Keshavarzian A, Haydek J M, Jacyno M, Holmes E W, Harford F
Department of Medicine (Digestive Disease and Nutrition), Loyola University Medical Center, Maywood, Illinois 60153, USA.
J Lab Clin Med. 1997 Aug;130(2):216-25. doi: 10.1016/s0022-2143(97)90099-8.
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-methionyl-leucyl-phenylalanine (fMLP), lipopolysaccharide (LPS)) reach systemic circulation and attract PMNs to the colon. PMNs are then activated in the colonic mucosa and release their toxic oxidative metabolites. However, bacterial products are also present in the systemic circulation of healthy subjects. Thus we hypothesized that PMNs develop tolerance 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) by 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, patients with UC who had undergone colectomies, and non-UC patients with colectomies. All three stimuli induced a significant rise in ROS. PMNs from non-UC colectomy subjects produced significantly higher ROS than PMNs from control subjects with intact colons in response to both fMLP and LPS. 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-induced ROS production in controls. The observed difference in fMLP-induced ROS production in control subjects with intact colons was not due to fMLP receptor down-regulation because a competition assay performed with the fMLP blocker BMLP showed a similar receptor apparent affinity in all four groups. We conclude the following: (1) the normal colonic milieu modulates the PMN respiratory burst, resulting in hyporesponsiveness of PMNs to "physiologic" but not "pharmacologic" stimulation. This effect is not due to receptor down-regulation. (2) UC colonic 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.
溃疡性结肠炎（UC）的一个重要标志是与黏膜损伤相关的黏膜中性粒细胞（PMN）浸润。这表明结肠趋化因子，如细菌产物（如N-甲酰甲硫氨酰亮氨酰苯丙氨酸（fMLP）、脂多糖（LPS））进入体循环并吸引PMN至结肠。然后PMN在结肠黏膜中被激活并释放其有毒的氧化代谢产物。然而，细菌产物在健康受试者的体循环中也存在。因此我们推测，PMN在正常状态下对结肠因子产生耐受，而在UC中这种耐受缺失。我们通过鲁米诺增强化学发光法和细胞色素C还原试验测量活性氧（ROS）的产生，评估了PMN对fMLP、LPS或佛波醇12-肉豆蔻酸酯13-乙酸酯（PMA）刺激的呼吸爆发。PMN取自对照受试者、非活动期UC患者、接受结肠切除术的UC患者以及接受结肠切除术的非UC患者。所有三种刺激均导致ROS显著升高。非UC结肠切除受试者的PMN在对fMLP和LPS的反应中产生的ROS显著高于结肠完整的对照受试者的PMN。相比之下，UC结肠切除患者的PMN产生的ROS水平与结肠完整的UC患者的PMN对fMLP和LPS的反应中产生的水平相似。结肠切除术对对照受试者中PMA诱导的ROS产生没有影响。在结肠完整的对照受试者中观察到的fMLP诱导的ROS产生差异并非由于fMLP受体下调，因为用fMLP阻滞剂BMLP进行的竞争试验显示所有四组中的受体表观亲和力相似。我们得出以下结论：（1）正常结肠环境调节PMN呼吸爆发，导致PMN对“生理性”而非“药理学性”刺激反应低下。这种效应不是由于受体下调。（2）UC结肠环境似乎不调节PMN呼吸爆发。PMN对结肠因子“耐受”的丧失可能在UC的持续炎症和组织损伤中起致病作用。
