Cross-linking of CD45 enhances activation of the respiratory burst in response to specific stimuli in human phagocytes.

The phosphotyrosine phosphatase CD45 is expressed on the surface of all leukocytes and is known to play a critical role in the regulation of both T and B cell function. In contrast, relatively little information exists regarding the role of CD45 in the phagocyte lineage. We present evidence that CD45 modulates activation of the inducible respiratory burst in normal human neutrophils, monocytes, and eosinophils, as measured by luminol-enhanced chemiluminescence. In neutrophils, the respiratory burst induced by FMLP (1 microM), granulocyte-macrophage CSF (GM-CSF; 1 microgram/ml), or TNF-alpha (100 U/ml) was enhanced synergistically by CD45 cross-linking. This effect was most striking upon stimulation 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 microgram/ml), IFN-gamma (100 U/ml), or granulocyte CSF (1 microgram/ml) was not affected significantly by CD45 cross-linking. Similar results were obtained by using iodination for measurement of the respiratory burst. In monocytes, CD45 cross-linking significantly increased chemiluminescence stimulated by FMLP, GM-CSF, TNF-alpha, and LPS, and GM-CSF- and TNF-alpha-induced chemiluminescence was enhanced significantly by cross-linking of CD45 on eosinophils. Immunoblot analysis demonstrated that both the rate and intensity of TNF-alpha-induced tyrosine phosphorylation were increased by CD45 cross-linking in neutrophils. Major tyrosine-phosphorylated products include proteins with approximate molecular masses of 40 kDa, 70 kDa, 78 kDa, and 110 kDa. These results provide direct evidence that CD45 is capable of regulating the inducible respiratory burst in human phagocytes. On the basis of our findings, we postulate that CD45 may mediate coupling of specific cell surface receptors to downstream tyrosine kinase-dependent signal-transduction pathway(s) in activated phagocytes.