Seroprevalence of bactericidal and anti-outer membrane vesicle antibodies to Neisseria meningitidis group B in England

Hybrid response to SARS-CoV-2 and Neisseria meningitidis C after an OMV-adjuvanted immunization in mice and their offspring

COVID-19, caused by SARS-CoV-2, and meningococcal disease, caused by Neisseria meningitidis, are relevant infectious diseases, preventable through vaccination. Outer membrane vesicles (OMVs), released from Gram-negative bacteria, such as N. meningitidis, present adjuvant characteristics and may confer protection against meningococcal disease. Here, we evaluated in mice the humoral and cellular immune response to different doses of receptor binding domain (RBD) of SARS-CoV-2 adjuvanted by N. meningitidis C:2a:P1.5 OMVs and aluminum hydroxide, as a combined preparation for these pathogens. The immunization induced IgG antibodies of high avidity for RBD and OMVs, besides IgG that recognized the Omicron BA.2 variant of SARS-CoV-2 with intermediary avidity. Cellular immunity showed IFN-γ and IL-4 secretion in response to RBD and OMV stimuli, demonstrating immunologic memory and a mixed Th1/Th2 response. Offspring presented transferred IgG of similar levels and avidity as their mothers. Humoral immunity did not point to the superiority of any RBD dose, but the group immunized with a lower antigenic dose (0.5 μg) had the better cellular response. Overall, OMVs enhanced RBD immunogenicity and conferred an immune response directed to N. meningitidis too.

Convergent impact of vaccination and antibiotic pressures on pneumococcal populations

Streptococcus pneumoniae is a remarkably adaptable and successful human pathogen, playing dual roles of both asymptomatic carriage in the nasopharynx and invasive disease including pneumonia, bacteremia, and meningitis. Efficacious vaccines and effective antibiotic therapies are critical to mitigating morbidity and mortality. However, clinical interventions can be rapidly circumvented by the pneumococcus by its inherent proclivity for genetic exchange. This leads to an underappreciated interplay between vaccine and antibiotic pressures on pneumococcal populations. Circulating populations have undergone dramatic shifts due to the introduction of capsule-based vaccines of increasing valency imparting strong selective pressures. These alterations in population structure have concurrent consequences on the frequency of antibiotic resistance profiles in the population. This review will discuss the interactions of these two selective forces. Understanding and forecasting the drivers of antibiotic resistance and capsule switching are of critical importance for public health, particularly for such a genetically promiscuous pathogen as S. pneumoniae.

A recombinant commensal bacteria elicits heterologous antigen-specific immune responses during pharyngeal carriage

The human nasopharynx contains a stable microbial ecosystem of commensal and potentially pathogenic bacteria, which can elicit protective primary and secondary immune responses. Experimental intranasal infection of human adults with the commensal Neisseria lactamica produced safe, sustained pharyngeal colonization. This has potential utility as a vehicle for sustained release of antigen to the human mucosa, but commensals in general are thought to be immunologically tolerated. Here, we show that engineered N. lactamica, chromosomally transformed to express a heterologous vaccine antigen, safely induces systemic, antigen-specific immune responses during carriage in humans. When the N. lactamica expressing the meningococcal antigen Neisseria Adhesin A (NadA) was inoculated intranasally into human volunteers, all colonized participants carried the bacteria asymptomatically for at least 28 days, with most (86%) still carrying the bacteria at 90 days. Compared to an otherwise isogenic but phenotypically wild-type strain, colonization with NadA-expressing N. lactamica generated NadA-specific immunoglobulin G (IgG)- and IgA-secreting plasma cells within 14 days of colonization and NadA-specific IgG memory B cells within 28 days of colonization. NadA-specific IgG memory B cells were detected in peripheral blood of colonized participants for at least 90 days. Over the same period, there was seroconversion against NadA and generation of serum bactericidal antibody activity against a NadA-expressing meningococcus. The controlled infection was safe, and there was no transmission to adult bedroom sharers during the 90-day period. Genetically modified N. lactamica could therefore be used to generate beneficial immune responses to heterologous antigens during sustained pharyngeal carriage.

