Macrophages stimulated with lipopolysaccharide release a selective neutrophil recruitment inhibitory factor: an in vivo demonstration.

Intravenous injections of lipopolysaccharide (LPS, 20 micrograms/kg) and of a factor originating from LPS-stimulated macrophage monolayers (Neutrophil Recruitment Inhibitory Factor, NRIF) inhibited neutrophil migration into peritoneal cavities induced by carrageenin in rats for up to 24 h. Mononuclear cell migration induced by thioglycollate was also inhibited by the same treatment with LPS but was not affected by NRIF. We conclude that NRIF specifically blocks neutrophil migration and we suggest that NRIF released into the circulation may constitute an important determinant of septicemia.