MACROPHAGE SUBPOPULATIONS AND INTERLEUKIN-1-BETA TISSUE-LEVELS IN PELVIC ILEAL POUCHES

Objective: To characterize macrophage subpopulations and to determine interleukin 1beta mucosal levels in pelvic ileal pouches and without pouchitis. Design and methods: The study included 30 patients who had undergone proctocolectomy with ileal pouch anastomosis; pouchitis was present in 10. Macrophage subpopulations were characterized immunohistochemically in pouch biopsy specimens using a panel of monoclonal antibodies. Concentration of interleukin-1beta was determined by a solid phase enzyme-linked immunosorbent assay in tissue homogenates of mucosal biopsy specimens. Normal ileal mucosa was used as a control. Results: Studies in pouchitis tissue showed a significant increase in the number of macrophages stained with the monoclonal antibody RFD9 (epithelioid cells and tingible body macrophages; median 8.7%, range 4.2-12.7%) compared with pouches without pouchitis (median 0.8%, range 0-2.4%) and normal ileal mucosa (median 0.4%, range 0-1.4%; P<0.001). There were no significant differences between the three groups in the proportion of positive cells for the other macrophage markers (RFD1, dendritic cells; RFD7, mature macrophages). Concentrations of interleukin-1beta were significantly greater in pouchitis specimens compared with either those from pouches without pouchitis or normal ileal mucosa (P<0.001). In pouchitis, tissue levels of interleukin-1beta significantly correlated with the percentage of RFD9-positive macrophages (P<0.01). Conclusions: The significance of the increase in RFD9-positive macrophage levels is unknown. This histochemical pattern also occurs in inflammatory bowel disease and cannot be attributed to non-specific mucosal damage. Its presence, together with the significant increase in interleukin-1beta tissue levels, may suggest that there is a similar pathogenic mechanism for pouchitis and ulcerative colitis.