Circulating growth-regulated oncogene alpha contributes to neutrophil priming and interleukin-8-directed mucosal recruitment into chronic lesions of patients with Crohn's disease

Crohn's disease (CD) lesions are characterized by a marked neutrophilic inf iltrate associated with enhanced mucosal IL-8, contrasting with low serum I L-8 levels. The aim of this study was to investigate the effects of circula ting GRO alpha and IL-8 on neutrophil priming and migration. The expression of surface molecules involved in rolling (CD62L, CD15) and firm adhesion ( Mac-1 and LFA-1) to endothelial cells was assessed by flow cytometry, while the chemotactic response of PMN to IL-8 and to fMLP was investigated in a Boyden chamber assay. In addition, IL-8 and GRO alpha levels were determine d by ELISA in plasma samples and in culture supernatants of purified polymo rphonuclear neutrophila (PMN) and peripheral blood mononuclear cells (PBMC) from patients with CD and healthy blood donors. This study revealed an upregulation of CD11b (Mac-1) membrane expression on circulating PMN from patients with CD, as assessed by the mean fluorescenc e intensity which reflects antigen density. Furthermore, an enhanced chemot actic response towards both fMLP and IL-8 of PMN from CD patients was obser ved. Despite often undetectable levels of circulating IL-8, all plasma samp les were positive for GRO alpha, with a significant increase in CD patients when compared to donors. In vitro, equivalent concentrations of GRO alpha were able to increase the IL-8 driven chemotaxis of PMN. In conclusion, blood PMN from patients with CD showed an enhanced capacity to be recruited into inflammed intestinal mucosa, which could be due to an increased expression of CD11b (Mac-1) as well as an increased chemotactic r esponse toward fMLP or IL-8. This priming effect of PMN in CD may partly oc cur through elevated circulating GRO alpha levels.