Molecular Signaling Section, Laboratory of Molecular Immunology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
J Innate Immun. 2013;5(1):2-14. doi: 10.1159/000339572. Epub 2012 Jun 20.
Cultured bacteria release N-formylpeptides, which are potent chemoattractants for phagocytic leukocytes acting at G-protein-coupled receptors FPR1 and FPR2. However, the distribution and immunologic activity of these molecules at mucosal surfaces, where large numbers of bacteria are separated from the immune system by epithelium, remain undefined. To investigate this for the gut, we tested leukocyte responses to cell-free gut luminal contents from C57Bl/6 mice fed a chow diet. Small and large intestine contents were able to compete with labeled N-formylpeptide for binding to FPR1, indicating the presence of FPR1 ligands in the gut lumen. Material from both small and large intestine induced robust calcium flux responses by primary FPR1(+) leukocytes (mouse bone marrow cells and splenocytes and human peripheral blood neutrophils and mononuclear cells), as well as chemotactic responses by both mouse bone marrow cells and human peripheral blood neutrophils. However, unlike defined N-formylpeptides, calcium flux responses induced by gut luminal contents were insensitive both to pertussis toxin treatment of leukocytes and to proteinase K digestion of the samples. Moreover, the gut samples were fully active on neutrophils from mice lacking Fpr1, and the kinetics of the calcium flux response differed markedly for neutrophils and peripheral blood mononuclear cells. The active factor(s) could be dialyzed using a 3.5-kDa pore size membrane. Thus, mouse intestinal lumen contains small, potent and highly efficacious leukocyte chemotactic and activating factors that may be distinct from neutrophils and peripheral blood mononuclear cells and distinct from Fpr1 agonists.
培养的细菌释放 N-甲酰肽，这是一种作用于 G 蛋白偶联受体 FPR1 和 FPR2 的吞噬白细胞的有效趋化因子。然而，在黏膜表面，大量细菌与免疫系统被上皮细胞隔开，这些分子的分布和免疫活性仍未确定。为了研究肠道的这种情况，我们测试了白细胞对来自喂食标准饮食的 C57Bl/6 小鼠的无细胞肠道腔内容物的反应。小肠和大肠内容物能够与标记的 N-甲酰肽竞争结合 FPR1，表明肠道腔中有 FPR1 配体。来自小肠和大肠的材料均可诱导初级 FPR1(+)白细胞（鼠骨髓细胞和脾细胞以及人外周血中性粒细胞和单核细胞）产生强烈的钙流反应，以及鼠骨髓细胞和人外周血中性粒细胞的趋化反应。然而，与定义明确的 N-甲酰肽不同，肠道腔内容物诱导的钙流反应既不受白细胞百日咳毒素处理的影响，也不受样品胰蛋白酶消化的影响。此外，肠道样本在缺乏 Fpr1 的小鼠中性粒细胞上完全有效，钙流反应的动力学在中性粒细胞和外周血单核细胞之间明显不同。活性因子可以使用 3.5 kDa 孔径的膜进行透析。因此，鼠肠腔中含有小而有效且高效的白细胞趋化和激活因子，这些因子可能与中性粒细胞和外周血单核细胞不同，也与 Fpr1 激动剂不同。
