Involvement of tumor necrosis factor-alpha during infection of human monocytic cells by Toxoplasma gondii

Although the involvement of tumor necrosis factor-alpha (TNF-alpha) during Toxoplasma gondii infection has largely been described in mouse models, onl y a few studies in human models have been reported. We demonstrated the rol e of TNF-alpha during the process of invasion by T. gondii in human monocyt ic cells. Cotreatment of cells with interferon-gamma (IFN-gamma) and lipoly saccharide (LPS) during T. gondii infection induced TNF-alpha production an d decreased the number of parasitized cells (invasion index). Neutralizatio n of the production of TNF-alpha using a specific monoclonal antibody or pe ntoxifylline enhanced the invasion index. The relationship between TNF-alph a production and protection of monocytic cells against T. gondii invasion w as confirmed by treatment of infected cultures with exogenous TNF-alpha. Th us, in contrast to the results obtained in murine models but in accordance with those observed in other human models, the present study shows for the first time in human monocytic cells that T. gondii does not induce any TNF- alpha secretion and inhibits TNF-alpha production induced by IFN-gamma/LPS.