Quantitation and Kinetics of Blood Monocyte Migration to Acute Inflammatory Reactions, and IL-1 Alpha, Tumor Necrosis Factor-alpha, and IFN-gamma

Monocytes migrate from the blood into acute inflammatory reactions, where they differentiate into macrophages, and after 12 to 24 h become the predominant histologic feature of the inflammatory infiltrate. The quantitation of monocyte migration into these reactions has been difficult. This report employs a novel combination of techniques to isolate highly purified monocytes from the blood of rats, and shows that these cells have a normal t1/2 of 26 h and migrate efficiently after i.v. injection into cutaneous acute inflammatory sites. Monocytes labeled with 51Cr accumulated in delayed-type hypersensitivity reactions, and sites injected with killed Escherichia coli, LPS, poly-inosine: cytosine, zymosan-activated serum (ZAS), a source of C5adesArg, and the cytokines IL-1 alpha, TNF-alpha, and IFN-gamma. Both radiolabeled monocytes and neutrophils migrated rapidly to E. coli, LPS, ZAS, IL-1 alpha, and TNF-alpha with a large increase in cell accumulation by 2 h. Neutrophil migration declined rapidly to undetectable levels by 3 to 4 h to all five stimuli, and monocyte migration to ZAS and IL-1 alpha also declined by this time. In contrast, E. coli, LPS, and TNF-alpha caused a sustained migration of monocytes for 5 to 6 h, long after neutrophils had stopped accumulating. Intradermal IFN-gamma did not recruit neutrophils but stimulated a prolonged monocyte migration from 1 to 6 h. Combinations of LPS, TNF-alpha, and IFN-gamma synergistically enhanced the late (> 5 h) but not the early phase of monocyte recruitment. In conclusion, purified monocytes isolated from rat blood can be used to quantify monocyte migration in vivo, and these cells migrate rapidly to cutaneous inflammation and in response to chemotactic factors, IL-1 alpha, TNF-alpha, and IFN-gamma, with initial kinetics similar to those of neutrophils. However, monocyte-selective mechanisms are induced by IFN-gamma and also appear to be involved in prolonged monocyte migration to TNF-alpha, LPS, and E. coli.