Macrophage activation is essential for protection against bacterial pathogens but needs to be regulated to prevent damage to the host. We show a key role for the immune inhibitory receptor CD200R and its ligand CD200 in the context of infection with the Gram-negative human pathogen Neisseria meningitidis. N. meningitidis induced CD200 but downregulated CD200R on macrophages in a manner dependent on Neisserial lipopolysaccharide, Toll-like receptor-4 (TLR-4), and the MyD88 pathway but independent of a known Neisserial receptor, scavenger receptor A (SR-A). Agonists of the pattern-recognition receptors nucleotide oligomerization domain 2 (NOD2) and NACHT-LRR protein 3 (NALP3) also induced CD200. The NF-κB member c-Rel was essential for TLR-, NOD2-, and NALP3-mediated induction of CD200. CD200(-/-) animals showed higher lethality in response to experimental meningococcal septicemia, induced higher levels of proinflammatory cytokines, and recruited increased numbers of activated leukocytes, despite comparable bacterial clearance. Thus CD200 is induced by TLR-, NOD2-, and NALP3-mediated pathways, limiting their function and protecting the host from excessive inflammation.

Bacteria adapt to environmental changes through high-frequency switches in expression of specific phenotypes. Localized hypermutation mediated by simple sequence repeats is an important mechanism of such phase variation (PV) in Neisseria meningitidis. Loss or gain of nucleotides in a poly(C) tract located in the reading frame results in switches in expression of lgtG and determines whether a glucose or a phosphoethanolamine (PEtn) is added at a specific position in the inner core lipopolysaccharide (LPS). Monoclonal antibody (MAb) B5 is bactericidal for N. meningitidis strain 8047 when PEtn is present in the inner core LPS and lgtG is switched "off." Escape from the bactericidal activity of this antibody was examined by subjecting strain 8047 to multiple cycles of growth in the presence of MAb B5 and human serum. Escape variants with alterations in the lgtG repeat tract rapidly accumulated in bacterial populations during selection with this antibody. Strain 8047 was outcompeted in this assay by the 8047 ⌬mutS strain due to the elevated PV rate of this mismatch repair mutant and hence the greater proportion of preexisting phase variants of lgtG in the inoculum. This mutS mutant was also more virulent than strain 8047 during escape from passive protection by MAb B5 in an in vivo infant rat model of bacteremia. These results provide an example of how PV rates can modulate the occurrence and severity of infection and have important implications for understanding the evolution of bacterial fitness in species subject to environmental variations that occur during persistence within and transmission between hosts.

Macrophage Scavenger Receptor A (SR-A) is a major non-opsonic receptor for Neisseria meningitidis on mononuclear phagocytes in vitro, and the surface proteins NMB0278, NMB0667, and NMB1220 have been identified as ligands for SR-A. In this study we ascertain the in vivo role of SR-A in the recognition of N. meningitidis MC58 (serogroup B) in a murine model of meningococcal septicaemia. We infected wild-type and SR-A−/− animals intraperitoneally with N. meningitidis MC58 and monitored their health over a period of 50 hours. We also determined the levels of bacteraemia in the blood and spleen, and measured levels of the pro-inflammatory cytokine interleukin-6 (IL-6). The health of SR-A−/− animals deteriorated more rapidly, and they showed a 33% reduction in survival compared to wild-type animals. SR-A−/− animals consistently exhibited higher levels of bacteraemia and increased levels of IL-6, compared to wild-type animals. Subsequently, we constructed a bacterial mutant (MC58-278-1220) lacking two of the SR-A ligands, NMB0278 and NMB1220. Mutation of NMB0667 proved to be lethal. When mice were infected with the mutant bacteria MC58-278-1220, no significant differences could be observed in the health, survival, bacteraemia, and cytokine production between wild-type and SR-A−/− animals. Overall, mutant bacteria appeared to cause less severe symptoms of septicaemia, and a competitive index assay showed that higher levels of wild-type bacteria were recovered when animals were infected with a 1∶1 ratio of wild-type MC58 and mutant MC58-278-1220 bacteria. These data represent the first report of the protective role of SR-A, a macrophage-restricted, non-opsonic receptor, in meningococcal septicaemia in vivo, and the importance of the recognition of bacterial protein ligands, rather than lipopolysaccharide.

