Chemotactic desensitization of neutrophils demonstrates interleukin-8 (IL-8)-dependent and IL-8-independent mechanisms of transmigration through cytokine-activated endothelium.

We have recently shown that an exogenous gradient of interleukin-8 (IL-8) induces the transendothelial migration of neutrophils. Treatment of endothelium with the cytokines IL-1 or tumour necrosis factor (TNF) also causes neutrophil transmigration, and recent evidence suggests that this may be due to endogenous IL-8 produced by the endothelium. We have used specific chemotactic desensitization of neutrophils to investigate the role of IL-8 in transmigration through cytokine-activated endothelium. Preincubation of neutrophils with IL-8 reduced their chemotactic transmigration response to an IL-8 gradient by 81%, demonstrating desensitization. Transmigration in response to cytokine-activated endothelium was inhibited by 104% after IL-8 preincubation, thus tending to support the role of IL-8. However, preincubation with another neutrophil chemotactic factor N-formyl-methionyl-leucyl-phenylalanine (FMLP), which did not affect the IL-8, response, also inhibited transmigration, by 74%. This suggests that FMLP preincubation acts to inhibit a non-IL-8-dependent mechanism of transmigration through cytokine-activated endothelium. Chemotactic factor pretreatment of neutrophils did not reduce their adhesion to activated endothelium, but specifically blocked the transmigration step. We have therefore shown that chemotactic transmigration can be subjected to factor-specific desensitization, and have used this to provide evidence supporting a role for IL-8 in transmigration through cytokine-activated endothelium, as well as suggesting a further IL-8-independent mechanism. These data also provide a mechanism for the observed defect in accumulation of neutrophils at inflammatory sites when chemotactic factors are infused intravenously.