Plasma nitrate as an index of immune system activation in animals and man.

The cytotoxic activity of activated macrophages is based upon their formation and release of nitric oxide (NO). In blood NO is rapidly metabolised to nitrate. We analysed plasma nitrate in rats given zymosan, an activator of the immune system, and found 20-fold increases above the basal level. Furthermore, in two human subjects with acute gastro-enteritis plasma nitrate increased from about 30 to 200 microM two days after onset of symptoms. These increased plasma levels of nitrate may reflect macrophage formation of NO. We propose that plasma nitrate may be a useful index for quantitative assessment of cytotoxic activity during immunological challenge.