Haemophilus influenzae type b (Hib) is a major cause of invasive bacterial infection in children that can be prevented by a vaccine, but there is still uncertainty about its relative importance in Asia. This study investigated the age-specific prevalence of Hib carriage and its molecular epidemiology in carriage and disease in Nepal. Oropharyngeal swabs were collected from children in Kathmandu, Nepal, from 3 different settings: a hospital outpatient department (OPD), schools, and children's homes. Hib was isolated using Hib antiserum agar plates, and serotyping was performed with latex agglutination. Hib isolates from children with invasive disease were obtained during active microbiological surveillance at Patan Hospital, Kathmandu, Nepal. Genotyping of disease and carriage isolates was undertaken using multilocus sequence typing (MLST). Swabs were taken from 2,195 children, including 1,311 children at an OPD, 647 children attending schools, and 237 children in homes. Overall, Hib was identified in 5.0% (110/2,195; 95% confidence interval [95% CI], 3.9% to 6.4%). MLST was performed on 108 Hib isolates from children carrying Hib isolates and 15 isolates from children with invasive disease. Thirty-one sequence types (STs) were identified, and 20 of these were novel STs. The most common ST isolates were sequence type 6 (ST6) and the novel ST722. There was marked heterogeneity among the STs from children with disease and children carrying Hib. STs identified from invasive infections were those commonly identified in carriage. This study provides evidence of Hib carriage among children in urban Nepal with genetically diverse strains prior to introduction of universal vaccination. The Hib carriage rate in Nepal was similar to the rates observed in other populations with documented high disease rates prior to vaccination, supporting implementation of Hib vaccine in Nepal in 2009.

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Serogroup B meningococci cause the majority of the meningococcal disease burden in developed countries. Production of an effective and safe vaccine for serogroup B organisms has been hampered by the poor immunogenicity of the capsular polysaccharide that defines this group of bacteria. Previous efforts have focused on outer membrane vesicle vaccines, which have been implemented successfully during clonal outbreaks. However, the search for a universal vaccine against endemic polyclonal serogroup B meningococcal disease continues. In this review, we have highlighted recent development of outer membrane vesicle vaccines and progress in the evaluation of recombinant outer membrane protein vaccines.

fThe rate of decay of antibody concentration following serogroup C meningococcal (MenC) polysaccharide-protein conjugate vaccination varies between individuals. This depends partly on vaccination age but may be influenced by human genetics. We studied 721 single nucleotide polymorphisms (SNPs) across 131 candidate genes in a first cohort of 905 Caucasians (11 to 21 years old; mean time after vaccination, 4.9 years) and 30 SNPs across 17 genes in a replication study using 155 children, aged 6 to 12 years (mean time after vaccination, 6.7 years), and 196 infants (1 year old; mean time after vaccination, 8 months). Individuals were classified as responders or nonresponders for total MenC IgG concentration and MenC serum bactericidal antibody (SBA) measurements. Associated genes were examined further for quantitative outcome measures. Fifty-nine SNPs in 37 genes were associated with IgG persistence (adjusted for age at measurement), and 56 SNPs in 36 genes were associated with SBA persistence (adjusted for age at measurement and vaccine used). Three SNPs each within the Toll-like receptor 3 (TLR3) (rs3775291, rs3775292, and rs5743312) and CD44 (rs11033013, rs353644, and rs996076) genes were associated with IgG (adjusted for age at measurement) or SBA (adjusted for age at measurement and vaccine used) persistence in the initial genetic study (P, 0.02 to 0.04). Single SNPs within the TLR3 (rs7657186) (P ‫؍‬ 0.004 [unadjusted]) and CD44 (rs12419062) (P ‫؍‬ 0.01 [unadjusted]) genes were associated with IgG persistence in the replication study. These results suggest that genetic polymorphisms in the TLR3 and CD44 genes are associated with the persistence of the immune response to MenC vaccines 1 to 6 years after vaccination.