Showing papers by "Ulrich Vogel published in 1997"
TL;DR: It is concluded 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.
Abstract: 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.
120 citations
TL;DR: Analysis of meningococci of serogroups W135 and Y expressing sialic acid heteropolymers revealed that the DNA sequences of the corresponding genetic loci in these serog groups were highly homologous, but differed completely from the siaD genes of serogsroups B and C.
Abstract: The serogroups B, C, W135 and Y of Neisseria meningitidis express chemically and immunologically distinct capsular polysaccharides containing sialic acid. In the case of serogroup B meningococci sialic acid is synthesized by the gene products of a locus termed sia and forms the homopolymers of the capsule. The organization of the genes required for sialic acid synthesis in serogroups B, C, W135 and Y was elucidated by PCR technology. Cloning, sequencing and the functional expression of the polysialyltransferase (PST) genes of serogroups B and C demonstrated that the difference in capsule composition derives from the presence of related, but distinct siaD genes coding for PSTs. Analysis of meningococci of serogroups W135 and Y expressing sialic acid heteropolymers revealed that the DNA sequences of the corresponding genetic loci in these serogroups were highly homologous, but differed completely from the siaD genes of serogroups B and C. This finding suggests that enzymes unrelated to those of serogroups B and C are required for the formation of sialic acid heteropolymers characteristic of the capsules of serogroups W135 and Y.
63 citations
TL;DR: It is demonstrated that lst mutation, in contrast to galE mutation, which results in a truncated LOS, or to siaD mutation, neither had an effect on resistance to normal human serum, nor did it impair the ability of meningococci to spread systemically in the non-immune host.
Abstract: The neisserial α-2,3-sialyltransferase, which is encoded by the lst gene, terminally links sialic acid to the lacto-N-neotetraose residue of neisserial lipooligosaccharide (LOS). We used the recently published nucleotide sequence of the neisserial lst gene to construct an isogenic serogroup B meningococcal lst mutant by insertion of a kanamycin resistance gene. The resulting lst mutant expressed the unsialylated lacto-N-neotetraose structure. Using bactericidal assays and an infant rat model of meningococcal infection, we were able to demonstrate that lst mutation, in contrast to galE mutation, which results in a truncated LOS, or to siaD mutation, which results in loss of the capsule, neither had an effect on resistance to normal human serum, nor did it impair the ability of meningococci to spread systemically in the non-immune host. The lst mutant was serum resistant despite of the fact that the central factor of complement activation, C3b, was deposited on the lst mutant as efficiently as it was on the galE mutant. Thus, the terminal sialic acid residue linked to the wild-type LOS inhibited C3b deposition on the meningocuccus. However, in contrast to the galE mutant, where C3b deposition is promoted by IgM binding, the lst mutant's surface is not a target for IgM molecules. Thus, the lacto-N-neotetraose residue of neisserial LOS alone, without the presence of terminal sialic acid, is sufficient to block IgM epitopes either on the LOS itself, or on other surface molecules. Our data provide further insight into the complex interplay of capsular and LOS sialic acids in serogroup B meningococci with host effector mechanisms, and suggest that LOS sialylation in meningococci is of a less central importance as it is in gonococci.
37 citations
5 citations