Macrophage oxygen-dependent antimicrobial activity. II. The role of oxygen intermediates.

Abstract

The capacity of 3 populations of mouse peritoneal macrophages to generate oxidative metabolites (as judged by extracellular release of H2O2) was compared to their ability to influence the intracellular fate of virulent Toxoplasma gondii. Macrophages from normal mice released little H2O2 and allowed unrestricted multiplication of intracellular toxoplasmas. Cells from chronically infected, immune (IM) mice released 4 times more H2O2 and displayed microbistatic activity. Macrophages from immune-boosted (IB) mice released 25 times more H2O2 than normal cells and rapidly killed the bulk of ingested toxoplasmas within 1 h. When macrophage monolayers were exposed to scavengers of .**GRAPHIC**. H2O2, OH.cntdot. and 1O2, the inhibition of intracellular toxoplasma multiplication by IM macrophages and the killing of toxoplasmas by IB macrophages were reversed. Depriving cells of glucose, which markedly reduced H2O2 release, resulted in similar reversal of IM and IB macrophage anti-Toxoplasma activity. As judged by the effect of the individual oxygen intermediate scavengers, .**GRAPHIC**. and H2O2 appeared to serve as precursors for the key toxic agents which may include OH.cntdot. and 1O2. Providing normal macrophages with an exogenous source of oxidative metabolites generated by xanthine and xanthine oxidase, but not glucose oxidase, resulted in inhibition of intracellular toxoplasma growth. An oxygen-dependent antimicrobial system may be present in mononuclear phagocytes beyond the production of .**GRAPHIC**. and H2O2. Oxygen intermediates may be important in macrophage resistance to the intracellular pathogen T. gondii.