Vogel U, Weinberger A, Frank R, Müller A, Köhl J, Atkinson J P, Frosch M
Institut für Hygiene und Mikrobiologie, Universität Würzburg, Germany.
Infect Immun. 1997 Oct;65(10):4022-9. doi: 10.1128/iai.65.10.4022-4029.1997.
Serogroup B meningococci express sialic acids on their surfaces as a modification of the lipooligosaccharide (LOS) and as capsular material consisting of alpha2,8-linked sialic acid homopolymers. The aim of this study was to elucidate the impact of each sialic acid component on the deposition of complement factor C3 and serum resistance. For this purpose, we used isogenic mutants deficient in capsule expression (a polysialyltransferase mutant) or sialylation of the LOS (a galE mutant) or both (a mutant with a deletion of the cps gene locus). Bactericidal assays using 40% normal human serum (NHS) demonstrated that both the capsule and LOS sialic acid are indispensable for serum resistance. By immunoblotting with monoclonal antibody MAb755 that is specific for the C3 alpha-chain, we were able to demonstrate that C3 from 40% NHS was covalently linked to the surface structures of meningococci as C3b and iC3b, irrespective of the surface sialic acid compounds. However, C3b linkage was more pronounced and occurred on a larger number of target molecules in galE mutants with nonsialylated LOS than in meningococci with wild-type LOS, irrespective of the capsule phenotype. C3b deposition was caused by both the classical pathway (CP) and the alternative pathway of complement activation. Use of 10% NHS revealed that at low serum concentrations, C3 deposition occurred via the CP and was detected primarily on nonsialylated-LOS galE mutants, irrespective of the capsular phenotype. Accordingly, immunoglobulin M (IgM) binding to meningococci from heat-inactivated NHS was demonstrated only in both encapsulated and unencapsulated galE mutants. In contrast, inhibition of IgA binding required both encapsulation and LOS sialylation. We conclude that serum resistance in wild-type serogroup B meningococci can only be partly explained by an alteration of the C3b linkage pattern, which seems to depend primarily on the presence of wild-type LOS, since a serum-resistant phenotype also requires capsule expression.
B群脑膜炎奈瑟菌在其表面表达唾液酸，作为脂寡糖（LOS）的修饰以及由α2,8-连接的唾液酸同聚物组成的荚膜物质。本研究的目的是阐明每种唾液酸成分对补体因子C3沉积和血清抗性的影响。为此，我们使用了缺乏荚膜表达的同基因突变体（多唾液酸转移酶突变体）或LOS唾液酸化的突变体（galE突变体）或两者都缺乏的突变体（cps基因座缺失的突变体）。使用40%正常人血清（NHS）进行的杀菌试验表明，荚膜和LOS唾液酸对于血清抗性都是必不可少的。通过用对C3α链特异的单克隆抗体MAb755进行免疫印迹，我们能够证明来自40%NHS的C3以C3b和iC3b的形式共价连接到脑膜炎奈瑟菌的表面结构上，而与表面唾液酸化合物无关。然而，与具有野生型LOS的脑膜炎奈瑟菌相比，无论荚膜表型如何，C3b连接在LOS未唾液酸化的galE突变体中更明显且发生在更多的靶分子上。C3b沉积是由补体激活的经典途径（CP）和替代途径引起的。使用10%NHS表明，在低血清浓度下，C3沉积通过CP发生，并且主要在LOS未唾液酸化的galE突变体上检测到，而与荚膜表型无关。因此，仅在有荚膜和无荚膜的galE突变体中都证明了免疫球蛋白M（IgM）与热灭活NHS中的脑膜炎奈瑟菌结合。相反，抑制IgA结合需要荚膜化和LOS唾液酸化。我们得出结论，野生型B群脑膜炎奈瑟菌的血清抗性只能部分地通过C3b连接模式的改变来解释，这似乎主要取决于野生型LOS的存在，因为血清抗性表型也需要荚膜表达。
