Rat, mouse and human neutrophils stimulated by a variety of activating agents produce much less nitrite than rodent macrophages

Abstract

The role of reactive nitrogen intermediates (RNI) in the antimicrobial activities of neutrophils from various mammalian species is unclear. However, it has been reported that rodent neutrophils possess the inducible form of nitric oxide synthase and that inflammatory neutrophils from rats produce potentially antimicrobial levels of RNI. In the present study, neutrophils from humans, rats and mice were evaluated for production of nitrite, a stable end-product of RNI. Human neutrophil preparations (> 95% neutrophils) isolated from peripheral blood were stimulated for 2-24 hr with agents known to trigger the Ca(2+)-dependent constitutive nitric oxide synthase, or to stimulate synthesis of the inducible nitric oxide synthase. Superoxide dismutase was added to some cultures to decrease the levels of superoxide, a compound reported to react with RNI and yield products other than nitrite. Even though the cells were viable and responsive to stimuli, they did not produce nitrite concentrations indicative of antimicrobial potential. Preparations of inflammatory (casein-elicited) mouse neutrophils also failed to produce high concentrations of nitrite. Inflammatory rat neutrophils (2.5 x 10(6)/ml) produced nitrite concentrations of approximately 40 microM in 24-hr cultures, but plots of nitrite production versus cell number for neutrophil and macrophage preparations indicated that contaminating macrophages could account for all the nitrite production in the neutrophil preparations. Thus, neutrophils from rats, mice and humans seem comparable in their inability to produce high levels of nitrite in response to a variety of stimuli. This suggests that in most circumstances the constitutive nitric oxide synthase known to be present in these cells is limited to the production of low levels of nitric oxide for intercellular signalling. In addition, this raises questions about the presence or functional status of inducible nitric oxide synthase in rodent neutrophils.