Of microbes, macrophages and nitric oxide

One of the most prominent functions of nitric oxide (NO) is its participation in antimicrobial and antiviral defense. This paper summarizes the evidence for this function and compiles the infectious agents which are currently thought to be controlled via high out-put generation of NO as it occurs in activated macrophages and other cells expressing the inducible isoform of NO-synthase (iNOS, NOS-2). Several less appreciated forms of interaction between NO and microbes will also be reviewed, including the role of NO as an immunosuppressive or tissue-destructive molecule during the course of infections, the regulation of microbial antioxidant systems by host cell-derived NO, the contribution of NO to parasite stage conversion, the induction or suppression of macrophage iNOS by microbial products, and the existence of endogenous NO synthase pathways in certain bacteria and parasites.