Commensal Neisseria Kill Neisseria gonorrhoeae through a DNA-Dependent Mechanism

The mucosa is colonized with commensal Neisseria. Some of these niches are sites of infection for the STD pathogen Neisseria gonorrhoeae (Ngo). Given the antagonistic behavior of commensal bacteria toward their pathogenic relatives, we hypothesized that commensal Neisseria may negatively affect Ngo colonization. Here, we report that commensal species of Neisseria kill Ngo through a mechanism based on genetic competence and DNA methylation state. Specifically, commensal-triggered killing occurs when the pathogen takes up commensal DNA containing a methylation pattern that it does not recognize. Indeed, any DNA will kill Ngo if it can enter the cell, is differentially methylated, and has homology to the pathogen genome. Consistent with these findings, commensal Neisseria elongata accelerates Ngo clearance from the mouse in a DNA-uptake-dependent manner. Collectively, we propose that commensal Neisseria antagonizes Ngo infection through a DNA-mediated mechanism and that DNA is a potential microbicide against this highly drug-resistant pathogen.

Protection Against Invasive Infections in Children Caused by Encapsulated Bacteria

The encapsulated bacteria Streptococcus pneumoniae, Neisseria meningitis, Haemophilus influenzae, and Streptococcus agalactiae (Group B Streptococcus) have been responsible for the majority of severe infections in children for decades, specifically bacteremia and meningitis. Isolates which cause invasive disease are usually surrounded by a polysaccharide capsule, which is a major virulence factor and the key antigen in protective protein-polysaccharide conjugate vaccines. Protection against these bacteria is largely mediated via polysaccharide-specific antibody and complement, although the contribution of these and other components, and the precise mechanisms, vary between species and include opsonophagocytosis and complement-dependent bacteriolysis. Further studies are required to more precisely elucidate mechanisms of protection against non-type b H. influenzae and Group B Streptococcus.

Evidence for Rise in Meningococcal Serogroup C Bactericidal Antibody Titers in the Absence of Booster Vaccination in Previously Vaccinated Children

BACKGROUND

The introduction of meningococcal serogroup C (MenC) conjugate vaccines in the United Kingdom and Australia led to an impressive decline in the incidence of invasive disease. This study examined bactericidal antibody titers over time in the UK and Australian children who received a MenC conjugate vaccine in early childhood to test the hypothesis that ongoing boosting of immunity in the absence of further doses of vaccine in some children may contribute to ongoing protection from disease.

METHODS

Serum bactericidal assay using rabbit complement (rSBA) titers at each follow-up visit were compared with all preceding visits to identify any ≥4-fold rise in titers. The proportion of children with a ≥4-fold rise in rSBA titers in paired sera at any visit-to-visit comparison was calculated.

RESULTS

Of 392 children with at least one set of paired sera in the Australian cohort, 72 (18.4%) had a ≥4-fold increase in rSBA titers at least one year after vaccination, including six children (1.5%) who showed evidence of boosting twice. Of 234 children with at least one set of paired sera in the UK cohort, 39 (16.7%) had a ≥4-fold rise in rSBA titers at least one year after vaccination including 2 children (0.9%) with evidence of boosting twice.

CONCLUSIONS

A substantial minority of children immunized with MenC conjugate vaccine in early childhood had a rise in bactericidal antibody titers in the years after immunization in the absence of booster vaccination. This occurs most commonly at around 6-7 years of age corresponding to school entry and greater social mixing and might indicate exposure to MenC carriage.

