Elevated cell-associated levels of interleukin 1β and interleukin 6 in inflamed mucosa of inflammatory bowel disease

The aim of this study was to investigate the involvement of the monocyte-derived cytokines interleukin 1β (IL-1β), interleukin 6 (IL-6) and tumour necrosis factor-α (TNF-α) in idiopathic inflammatory bowel disease. Endoscopic biopsies of normal and inflamed intestinal mucosa were obtained from patients with ulcerative colitis ( n  = 11) and with Crohn's disease ( n  = 10). Intestinal mucosal cells were isolated by collagenase digestion. Cell viability, morphology and CD14 expression were determined. To measure cell-associated cytokine levels, cells were lysed and analysed for IL-1β and TNF-α in specific radioimmunoassays and for IL-6 using a biological assay. Compared with mucosal cells from control patients without inflammatory bowel disease the inflamed intestine in ulcerative colitis and Crohn's disease displayed markedly enhanced levels of IL-1β (median 245 pg 10⁻⁶ cells, range 30–1275) and IL-6 (median 22 U 10⁻⁶ cells, range 1–298). Non-inflamed mucosa in patients with ulcerative colitis and Crohn's disease did not shown elevated levels of IL-1β (median 50 pg 10⁻⁶ cells, range 33–90) or IL-6 (mean below detection limit of assay, i.e. 1 U 10⁻⁶ cells). In contrast, no clear cut difference between inflamed and non-inflamed mucosa could be detected for TNF-α. High tissue levels of IL-6 were associated with a high endoscopic grade of local inflammation. These results suggest that the monocyte-derived cytokines IL-1β and IL-6 are mediators of inflammation in inflammatory bowel disease.