ANALYSIS OF THE IN-VITRO EFFECT OF EXOGENOUS NITRIC-OXIDE ON HUMAN-LYMPHOCYTES

We investigated the role of endogenous or exogenous nitric oxide (NO) on human lymphocyte function. We used sodium nitroprusside, nitroglyce rine, S-nitroso-N-acetylpenicillamine, sodium nitrite and S-nitroso-L- glutathione as NO-generating compounds. All agents were used at doses that do not produce direct cytotoxicity as measured by trypan blue exc lusion as well as chromium-51 release assay. The immune responses exam ined were peripheral blood lymphocytes (PBL) proliferation and IL-2 pr oduction after activation with OKT3 and PHA; allogeneic mediated proli feration and cell mediated cytotoxicity (CML) in MLR; IgG and IgM prod uction after PBL activation with Con-A; proliferation and expression o f IFN-gamma and IL-4 mRNA after activation of allogeneic CD4+T cell cl ones. Cytokine mRNA expression was measured by reverse transcriptase P CR. Our results show that proliferating lymphocytes do not produce a d etectable amount of NO as measured by the Griess reaction. In separate experiments, the addition of N-G-monomethyl-L-arginine (L-NMMA) did n ot affect lymphocyte proliferation. Sodium nitroprusside and nitroglyc erine exerted a dose dependent antimitogenic effect, inhibited cytokin e production and expression, CML generation and antibody production. D NA gel electrophoresis showed no evidence for enhanced programmed cell death. The antimitogenic effect could not be blocked by the NO scaven gers, hemoglobin or methylene blue. In contrast, the other nitric oxid e generating compounds did not inhibit lymphocyte mitogenesis. The res ults suggest that human lymphocytes do not produce appreciable amounts of NO to affect lymphocyte mitogenesis. Sodium nitroprusside and nitr oglycerine have a potent but nonspecific immunoinhibitory effect on hu man lymphocyte function by a mechanism other than NO production. In ad dition, pharmacological levels of NO do not inhibit human lymphocyte m itogenesis.