Impact of meningococcal group B OMV vaccines, beyond their brief

Meningococcal group B outer membrane vesicle vaccines have been used widely in Cuba, New Zealand, and Brazil. They are immunogenic and initially assessed largely by their ability to induce serum bactericidal activity. Measures of efficacy indicate good protection against homologous strains in older children and adults. Effectiveness appears broader than predicted by immunogenicity and efficacy studies. The recent discovery that meningococcal group B OMVs may protect against the related Neisseria species N.gonorrhoeae suggests more to these interesting antigen collections than meets the eye. Currently there are two OMV-containing group B vaccines available, the new recombinant protein-based Bexsero® developed by Novartis and VA-MENGOC-BC® developed by the Finlay institute in Cuba. Also, a third group B vaccine based on two recombinant factor H binding proteins (Trumenba®, Pfizer), has recently been licenced but it does not include OMV. This commentary explores the population impact that group B OMV vaccines have had on meningococcal and gonorrhoea diseases. Given the heterologous effect against diverse strains of the meningococcus observed in older children and adults, and recent evidence to suggest moderate protection against gonorrhoea, there may be a role for these vaccines in programmes targeting adolescents and groups high at risk for both meningococcal disease and gonorrhoea.

Investigation of correlates of protection against pharyngeal carriage of Neisseria meningitidis genogroups W and Y in the African meningitis belt

BACKGROUND

Serum bactericidal antibody titres that correlate with protection against invasive meningococcal disease have been characterised. However, titres that are associated with protection against acquisition of pharyngeal carriage of Neisseria meningitidis are not known.

METHODS

Sera were obtained from the members of a household in seven countries of the African meningitis belt in which a pharyngeal carrier of N. meningitidis had been identified during a cross-sectional survey. Serum bactericidal antibody titres at baseline were compared between individuals in the household of the carrier who became a carrier of a meningococcus of the same genogroup during six months of subsequent follow-up and household members who did not become a carrier of a meningococcus of this genogroup during this period.

RESULTS

Serum bacterial antibody titres were significantly higher in carriers of a serogroup W or Y meningococcus at the time of recruitment than in those who were not a carrier of N. meningitidis of the same genogroup. Serum bactericidal antibody titres to a strain of N. meningitis of the same genogroup as the index cases were no different in individuals who acquired carriage with a meningococcus of the same genogroup as the index case than in those who did not become a carrier during six months of follow-up.

CONCLUSION

Serum bacterial antibody titres to N. meningitidis of genogroup W or Y in the range of those acquired by natural exposure to meningococci of these genogroups, or with cross-reactive bacteria, are not associated with protection against acquisition of carriage with meningococci of either of these genogroups.

Seroprevalence of bactericidal antibodies against serogroup B and C Meningococci in a University Hospital

Meningococcus serogroup B (MenB), clonal complex 32 (cc 32), was the Brazilian epidemic strain of meningococcal disease (MD) in the 1990's. Currently, meningococcus serogroup C (MenC), cc 103, is responsible for most of the cases of the disease in Brazil. The aim of this study was to investigate the seroprevalence of bactericidal antibody (SBA) against representative epidemic strains of MenC, (N753/00 strain, C:23:P1.22,14-6, cc103) and MenB, (Cu385/83 strain, B:4,7:P1.15,19, cc32) in students and employees of a university hospital in the State of Rio Grande do Sul (RS, Brazil). A second MenC strain (N79/96, C:2b:P1.5-2,10, cc 8) was used as a prototype strain of Rio de Janeiro's outbreak that occurred in the 1990's. Our previous study showed a 9% rate of asymptomatic carriers in these same individuals. A second goal was to compare the SBA prevalence in meningococcal carriers and non-carriers. Fifty-nine percent of the studied population showed protective levels of SBA titers (log2≥2) against at least one of the three strains. About 40% of the individuals had protective levels of SBA against N753/00 and Cu385/83 strains. Nonetheless, only 22% of the individuals showed protective levels against N79/96 strain. Significantly higher antibody levels were seen in carriers compared to non-carriers (P≤0.009). This study showed that, similar to other States in Brazil, a MenC (23:P1.22,14-6, cc103) strain with epidemic potential is circulating in this hospital. Close control by the Epidemiological Surveillance Agency of RS of the number of cases of MD caused by MenC strains in the State is recommended to prevent a new disease outbreak.

