Li C K, Seth R, Gray T, Bayston R, Mahida Y R, Wakelin D
Department of Life Science, University of Nottingham, United Kingdom.
Infect Immun. 1998 May;66(5):2200-6. doi: 10.1128/IAI.66.5.2200-2206.1998.
Epithelial cells are the first point of host contact for invasive intestinal pathogens and may initiate mucosal inflammatory responses via production of proinflammatory cytokines and mediators. The aim of the present study was to investigate in vitro the initial invasion of a parasitic nematode (Trichinella spiralis), to measure the early production of specific epithelial cytokines and inflammatory mediators after invasion, and to compare these responses with those to invasive bacteria. Monolayers of human colonic epithelial cell lines (HT29, T84, and Caco-2) were infected by T. spiralis or Listeria monocytogenes. Bile-activated infective larvae of T. spiralis invaded and migrated into the epithelial cell monolayers, leaving trails of dead cells. Transmission electron microscopy studies of damaged cells along the trail showed a progressive increase in size, disruption of cell membranes, loss or dilution of cytoplasmic proteins, and swelling of mitochondria and nuclei. However, no nuclear fragmentation was observed. With reverse transcription-PCR and an enzyme-linked oligonucleotide chemiluminescent assay, mRNA transcripts of interleukin-1beta (IL-1beta), IL-8, and epithelial neutrophil-activating peptide 78 were shown to increase in epithelial cells invaded by T. spiralis or L. monocytogenes, but only L. monocytogenes elicited increased inducible nitric oxide synthase (iNOS) mRNA. No increase in tumor necrosis factor alpha or transforming growth factor beta mRNA was seen after T. spiralis invasion. Increased levels of IL-8 were also released from the basolateral surfaces of infected monolayers as detected by sandwich enzyme-linked immunosorbent assay. Induction and secretion of proinflammatory cytokines in epithelial cells after nematode or bacterial invasion may initiate the acute inflammatory response of the small intestine. The upregulation of iNOS in bacterial infections may contribute to mucosal defense and may also be associated with subsequent cell death, whereas different mechanisms appear to operate after nematode invasion.
上皮细胞是侵袭性肠道病原体与宿主接触的首个位点，可通过产生促炎细胞因子和介质引发黏膜炎症反应。本研究的目的是在体外研究一种寄生线虫（旋毛虫）的初始侵袭情况，测定侵袭后特定上皮细胞因子和炎症介质的早期产生，并将这些反应与侵袭性细菌引起的反应进行比较。用人结肠上皮细胞系（HT29、T84和Caco-2）单层培养物感染旋毛虫或单核细胞增生李斯特菌。胆汁激活的旋毛虫感染性幼虫侵入并迁移到上皮细胞单层中，留下死亡细胞的痕迹。对痕迹沿线受损细胞的透射电子显微镜研究显示，细胞大小逐渐增加，细胞膜破裂，细胞质蛋白丢失或稀释，线粒体和细胞核肿胀。然而，未观察到核碎裂。通过逆转录聚合酶链反应和酶联寡核苷酸化学发光测定法，显示在被旋毛虫或单核细胞增生李斯特菌侵袭的上皮细胞中，白细胞介素-1β（IL-1β）、IL-8和上皮中性粒细胞激活肽78的mRNA转录物增加，但只有单核细胞增生李斯特菌引起诱导型一氧化氮合酶（iNOS）mRNA增加。旋毛虫侵袭后未观察到肿瘤坏死因子α或转化生长因子β mRNA增加。通过夹心酶联免疫吸附测定法检测到，感染单层培养物的基底外侧表面也释放出增加水平的IL-8。线虫或细菌侵袭后上皮细胞中促炎细胞因子的诱导和分泌可能引发小肠的急性炎症反应。细菌感染中iNOS的上调可能有助于黏膜防御，也可能与随后的细胞死亡有关，而线虫侵袭后似乎有不同的机制在起作用。
