Interferon-gamma- and lipopolysaccharide-induced tumor necrosis factor-alpha is required for nitric oxide production: Tumor necrosis factor-alpha andnitric oxide are independently involved in the killing of Mycobacterium microti in interferon-gamma- and lipopolysaccharide-treated J774A.1 cells

A comparative study was done using J774A.1 and J774A.1-derived transfected cells (J774A.1 C.1) containing antisense tumor necrosis factor alpha (TNF-a lpha) plasmid to determine the role of endogenous TNF-alpha on nitric oxide production as well as on the growth of Mycobacterium microti in interferon gamma (IFN-gamma)- and lipopolysaccharide (LPS)-treated cells. On stimulat ion with IFN-gamma and LPS a higher level of NO was observed in J774A.1 cel ls compared to J774A.1 C.1 which indicated that endogenous TNF-alpha is req uired for the production of NO. Comparing the effect of IFN-gamma and LPS o n the intracellular growth of M. microti, the growth-reducing activity was higher in J774A.1 cells than in J774A.1 C.1 cells and was not completely ab rogated in the presence of the nitric oxide inhibitor N-G-methyl-L-arginine (L-NMA). J774A.1 C.1 cells infected with M microti produced a significant amount of NO when exogenous TNF-alpha was added along with IFN-gamma and LP S and the concentration of intracellular bacteria decreased almost to that in IFN-gamma and LPS treated parental J774A.1 cells. Addition of exogenous TNF-alpha even in the presence of L-NMA in J774A.1 C.1 cells could also par tially restore intracellular growth inhibition of M. microti caused by IFN- gamma and LPS. TNF-alpha is probably required for the production of NO in J 774A.1 cells by IFN-gamma and LPS but TNF-alpha and NO are independently in volved in the killing of intracellular M. microti with IFN-gamma and LPS.