Recombinant gamma interferon causes neutrophil migration mediated by the release of a macrophage neutrophil chemotactic factor

A dose-dependent neutrophil migration was observed following the injection of purified (Hu IFN-gamma) or recombinant (rIFN-gamma) human gamma interferon into rat peritoneal cavities. This finding contrasts with their inability to cause chemotaxis in vitro in the Boyden chamber. Neutrophil migration into peritoneal cavities and subcutaneous air pouches induced by both preparations of interferon was abolished by pretreatment of the animals with dexamethasone. IFN-gamma-induced neutrophil migration was enhanced when the macrophage population of the peritoneal cavities was increased by previous injection of thioglycollate and reduced by peritoneal lavage. Macrophage monolayers pretreated either with rIFN-gamma or with lipopolysaccharide from E. coli release into the supernatant a factor that stimulates neutrophil recruitment in animals treated with dexamethasone. Dexamethasone blocked this release but did not affect the neutrophil recruitment induced by this factor. These results suggest that IFN-gamma-induced neutrophil migration in vivo may be mediated by the release from resident macrophages of a neutrophil chemotactic factor and that dexamethasone blockade of neutrophil recruitment by IFN-gamma is due to inhibition of the release of this factor.