[Tumor necrosis factor (TNF) and oxygen free radicals: potential effects for immunity]

During various biological processes as inflammation or septic shock, free radical damages are produced by a direct production of oxygen radicals by phagocytes, but also by a TNF-mediated generation in target cells. Antioxidants have been demonstrated as protective against TNF cytotoxicity. We try to measure directly the free radical produced by murine recombinant TNF on L929 cells, by detecting the direct light produced by decomposition of superoxide using an adapted chemiluminometer. We measure also the chemiluminescence after addition of luminol. These techniques demonstrate the effective production of oxygen radicals. Unfortunately they have a rather poor specificity and sensitivity. So we use the protective effect of antioxidants on cytotoxicity to investigate the origin of the productive mechanism. We evaluate cytotoxicity of 1 U/ml TNF on L929 murine fibroblasts after 24 hours incubation with actinomycin D by the MTT and Cr51 release. Using the MTT test we observe that addition of thiourea or catalase has the better protecting effect when Zu-Zn SOD had few effect. Reversely using the Cr51 release we observe a good protective effect of Cu-Zn SOD simultaneously with a good protective effect of catalase. So the difference in the effect of various antioxidant agent do not permit to identify the species generated, but depend more on the ability of the antioxidant to reach the cell compartment tested by the method (membrane, or mitochondria). The oxidative effect of TNF is beneficial in physiological condition to destroy cancerous or virus infested cells infested by virus inside the body. But this effect can be deleterious in situation of deficiency in some antioxidant. TNF-induced free radicals can increase the replication of virus as HIV-1 and destroy immunocompetent cells as T cells. This last action explains the defect in cellular immunity observed in oxidative stress and the immunostimulatory effect of many antioxidants.