Department of Medical Microbiology and Immunology, School of Medicine, University of California at Davis, One Shields Ave., Davis, CA 95616-8645, USA.
Infect Immun. 2011 Feb;79(2):830-7. doi: 10.1128/IAI.00961-10. Epub 2010 Nov 22.
Capsular polysaccharides are important virulence factors of invasive bacterial pathogens. Here we studied the role of the virulence (Vi) capsular polysaccharide of Salmonella enterica serotype Typhi (S. Typhi) in preventing innate immune recognition by complement. Comparison of capsulated S. Typhi with a noncapsulated mutant (ΔtviBCDE vexABCDE mutant) revealed that the Vi capsule interfered with complement component 3 (C3) deposition. Decreased complement fixation resulted in reduced bacterial binding to complement receptor 3 (CR3) on the surface of murine macrophages in vitro and decreased CR3-dependent clearance of Vi capsulated S. Typhi from the livers and spleens of mice. Opsonization of bacteria with immune serum prior to intraperitoneal infection increased clearance of capsulated S. Typhi from the liver. Our data suggest that the Vi capsule prevents CR3-dependent clearance, which can be overcome in part by a specific antibody response.
荚膜多糖是侵袭性细菌病原体的重要毒力因子。在这里，我们研究了肠伤寒沙门氏菌血清型 Typhi (S. Typhi) 的毒力（Vi）荚膜多糖在防止补体固有免疫识别中的作用。比较有荚膜的 S. Typhi 与无荚膜突变体（ΔtviBCDE vexABCDE 突变体）表明，Vi 荚膜干扰补体成分 3 (C3) 的沉积。补体固定减少导致细菌与鼠巨噬细胞表面补体受体 3 (CR3) 的结合减少，从而降低 Vi 荚膜包裹的 S. Typhi 从肝脏和脾脏中清除的 CR3 依赖性。在腹腔感染前用免疫血清对细菌进行调理，可增加肝脏中荚膜包裹的 S. Typhi 的清除率。我们的数据表明，Vi 荚膜阻止了 CR3 依赖性的清除，而这种清除可以部分被特异性抗体反应所克服。
