocytes.