Nitric oxide-independent inhibitory effects of L-arginineanalog NG-monomethy-L-arginine on the generation of interleukin-2 activated cytotoxic activity in humans

Nitric oxide (NO) derived intracellularly from L-arginine (Arg) is indispensable for optimalgeneration of lymphokine-activated killer (LAK) cell activity in rodents. Still unclear, however, is its role in humans. To address this question human peripheral blood mononuclear cells (PBMC) from healthy donors were cultured in L-arginine free medium supplemented with recombinant interleukin-2 (rIL-2) and in the presence of exogenous L-arginine analog NG-monomethyl-L-arginine (NMMA), a specific inhibitor of the NO synthetic pathway. Cultured PBMC were tested for cytotoxic activity, proliferative capacity, and expression of phenotypic and activation markers (CD3, CD4, CD8, CD16, CD56 and CD25). Culture supernatants were assayed for nitrite (NO2−) and tumor necrosis factor-α (TNF-α) production. We found that NMMA inhibits the generation of optimal LAK cell activity when no exogenous Arg is supplied. Similar effects were also observed on proliferation, expression of IL-2 receptor induced upon rIL-2 stimulation and on TNF-α production. Sodium nitroprusside (SNP), used as a source of exogenous NO could not overcome this effect of NMMA on LAK cell activity. NO2− production was virtually undetectable in culture supernatants. Thus, NMMA affects in an NO-independent manner rlL-2 induced LAK activity in human PBMC.