NITRIC OXIDE-INDEPENDENT INHIBITORY EFFECTS OF L-ARGININE ANALOG N-G-MONOMETHY-L-ARGININE ON THE GENERATION OF INTERLEUKIN-2 ACTIVATED CYTOTOXIC ACTIVITY IN HUMANS

Nitric oxide (NO) derived intracellularly from L-arginine (Arg) is ind ispensable for optimal generation of lymphokine-activated killer (LAK) cell activity in rodents. Still unclear, however, is its role in huma ns. To address this question human peripheral blood mononuclear cells (PBMC) from healthy donors were cultured in L-arginine free medium sup plemented with recombinant interleukin-2 (rlL-2) and in the presence o f exogenous L-arginine analog N-G-monomethyl-L-arginine (NMMA), a spec ific inhibitor of the NO synthetic pathway. Cultured PBMC were tested for cytotoxic activity, proliferative capacity, and expression of phen otypic and activation markers (CD3, CD4, CD8, CD16, CD56 and CD25). Cu lture supernatants were assayed for nitrite (NO2-) and tumor necrosis factor-alpha (TNF-alpha) production. We found that NMMA inhibits the g eneration of optimal LAK cell activity when no exogenous Arg is suppli ed. Similar effects were also observed on proliferation, expression of IL-2 receptor induced upon rlL-2 stimulation and on TNF-alpha product ion. Sodium nitroprusside (SNP), used as a source of exogenous NO coul d not overcome this effect of NMMA on LAK cell activity. NO2- producti on was virtually undetectable in culture supernatants. Thus, NMMA affe cts in an NO-independent manner rlL-2 induced LAK activity in human PB MC.