The in vivo quantitation and kinetics of rabbit neutrophil leukocyte accumulation in the skin in response to chemotactic agents and Escherichia coli

This report describes the in vivo quantitation of neutrophil accumulation at inflammatory sites in rabbits by employing ⁵¹Cr-labeled autologous rabbit blood neutrophils. These labeled neutrophils circulated with a half-life of 3.2 to 3.8 hr. They were found to localize with great specificity at skin sites injected intradermally with zymosan-activated plasma, synthetic chemotactic peptides (e.g., N-formyl methionyl leucyl phenylalanine), Escherichia coli-derived chemotactic factors, or whole E. coli. Contrary to reports utilizing in vitro assays, under in vivo conditions the synthetic chemotactic peptides caused significantly less neutrophil accumulation than zymosan-activated plasma or E. coli chemotactic factors. No inhibition of neutrophil accumulation by high concentrations of N-formyl methionyl leucyl phenylalanine was observed. Kinetic studies of the accumulation of labeled leukocytes in the skin in response to intradermal injection of formalin-killed E. coli were performed. Nearly all of the leukocytes accumulated during the first 4 hr after E. coli injection with a peak rate of accumulation between 2 and 3 hr. Essentially no additional localization of leukocytes occurred at lesions which were 6, 8, or 24 hr old. These results demonstrate that ⁵¹Cr-labeled rabbit blood neutrophils can be utilized to quantitate the degree of neutrophil accumulation in inflammatory reactions as well as to study the hour by hour kinetics of this accumulation.