The effect of NG-monomethyl-L-arginine(LNMMA), an NO-synthase blocker on the survival of intracellular BCG within human monocyte-derived macrophages.

Human peripheral blood monocytes are permissive for the growth of Mycobacterium bovis (BCG), but the fate of nonpathogenic Mycobacterium bovis in these cells is not clearly known. Both oxidative and nonoxidative pathways have been implicated in killing of intracellular mycobacteria. Since human monocytes are not so far confirmed to release Reaction Nitrogen Intermediates (RNI), we tried indirect approach to inhibit the production of NO by the addition of NG-monomethyl-L-arginine (LNMMA)-an NO synthase blocker, in the infected cell cultures. In our studies adherent human peripheral blood monocytes were found to be permissive for the growth of Mycobacterium bovis, as measured by [3H] uridine uptake and confirmed by Colony Forming Unit (CFU) estimate. The killing of Mycobacterium bovis was not blocked by LNMMA, suggesting that it was not due to the production of Reactive Nitrogen Intermediates. Culture of the monocyte-derived macrophages for 1 to 14 days before infection had no effect on the fate of Mycobacterium bovis, and no nitric oxide was detected in the culture supernatants of these infected cell cultures. Graded doses of sodium nitrite at physiological concentrations however failed to affect cell free cultures of Mycobacterium bovis. These findings suggest that the addition of NG-monomethyl-L-arginine (LNMMA), an antagonist of L-arginine oxidation and inhibitor of NO production, had no effect on the fate of Mycobacterium bovis in human monocytes and macrophages.