RESPIRATORY BURST OF INTESTINAL MACROPHAGES IN INFLAMMATORY BOWEL-DISEASE IS MAINLY CAUSED BY CD14(-DERIVED CELLS()L1(+) MONOCYTE)

Macrophages play a crucial role in intestinal mucosal defence, forming dense subepithelial aggregates, particularly in the colon. One of the ir important bactericidal mechanisms is production of oxygen radicals but this may damage the intestinal epithelium, perhaps as an early ste p in inflammatory bowel disease (IBD). The potential for release of ox ygen radicals from mucosal macrophages in IBD was measured and whether a difference exists between newly arrived (CD14(+)L1(+)) monoctye-lik e cells and resident macrophages (CD14(-)L1(-)), without or with addit ional priming in vitro, was investigated. Lamina propria mononuclear c ells from six patients with IBD and five with a normal intestine were isolated with an ethylenediaminetetra acetic acid/collagenase/dispase technique and cultured for three days. The cells were tested with or w ithout interferon gamma (200 U/ml) priming in the presence or absence of lipopolysaccharide (1 mu g/ml) for the last 48 hours in culture. Sa mples from inflamed IBD mucosa depleted of CD14(+) cells by immunomagn etic beads were compared with their undepleted counterparts and with s amples from virtually normal mucosa from the same patients. The produc tion of oxygen radicals was measured as the amount of reduced cytochro me C 2.5 hours after triggering with phorbol 12-myristate 13-acetate. The oxygen radical production in macrophages from moderately or severe ly inflamed mucosa was reduced by median 69% (range 22%-79%, p<0.027) after depletion of CD14(+) cells, Pathology reaching a level similar t o that found for virtually normal samples from the same IBD patients. Furthermore, this production did not increase significantly in mucosal macrophages from normal reference mucosa and from virtually normal or inflamed IBD mucosa after priming with interferon gamma with or witho ut addition of lipopolysaccharide. Upregulation of a respiratory burst in subepithelial resident macrophages is not a likely pathogenetic st ep in IBD. The increased oxygen radical production shown by macrophage s from IBD lesions can, however, be ascribed to recently extravasated CD14(+)L1(+) monocyte-like cells. Inhibition of extravasation of these reactive cells may form part of a therapeutic approach in the future.