Abstract
Movement of neutrophils to the inflamed lung may be mediated by agonist binding to CXCR2 receptors on their cell surface. Elevated levels of CXCR2 ligands such as CXCL8, CXCL1 and CXCL5 have been detected at elevated levels in the lungs of COPD patients. We investigated the effect of a potent and selective CXCR2 antagonist SB-656933 to inhibit the ability of human neutrophils to express the adhesion molecule CD11b. Human whole blood samples (n=6) were drawn from donors and treated with the CXCR2 selective agonist CXCL1 and neutrophil CD11b expression was measured by FACS using a fluorescent labelled anti-CD11b antibody. CXCL1 elicited a concentration related up-regulation of neutrophil CD11b expression with an EC50 of 12.7 nM ± 2.5. Using a dose of CXCL1 at the EC80, SB-656933 caused a concentration dependent inhibition in neutrophil CD11b expression which was maximal at 10 µM, exhibiting 76.2% ± 4.2 inhibition compared to vehicle-treated controls (p<0.01). Inhibition of CXCL1-induced CD11b expression by SB-656933 gave a characteristic single-site competitive inhibition curve with an IC50 of 1.80 µM ± 0.45. CXCR2 receptor blockade inhibits CD11b adhesion molecule expression on neutrophils and this may be an appropriate therapeutic strategy for inflammatory lung diseases with a neutrophilic component. Analysis of neutrophil CD11b expression could be a useful ex vivo measurement of pharmacokinetic activity for CXCR2 antagonists in clinical studies.