Complement factor C3 deposition and serum resistance in isogenic capsule and lipooligosaccharide sialic acid mutants of serogroup B Neisseria meningitidis

Abstract

Serogroup B meningococci express sialic acids on their surfaces as a modification of the lipooligosaccharide (LOS) and as capsular material consisting of ␣2,8-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 ␣-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.

Bacteria under stress by complement and coagulation

“…Neisseria meningitidis expresses an (a2?8)-linked polysaccharide capsule that also contains sialic acids (Kahler et al, 1998). In most serotypes this capsule did not affect C3b deposition (Vogel et al, 1997), but specifically prevented MAC insertion in the OM (Schneider et al, 2007). Recently it was reported that capsule expression in meningococci is enhanced by increased Molecular interplay of complement, coagulation and bacteria temperature, which occurs for instance during inflammation when the bacteria need to interfere with immune killing (Loh et al, 2013).…”

Meningococcal surface fibril (Msf) binds to activated vitronectin and inhibits the terminal complement pathway to increase serum resistance

“…To examine serum survival of acapsulate and capsulate Nm via Msf-acquisition of serum aVn, capsulate MC58 Msf+Dopc and acapsulate H44/DC derivatives were used to represent Nm phenotypes that may be found in the blood and in the nasopharynx. In accordance with other studies on acapsulate serum sensitive Nm (Vogel et al, 1997;Lewis et al, 2010), we used conditions that enabled examination of relative survival properties fully described in Experimental procedures. In 10% PHS supplemented with 16 mg ml -1 aVn (final concentration during incubation), serum survival of Msf-expressing MC58 derivatives increased significantly over DmsfDopc mutant over 1 h period examined ( Fig.…”

A variable genetic island specific for Neisseria gonorrhoeae is involved in providing DNA for natural transformation and is found more often in disseminated infection isolates

“…Gonococci are the causative agent of gonorrhoea, whereas meningococci are the major cause of bacterial meningitis in young adults (Sigurdardottir et al, 1997). Although meningococci normally inhabit the nasal pharynx without causing disease, they express a capsule that allows survival in the bloodstream and provides access to the spinal cord to produce meningitis (Vogel et al, 1997). Colonization by meningococci or commensal Neisseria does not normally elicit an overt inflammatory response (DeVoe, 1982).…”