INHIBITION OF LEGIONELLA-PNEUMOPHILA GROWTH BY GAMMA-INTERFERON IN PERMISSIVE A J MOUSE MACROPHAGES - ROLE OF REACTIVE OXYGEN SPECIES, NITRIC-OXIDE, TRYPTOPHAN, AND IRON(III)/

A/J mouse macrophages infected with Legionella pneumophila and treated with gamma interferon (IFN-gamma) in vitro developed potent antimicro bial activity. This antilegionella activity was independent of the mac rophage capacity to generate reactive oxygen intermediates, since the oxygen radical scavengers catalase, superoxide dismutase, mannitol, an d thiourea had no effect on the antilegionella activity of IFN-gamma-a ctivated macrophages. Likewise, whereas the ability of IFN-gamma-activ ated macrophages to synthesize reactive nitrogen intermediates was mar kedly inhibited by the L-arginine (Arg) analogs, N-G-monomethyl-L-argi nine and L-aminoguanidine, as well as by incubation in L-Arg-free medi um, their ability to inhibit the intracellular growth of L. pneumophil a remained intact. The intracellular growth oft. pneumophila in A/J ma crophages was inhibited by the iron(III) chelator desferrioxamine and reversed by Fe-transferrin as well as by ferric salts. Additionally, I FN-gamma-activated macrophages incorporated 28% less Fe-59(III) compar ed, with nonactivated cells. Nonetheless, only partial blocking of gro wth restriction was observed when IFN-gamma-stimulated macrophages wer e saturated with iron(III). Indole-propionic acid, which appears to in hibit the biosynthesis of L-tryptophan (L-Trp), was an L-Trp-reversibl e growth inhibitor oft. pneumophila in macrophages, implying that the intracellular replication of this pathogen is also L-Trp dependent. Ho wever, an excess of exogenous L-Trp did not reverse the growth inhibit ion due to IFN-gamma, though a small synergistic effect was observed w hen the culture medium was supplemented with both iron(III) and L-Trp. We conclude that IFN-gamma-activated macrophages inhibit the intracel lular proliferation of L. pneumophila by reactive oxygen intermediate- and reactive nitrogen intermediate-independent mechanisms and just pa rtially by nutritionally dependent mechanisms. We also suggest that ad ditional mechanisms, still unclear, may be involved, since complete re version was never obtained and since at higher concentrations of IFN-g amma, iron(III) did not induce any significant reversion in the L. pne umophila growth inhibition.