Effect of tumor necrosis factor on growth of Trypanosoma musculi in vivo and in vitro.

The effect of r-TNF on T. musculi is complex. When trypanosomes are incubated in culture with this monokine, TNF exerts a direct anti-trypanosomal effect (Table 3). Similarly, if mice are treated with TNF during the later stages of infection, after the parasitaemia has stabilized, it hastens the elimination of the trypanosomes (Table 2). When TNF is given to mice from the early stage of infection onwards, it enhances the growth of the parasites (Table 1). (This enhanced early growth probably masks any subsequent anti-trypanosomal effect of TNF exerted later in infection). The ability of TNF to promote parasite multiplication is observed even more clearly in in vitro experiments, when peritoneal exudate cells are added to the T. musculi cultures (Table 4). It is conceivable, therefore, that the enhancing effect of TNF in vivo is mediated via a cell present in thioglycollate-induced peritoneal exudate, which mostly comprises macrophages. In summary, the results of these experiments suggest that r-TNF exerts a direct anti-trypanosomal effect while simultaneously promoting the growth of the parasite through an indirect effect mediated via the host's cells, possibly the macrophages.