Neutrophils are important cellular mediators in inflammatory bowel disease (IBD). Interleukin (IL)8, a powerful neutrophil chemoattractant, is found in increased quantities in inflamed mucosa, but the cells of origin are uncertain. IL8 gene expression was studied by in situ hybridisation in uninflamed intestinal tissue resected for colon carcinoma (n = 7) and in inflamed colonic tissue resected for IBD (n = 11). Immunohistochemistry was used to assess the phenotype of IL8 expressing macrophages and the production of IL8 protein. Macrophages isolated from intestinal resections and lipopolysaccharide stimulated peripheral blood monocytes treated with 5-aminosalicylic acid, hydrocortisone, and cyclosporin A were examined for IL8 mRNA by northern blotting and IL8 secretion by enzyme linked immunosorbent assay (ELISA). In all cases IL8 mRNA was detected by in situ hybridisation in macrophages and neutrophils adjacent to ulceration in inflamed bowel, but not detected in uninflamed mucosa from carcinoma resections. Recently recruited CD14 positive macrophages were responsible for some of this IL8 expression. IL8 protein was present in the same distribution as mRNA. Epithelial cells in normal and inflamed tissue showed neither mRNA nor protein. IL8 mRNA was expressed significantly more commonly by macrophages from IBD affected than from normal mucosa, and IL8 secretion by IBD but not normal colon macrophages was augmented significantly by lipopolysaccharide treatment. IL8 expression and production by lipopolysaccharide treated blood monocytes was inhibited by the therapeutic agents tested. These results show that neutrophils and recently recruited macrophages are responsible for production of IL8 in IBD, suggesting a mechanism for a continuing cycle of neutrophil attraction. Agents used therapeutically in these diseases may be effective in part by disrupting this cycle.
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