Activated T Cells Induce Macrophages To Produce NO and ControlLeishmania majorin the Absence of Tumor Necrosis Factor Receptor p55

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Abstract
The ability to activate macrophages in vitro for nitric oxide production and killing ofLeishmania majorparasites is dependent on tumor necrosis factor, althoughL. major-infected mice lacking the TNF receptor p55 (TNFRp55−/−mice) or both the TNFRp55 and TNFRp75 (TNFRp55p75−/−mice) are able to produce NO in vivo and eliminate the parasites. Here we report that activated T cells cocultured with macrophages results in TNFR-independent activation sufficient to control parasites and that both CD40/CD40L and LFA-1 contribute to T-cell-mediated macrophage activation. Thus, anti-CD3-stimulated T cells activated TNFR-deficient macrophages, while T cells from CD40L−/−mice were partially defective in triggering NO production by TNFRp55p75−/−macrophages. Moreover, in the presence of gamma interferon, anti-CD40 monoclonal antibody (MAb) activated TNFR-deficient macrophages. Finally, MAb blockade of LFA-1 completely inhibited macrophage NO production. Our data indicate that T cells can activate macrophages in the absence of TNF, thus providing a mechanism for how TNFR-deficient mice can control intracellular pathogens.

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