MACROPHAGE INFLAMMATORY PROTEIN-1-ALPHA PRODUCTION IN LIPOPOLYSACCHARIDE-STIMULATED HUMAN ADHERENT BLOOD MONONUCLEAR-CELLS IS INHIBITED BY THE NITRIC-OXIDE SYNTHASE INHIBITOR N-G-MONOMETHYL-L-ARGININE

The release of chemokines such as macrophage-inflammatory protein-1 al pha or (MIP-1 alpha) from activated macrophages is a crucial step in c ell recruitment necessary for establishing local inflammatory response s, To ascertain the importance of the L-arginine/nitric oxide (NO) pat hway in LPS-induced MIP-1 alpha release, we stimulated human adherent PBMC with LPS in the presence of the NO synthase inhibitor N-G-monomet hyl-L-arginine (L-NMMA). L-NMMA decreased LPS-induced MIP-la protein r elease (45.5% inhibition) and steady state levels of mRNA (48% inhibit ion) in adherent PBMC, The concentration of L-NMMA for inhibition of M IP-1 alpha release was dependent on the concentration of L-arginine in the cell culture medium, emphasizing the L-arginine-related action of the drug, Most of the MIP-1 alpha release was attributed to the activ ity of IL-l and TNF, since coincubation of LPS-stimulated PBMC with IL -1R antagonist and TNF-binding protein abrogated LPS-induced MIP-1 alp ha release (by 76.8%). Analysis of cytokine secretion revealed that, i n addition to MIP-1 alpha, L-NMMA inhibited the release of mature IL-1 beta (by 70%) and TNF-alpha (by 53%). In contrast, release of macroph age chemoattractant protein-1 was unaffected; IL-10 was augmented (123 .4%) by L-NMMA. In the presence of exogenous NO provided by NO donors, LPS-induced MIP-1 alpha release was enhanced, We concluded that endog enous NO acts as a mediator of inflammation, Since IL-10 is a potent a nti-inflammatory cytokine, these data also suggest that L-NMMA acts as an anti-inflammatory agent by specifically altering the balance of pr o-and antiinflammatory cytokines released from LPS-stimulated human PB MC.