MODULATORY EFFECTS OF THE COLONIC MILIEU ON NEUTROPHIL OXIDATIVE BURST - A POSSIBLE PATHOGENIC MECHANISM OF ULCERATIVE-COLITIS

An important hallmark of ulcerative colitis (UC) is mucosal neutrophil (PMN) infiltration associated with mucosal damage. this suggests that colonic chemoattractants such as bacterial products (e.g., N-formyl-m ethionyl-leucyl-phenylalanine (fMLP), lipopolysaccharide (LPS) reach s ystemic circulation and attract PMNs to the colon. PMNs are then activ ated in the colonic mucosa and release their toxic oxidative metabolit es. However, bacterial products are also present in the systemic circu lation of healthy subjects. Thus we hypothesized that PMNs develop tol erance to colonic factors in the normal state and that this tolerance is absent in UC. We evaluated the PMN respiratory burst in response to stimulation with fMLP, LPS or phorbol 12-myristate 13-acetate (PMA) b y measuring the production of reactive oxygen species (ROS) with both luminol-enhanced chemiluminescence and a cytochrome C reduction assay. PMNs were obtained from control subjects, inactive UC patients, patie nts with UC who had undergone colectomies, and non-UC patients with co lectomies. All three stimuli induced a significant rise in ROS. PMNs f rom non-UC colectomy subjects produced significantly higher ROS than P MNs from control subjects with intact colons in response to both fMLP and EPS, In contrast, PMNs from UC colectomy patients produced levels of ROS similar to those produced by PMNs from UC patients with intact colons in response to fMLP and LPS. Colectomy had no effect on PMA-ind uced ROS production in controls. The observed difference in fMLP-induc ed ROS production in control subjects with intact colons was not due t o fMLP receptor down-regulation because a competition assay performed formed with the fMLP blocker BMLP showed a similar receptor apparent a ffinity in all four groups, We conclude the following: (1) the normal colonic milieu modulates the PMN respiratory burst, resulting In hypor esponsiveness of PMNs to physiologic but not ''pharmacologic'' stimula tion. This effect is not due to receptor down-regulation. (2) UC colon ic milieu does not appear to modulate PMN respiratory burst. This loss of PMN ''tolerance' to colonic factors may have a pathogenic role in the sustained inflammation and tissue damage in UC.