MODULATION OF HUMAN NEUTROPHIL INFLAMMATORY RESPONSES BY NITRIC-OXIDE- STUDIES IN UNPRIMED AND LPS-PRIMED CELLS

Because nitric oxide (NO) can act both as a regulatory and as a toxic molecule, we have studied N-formyl-methionyl-leucyl-phenylalanine (fML F) -stimulated responses of human neutrophils (PMNs) during various co nditions of NO modulation in unprimed and bacterial lipopolysaccharide (LPS) -primed cells, Effects of various NO modulators were assessed o n stimulated superoxide (O-2(-)) generation, granule exocytosis, homot ypic aggregation, and rises in intracellular free Ca2+ ([Ca2+](i)), Si gnificant differences in the effects of various NO modulators on infla mmatory responses of PMNs kept in stirred suspension versus those kept under static and/or adherent conditions, were observed, L-arginine, t he physiological substrate for NO synthase (NOS), and N-G-nitro-L-argi nine methyl ester, an inhibitor of NOS, both caused a 40-50% inhibitio n of LPS-induced priming of O-2(-) generation in PMNs in stirred suspe nsion, but not in LPS-primed PMNs under static or adherent conditions, The NO donors, sodium nitroprusside and S-nitroso-N-acetylpenicillami ne, completely abrogated the LPS-induced priming of O-2(-) generation in PMNs in suspension, while causing only a 40-50% inhibition in PMNs under static or adherent conditions, The Ca2+ ionophore, A23187, preve nted the LPS-induced priming of O-2(-) generation without affecting O- 2(-) generation in unprimed PMNs. LPS priming of PMNs induced about a twofold increase in fMLF-stimulated homotypic aggregation, exocytosis of secondary granules, and rises in [Ca2+](i). In related studies, we also provide definitive evidence for enzymatic formation of NO in huma n PMNs and demonstrate a significant decrease in NO levels in LPS-prim ed PMNs. Taken together, these findings indicate that NO modulates PMN inflammatory responses and plays a protective role in printing and ac tivation processes of inflammatory PMNs.