Increased sensitivity to the C-X-C chemokine CINC/gro in a model of chronic inflammation

Objective: The C-C chemokine MCP-1 elicits significant neutrophil emigration in rats with chronic adjuvant-induced inflammation, but not in naive animals. We examined responses to the C-X-C chemokine CINC/gro to determine whether this class of chemokine elicits altered neutrophil responses during chronic inflammation. Methods: CINC/gro was supervised over mesenteric venules of naive rats or animals with chronic adjuvant-induced vasculitis. Antibodies were used to characterize adhesive mechanisms. Results: CINC/gro elicited leukocyte transendothelial migration in adjuvant-immunized rats at 100-fold lower concentrations than required to elicit transmigration in naive animals. In both groups, neutrophils constituted > 95% of the leukocytes recruited by CINC/gro. Using in vitro chemotaxis assays, neutrophils from control and adjuvant-immunized rats responded equally to CINC/gro, suggesting differences in migration were not related to neutrophil phenotype. Differences in adhesion molecule usage were noted in vivo. In control animals, CD18 antibodies blocked CINC/gro-induced neutrophil adhesion and emigration. In adjuvant-immunized animals, an α₄-integrin antibody reduced adhesion and emigration, while a CD18 antibody selectively inhibited emigration. Conclusions: This study demonstrates increased sensitivity to a C-X-C chemokine in a model of chronic inflammation, implicates the α₄-integrin in neutrophil adhesion, and demonstrates that CD18 mediates leukocyte transendothelial migration independent from firm adhesion.