Distribution of the interleukin-8 receptors, CXCR1 and CXCR2, in inflamed gut tissue.

There is increasing evidence to suggest that the potent neutrophil chemoattractant interleukin-8 (IL-8) has an important role in the pathogenesis of inflammatory bowel disease. IL-8 mediates its actions via two cell surface receptors, CXCR1 and CXCR2. This paper describes the distribution of these IL-8 receptors in the normal gastrointestinal tract and how this is modified in ulcerative colitis (UC). Paraffin-embedded colonic resection specimens were stained with monoclonal antibodies directed against CXCR1 and CXCR2 in ten cases of total UC, 16 cases of appendicitis, and 11 histologically normal sections. A semiquantitative scale of 0-4 was used to assess the proportion and intensity of positively stained cells within certain defined areas of tissue. A comparative assessment was made of the distribution of various cell populations. Dual immunostaining was used to confirm the phenotype of positively staining cells. In the histologically normal colon, the antibody against CXCR1 stained a subpopulation of macrophages deep to the epithelium and germinal centre lymphocytes. A similar pattern of staining was seen in acute appendicitis, with in addition some positively stained neutrophil polymorphs. In UC, there was up-regulation of CXCR1, with a striking increase in positively stained macrophages throughout the mucosa and of B and T lymphocytes outside the germinal centre areas. There was also intense up-regulation of CXCR1 expression by the luminal epithelium, reflected in the epithelial staining score (mean+/-SE=1.8+/-0.44 for UC cases, vs. 0.23+/-0.16 for controls and 0.25+/-0.14 for acute appendicitis). CXCR2 was only expressed on a small population of lamina propria mononuclear cells and crypt epithelial cells, with no significant differences observed between the groups. These results suggest that IL-8 may, through CXCR1, have a role beyond neutrophil recruitment in mediating the immune response in UC and that this is not merely a consequence of the acute inflammation seen in UC.