Effect of Neutrophils on Nitric Oxide Production from Stimulated Macrophages

During the initial phase of an infection, there is an upregulation of inducible nitric oxide synthase in the macrophages for the production of nitric oxide. This is followed by the recruitment of polymorphonuclear leukocytes (neutrophils) which release arginase. Arginase competes with inducible nitric oxide synthase for a common substrate L arginine. To investigate whether the entry of neutrophils and release of arginase can interfere with nitric oxide production from stimulated mouse macrophages. Neutrophils were isolated from human blood and stimulated with cytodex-3 beads. Cultured macrophages were stimulated with lipopolysaccharide and interferon gamma with or without N (G)-nitro-L-arginine methyl ester or N (omega)-hydroxy-nor-L-arginine. Measurement of NO2 -/NO3 - and urea were done using the spectrophotometer. A significantly higher level of nitric oxide production from stimulated macrophages was observed compared to control. There was a decrease in nitric oxide production when stimulated macrophages were treated with the supernatant from activated neutrophils (p<0.05). Arginase from neutrophils can modulate nitric oxide production from activated macrophages which may affect the course of infection by intracellular bacteria.