Rat,mouse andhumanneutrophils stimulated byavariety ofactivating agents produce muchless nitrite thanrodentmacrophages

SUMMARY Theroleofreactive nitrogen intermediates (RNI)intheantimicrobial activities ofneutrophils fromvarious mammalian species isunclear. However, ithasbeenreported thatrodent neutrophils possesstheinducible formofnitric oxidesynthase andthatinflammatory neutrophils fromrats produce potentially antimicrobial levels ofRNI.Inthepresent study, neutrophils fromhumans, ratsandmicewere evaluated forproduction ofnitrite, a stable end-product ofRNI.Human neutrophil preparations (>95%neutrophils) isolated fromperipheral bloodwere stimulated for 2-24hrwithagentsknowntotrigger theCa2+-dependent constitutive nitric oxidesynthase, orto stimulate synthesis oftheinducible nitric oxide synthase. Superoxide dismutase was addedtosome cultures todecrease thelevels ofsuperoxide, a compoundreported toreactwithRNI andyield products other thannitrite. Eventhough thecells were viable andresponsive tostimuli, theydid notproducenitrite concentrations indicative ofantimicrobial potential. Preparations of inflammatory (casein-elicited) mouse neutrophils alsofailed toproduce highconcentrations of nitrite. Inflammatory ratneutrophils (2-5 x 106/ml) produced nitrite concentrations of - 40pMin 24-hr cultures, butplots ofnitrite production versuscell numberforneutrophil andmacrophage preparations indicated thatcontaminating macrophages couldaccountforallthenitrite production intheneutrophil preparations. Thus,neutrophils fromrats, miceandhumansseem comparable intheir inability toproduce highlevels ofnitrite inresponsetoa variety ofstimuli. Thissuggests that inmostcircumstances theconstitutive nitric oxide synthase knowntobepresent inthese cells islimited totheproduction oflowlevels ofnitric oxide forintercellular signalling. In addition, thisraises questions aboutthepresenceor functional status ofinducible nitric oxide synthase inrodent neutrophils.