Seroprevalence of Antibody-Mediated, Complement-Dependent Opsonophagocytic Activity against Neisseria meningitidis Serogroup B in England

The correlate of protection for the licensure of meningococcal vaccines is serum bactericidal activity. However, evidence indicates that a complex situation and other mechanisms, such as antibody-mediated, complement-dependent opsonophagocytosis (OP), may play a role in protection and should be investigated in order to understand immunity to this disease. In this study, a high-throughput flow cytometric opsonophagocytic assay (OPA) was optimized. The assay measures the presence of killed fluorescently labeled Neisseria meningitidis within human granulocytes (differentiated HL60 cells) by flow cytometry, using IgG-depleted pooled human plasma as an exogenous source of complement. This method was found to be reliable and correlated with the results of an opsonophagocytic killing assay. The OPA was used to measure OP activity in 1,878 serum samples from individuals ranging from 0 to 99 years of age against N. meningitidis strain NZ98/254 (B:4:P1.7-2,4). The levels of OP activity in individual serum samples varied greatly. OP activity showed an initial peak in the 6- to 12-month age group corresponding to a peak in disease incidence. The OP activity dropped in childhood until the late teenage years, although there was still a higher percentage of individuals with OP activity than with protective bactericidal antibody titers. OP activity reached a peak in the 30- to 39-year age group and then declined. This later peak in OP activity did not coincide with the young adults in whom peak serum bactericidal activity and disease incidence occurred. The demonstration of OP activity when disease incidence is low and when protective bactericidal antibody titers are not detected may indicate a role for OP in protection from meningococcal disease in these age groups.

Oropharyngeal Colonization With Neisseria lactamica, Other Nonpathogenic Neisseria Species and Moraxella catarrhalis Among Young Healthy Children in Ahvaz, Iran

BACKGROUND

Neisseria lactamica as one of the main commensal in oropharynx during the childhood is related to the induction of a natural immunity against meningococcal meningitis. Also Moraxella catarrhalis in oropharynx of children is a predisposing factor for otitis media infection.

OBJECTIVES

The current study aimed to investigate the frequency of the N. lactamica, other nonpathogenic Neisseria spp. and M. catarrhalis in the oropharynx of young healthy children in Ahvaz, Iran by the two phenotypic tests and Polymerase Chain Reaction (PCR).

MATERIALS AND METHODS

A total of 192 oropharyngeal swab samples of the young healthy children were studied during four months. Swabs were plated onto enriched selective media and non-selective media. Gram-negative and oxidase-positive diplococci were identified by several conventional biochemical tests. The PCR and sequencing were used to confirm the accuracy of laboratory diagnosis to identify N. lactamica and M. catarrhalis.

RESULTS

Among 192 young healthy children with the mean age of 5.93 ± 2.5903 years, authors identified: N. lactamica (21.9%) in the age group of one to nine years; N. mucosa (6.3%); N. sicca (7.8%); N. cinerea (1.6%); N. subflava (biovar subflava) (4.2%); N. subflava (biovar perflava) (28.1%); N. subflava (biovar flava) (7.3%) and M. catarrhalis (42.7%).

CONCLUSIONS

The young healthy children screening by colonization of N. lactamica and other nonpathogenic Neisseria spp. in oropharynx was the first report in Ahvaz, Iran. The study results demonstrated the high frequency of colonization of M. catarrhalis in the studied young healthy children other than Neisseria spp.

