In-vivo blockage of neutrophil migration by LPS is mimicked by a factor released from LPS-stimulated macrophages.

The present study was performed to determine the effect of an intravenous injection of the macrophage-derived neutrophil chemotactic factor (MNCF) (Cunha & Ferreira 1986) on neutrophil migration to rat peritoneal cavities, which were challenged with chemotactic stimuli. Macrophage monolayers stimulated by LPS release a factor (MW greater than 10,000 D) which, when injected intravenously, blocked neutrophil migration in carrageenin-induced peritonitis. This inhibition was dependent on dose and lasted more than 2 h. It was not due to neutropaenia, hypotension or LPS contamination. Neutrophil migration induced by LPS, MNCF, the Gram-negative bacterium Pseudomonas aeruginosa was also blocked by intravenous administration of the factor. Intravenous injection of recombinant interleukin 1 beta or tumour necrosis factor-alpha, present in the samples of the factor, failed to reproduce the described inhibitory effect on neutrophil migration. The release of this factor by LPS-stimulated macrophage monolayers was inhibited by dexamethasone but not by indomethacin. It is suggested that the failure of neutrophils to migrate during septicaemia may be the result of a continuous release of chemotactic factors in the circulation, particularly of the macrophage-derived neutrophil chemotactic factor(s).