Lee Michael H, Perez-Lopez Araceli, Knodler Leigh A, Nguyen Grace, Walker Gregory T, Behnsen Judith, Silva Steven, Celli Jean, Tamin Melissa A, Liang Michael H, Melchior Karine, Argueta Felix A, Nuccio Sean-Paul, Raffatellu Manuela
Division of Host-Microbe Systems and Therapeutics, Department of Pediatrics, University of California San Diego, La Jolla, California, USA.
Biomedicine Research Unit, Facultad de Estudios Superiores Iztacala, Universidad Nacional Autónoma de México, Tlalnepantla, Estado de México, Mexico.
mBio. 2025 Aug 13;16(8):e0380224. doi: 10.1128/mbio.03802-24. Epub 2025 Jul 14.
Non-typhoidal serovars, such as serovar Typhimurium (STm), are a leading cause of inflammatory diarrhea in otherwise healthy individuals. Among children, the elderly, and immunocompromised individuals, STm can spread to systemic sites and cause potentially lethal bacteremia. Phagocytic cells and the immune complement system are pivotal to preventing the dissemination of STm. PgtE, an STm outer membrane protease, has been previously described to cleave over a dozen mammalian protein substrates , including complement protein C3. However, these activities have mostly been observed with mutant, avirulent strains with a truncated O-antigen that renders bacteria sensitive to complement killing. Here, we report that virulent STm utilizes PgtE to evade complement-mediated killing . The wild-type pathogen increases expression and PgtE proteolytic function within macrophages and in macrophage-like growth conditions, concomitant with physiologic O-antigen truncation in these environments. Furthermore, we found that wild-type STm's resistance to complement-mediated serum and neutrophil killing is PgtE-dependent. We propose that PgtE promotes the systemic spread of STm by acting as a second line of defense against complement when STm escapes from a macrophage.IMPORTANCENon-typhoidal serovars primarily cause gastrointestinal infections but can also lead to bacteremia through mechanisms that are not completely elucidated. Here we show that the outer membrane protease PgtE enables virulent to evade complement-mediated killing , thereby promoting bacteremia. We also demonstrate that expression and PgtE proteolytic function are increased within macrophages and under macrophage-like growth conditions. Upon escaping from macrophages, PgtE protects against complement-mediated killing by serum and neutrophils, promoting the systemic spread of the pathogen. These findings highlight PgtE as a potential therapeutic target for preventing bacteremia.
非伤寒血清型，如鼠伤寒血清型（STm），是健康个体发生炎症性腹泻的主要原因。在儿童、老年人和免疫功能低下的个体中，STm可扩散至全身部位并导致潜在致命的菌血症。吞噬细胞和免疫补体系统对于预防STm的传播至关重要。PgtE是一种STm外膜蛋白酶，此前已被描述可切割十几种哺乳动物蛋白底物，包括补体蛋白C3。然而，这些活性大多是在具有截短O抗原的突变无毒菌株中观察到的，这种截短使细菌对补体杀伤敏感。在此，我们报告有毒力的STm利用PgtE逃避补体介导的杀伤。野生型病原体在巨噬细胞内和类似巨噬细胞的生长条件下增加PgtE的表达和蛋白水解功能，同时在这些环境中伴随着生理性O抗原截短。此外，我们发现野生型STm对补体介导的血清和中性粒细胞杀伤的抗性是PgtE依赖性的。我们提出，当STm从巨噬细胞中逸出时，PgtE作为对抗补体的第二道防线，促进STm的全身扩散。
重要性
非伤寒血清型主要引起胃肠道感染，但也可通过尚未完全阐明的机制导致菌血症。在此我们表明，外膜蛋白酶PgtE使有毒力的菌株能够逃避补体介导的杀伤，从而促进菌血症。我们还证明，在巨噬细胞内和类似巨噬细胞的生长条件下，PgtE的表达和蛋白水解功能会增加。从巨噬细胞逸出后，PgtE可保护病原体免受血清和中性粒细胞介导的补体杀伤，促进病原体的全身扩散。这些发现突出了PgtE作为预防菌血症的潜在治疗靶点。
