CXCR2 regulation of tumor necrosis factor-alpha adherence-dependent peroxide production is significantly diminished after severe injury in human neutrophils

The tripeptide feG inhibits leukocyte adhesion

Background

The tripeptide feG (D-Phe-D-Glu-Gly) is a potent anti-inflammatory peptide that reduces the severity of type I immediate hypersensitivity reactions, and inhibits neutrophil chemotaxis and adhesion to tissues. feG also reduces the expression of β1-integrin on circulating neutrophils, but the counter ligands involved in the anti-adhesive actions of the peptide are not known. In this study the effects of feG on the adhesion of rat peritoneal leukocytes and extravasated neutrophils to several different integrin selective substrates were evaluated.

Results

The adhesion of peritoneal leukocytes and extravasated neutrophils from rats to adhesive proteins coated to 96-well plates was dependent upon magnesium (Mg²⁺) ion, suggestive of integrin-mediated adhesion. feG inhibited leukocyte adhesion, but only if the cells were stimulated with PAF (10^-9M), indicating that feG's actions in vitro require cell activation. In the dose range of 10^-10M to 10^-12M feG inhibited the adhesion of peritoneal leukocytes to fibrinogen and fibronectin, but not IgG, vitronectin or ICAM-1. feG inhibited the binding of extravasated neutrophils to heparin, IgG, fibronectin and CD16 antibody. Antigen-challenge of sensitized rats reduced the adhesion of peritoneal leukocytes to most substrates and abolished the inhibitory effects of feG. However, pretreating the animals with intraperitoneal feG (100 μg/kg) 18 h before collecting the cells from the antigen-challenged animal restored the inhibition of adhesion by in vitro feG of peritoneal leukocytes and extravasated neutrophils to fibronectin.

Conclusion

The modulation of leukocyte adhesion by feG appears to involve actions on αMβ2 integrin, with a possible interaction with the low affinity FcγRIII receptor (CD16). The modulation of cell adhesion by feG is dual in nature. When administered in vivo, feG prevents inflammation-induced reductions in cell adhesion, as well as restoring its inhibitory effect in vitro. The mechanism by which in vivo treatment with feG exerts these effects remains to be elucidated.

Azithromycin Blocks Neutrophil Recruitment inPseudomonasEndobronchial Infection

Macrolides exert their effects on the host by modulation of immune responses. In this study, we assessed the therapeutic efficacy of azithromycin in a murine model of mucoid Pseudomonas aeruginosa endobronchial infection. The clearance of Pseudomonas from the airway of mice treated with the macrolide azithromycin was not different than untreated mice challenged with Pseudomonas beads. However, the azithromycin-treated mice showed a remarkable reduction in lung cellular infiltrate in response to Pseudomonas beads, as compared with untreated mice. This effect was associated with significant decreases in lung levels of tumor necrosis factor-alpha and keratinocyte-derived chemokine in azithromycin-treated mice compared with untreated mice. Furthermore, there was a significant reduction in the response of both mouse and human neutrophils to chemokine-dependent and -independent chemoattractants when studied in vitro. Inhibition of chemotaxis correlated with azithromycin-mediated inhibition of extracellular signal-regulated kinase-1 and -2 activation. This study indicates that the azithromycin treatment in vivo results in significant reduction in airway-specific inflammation, which occurs in part by inhibition of neutrophil recruitment to the lung through reduction in proinflammatory cytokine expression and inhibition of neutrophil migration via the extracellular signal-regulated kinase-1 and -2 signal transduction pathway.