Interactions with M Cells and Macrophages as Key Steps in the Pathogenesis of Enterohemorragic <em>Escherichia coli</em> Infections

Enterohemorrhagic Escherichia coli (EHEC) are food-borne pathogens that can cause serious infections ranging from diarrhea to hemorrhagic colitis (HC) and hemolytic-uremic syndrome (HUS). Translocation of Shiga-toxins (Stx) from the gut lumen to underlying tissues is a decisive step in the development of the infection, but the mechanisms involved remain unclear. Many bacterial pathogens target the follicle-associated epithelium, which overlies Peyer's patches (PPs), cross the intestinal barrier through M cells and are captured by mucosal macrophages. Here, translocation across M cells, as well as survival and proliferation of EHEC strains within THP-1 macrophages were investigated using EHEC O157:H7 reference strains, isogenic mutants, and 15 EHEC strains isolated from HC/HUS patients. We showed for the first time that E. coli O157:H7 strains are able to interact in vivo with murine PPs, to translocate ex vivo through murine ileal mucosa with PPs and across an in vitro human M cell model. EHEC strains are also able to survive and to produce Stx in macrophages, which induce cell apoptosis and Stx release. In conclusion, our results suggest that the uptake of EHEC by M cells and underlying macrophages in the PP may be a critical step in Stx translocation and release in vivo. A new model for EHEC infection in humans is proposed that could help in a fuller understanding of EHEC-associated diseases.肠出血性大肠埃希菌（Enterohemorrhagic Escherichia coli, EHEC）是食源性致病菌，可引发从腹泻到出血性结肠炎（hemorrhagic colitis, HC）、溶血性尿毒症综合征（hemolytic-uremic syndrome, HUS）等严重感染。志贺毒素（Shiga-toxins, Stx）从肠腔易位至下层组织是感染发展的决定性步骤，但其相关机制仍不明确。诸多细菌致病菌会靶向覆盖派尔集合淋巴结（Peyer's patches, PPs）的滤泡相关上皮，通过M细胞跨过肠屏障并被黏膜巨噬细胞捕获。本研究利用EHEC O157:H7参考菌株、同基因突变株以及15株从HC/HUS患者体内分离的EHEC菌株，探究了EHEC菌株穿过M细胞的易位过程，以及其在THP-1巨噬细胞内的存活与增殖情况。本研究首次证实，大肠埃希菌O157:H7菌株可在体内与小鼠派尔集合淋巴结相互作用，可离体穿过带有派尔集合淋巴结的小鼠回肠黏膜，也可在体外穿过人源M细胞模型完成易位。EHEC菌株同样能够在巨噬细胞内存活并产生志贺毒素，进而诱导细胞凋亡并释放志贺毒素。综上，本研究结果提示，派尔集合淋巴结内M细胞及下层巨噬细胞对EHEC的摄取，可能是志贺毒素在体内易位与释放的关键步骤。本研究提出了一种全新的人类EHEC感染模型，该模型有助于更全面地解析EHEC相关疾病的致病机制。