Beta interferon inhibits Toxoplasma gondii growth in human monocyte-derived macrophages.

Gamma interferon (IFN-gamma) previously has been shown to block the replication of Toxoplasma gondii in fibroblasts by the induction of indoleamine 2,3-dioxygenase (IDO) activity. IFN-beta also is known to induce IDO activity in monocyte-derived macrophages, but its ability to block the growth of T. gondii has not been demonstrated. We found not only that the combination of IFN-beta and lipopolysaccharide induced greater IDO activity in monocyte-derived macrophages than did IFN-beta alone but that this combination also was effective in inhibiting the growth of T. gondii. In addition, the inhibition was reversed by the addition of exogenous tryptophan, thus demonstrating that a mechanism by which IFN-beta inhibited T. gondii replication was by the induction of IDO.