Neisserial Molecular Adaptations to the Nasopharyngeal Niche

The exclusive reservoir of the genus Neisseria is the human. Of the broad range of species that comprise the Neisseria, only two are frequently pathogenic, and only one of those is a resident of the nasopharynx. Although Neisseria meningitidis can cause severe disease if it invades the bloodstream, the vast majority of interactions between humans and Neisseria are benign, with the bacteria inhabiting its mucosal niche as a non-invasive commensal. Understandably, with the exception of Neisseria gonorrhoeae, which preferentially colonises the urogenital tract, the neisseriae are extremely well adapted to survival in the human nasopharynx, their sole biological niche. The purpose of this review is to provide an overview of the molecular mechanisms evolved by Neisseria to facilitate colonisation and survival within the nasopharynx, focussing on N. meningitidis. The organism has adapted to survive in aerosolised transmission and to attach to mucosal surfaces. It then has to replicate in a nutrition-poor environment and resist immune and competitive pressure within a polymicrobial complex. Temperature and relative gas concentrations (nitric oxide and oxygen) are likely to be potent initial signals of arrival within the nasopharyngeal environment, and this review will focus on how N. meningitidis responds to these to increase the likelihood of its survival.

Meningococcal disease and the complement system

Despite considerable advances in the understanding of the pathogenesis of meningococcal disease, this infection remains a major cause of morbidity and mortality globally. The role of the complement system in innate immune defenses against invasive meningococcal disease is well established. Individuals deficient in components of the alternative and terminal complement pathways are highly predisposed to invasive, often recurrent meningococcal infections. Genome-wide analysis studies also point to a central role for complement in disease pathogenesis. Here we review the pathophysiologic events pertinent to the complement system that accompany meningococcal sepsis in humans. Meningococci use several often redundant mechanisms to evade killing by human complement. Capsular polysaccharide and lipooligosaccharide glycan composition play critical roles in complement evasion. Some of the newly described protein vaccine antigens interact with complement components and have sparked considerable research interest.

Development of a large scale human complement source for use in bacterial immunoassays

The serum bactericidal assay is the correlate of protection for meningococcal disease but the use and comparison of functional immunological assays for the assessment of meningococcal vaccines is complicated by the sourcing of human complement. This is due to high levels of immunity in the population acquired through natural meningococcal carriage and means that many individuals must be screened to find donors with suitably low bactericidal titres against the target strain. The use of different donors for each meningococcal strain means that comparisons of assay responses between strains and between laboratories is difficult. We have developed a method for IgG-depletion of 300 ml batches of pooled human lepirudin-derived plasma using Protein G sepharose affinity chromatography that retains complement activity. However, IgG-depletion also removed C1q. This was also eluted from the affinity matrix, concentrated and added to the complement source. The final complement source retained mean alternative pathway activity of 96.8% and total haemolytic activity of 84.2% in four batches. Complement components C3, C5, properdin and factor H were retained following the process and the IgG-depleted complement was shown to be suitable for use in antibody-mediated complement deposition and serum bactericidal activity assays against serogroup B meningococci. The generation of large IgG-depleted batches of pooled human plasma allows for the comparison of immunological responses to diverse meningococcal strain panels in large clinical trials.

Seroprevalence of bactericidal, specific IgG antibodies and incidence of meningitis due to group A Neisseria meningitidis by age in Burkina Faso 2008

Background

We investigated serological correlates of protection against Neisseria meningitidis serogroup A (NmA) in Burkina Faso before the introduction of NmA conjugate vaccine.

Methodology/Principal Findings

We collected blood from a representative sample (N = 1022) of Bobo-Dioulasso residents. Sera were evaluated for serum bactericidal antibody (SBA) activity against NmA strains of immunotype L11 (F8238) and L10 (3125) and NmA-specific IgG. Seroprevalence was compared to the age-specific NmA meningitis incidence in Bobo-Dioulasso during March 2007–February 2008. Meningococcal carriage was evaluated in a subset (N = 538). Geometric mean titres (GMT)/concentrations (GMC) of SBA and NmA-specific IgG increased with age, peaking around age 20 years. Overall, 70% of our sample had NmA-specific IgG ≥2 ug/mL. Meningitis incidence was highest in those aged <6 months and 5–19 years. No NmA carriers were found. Compared to the reference strain SBA, GMTs were higher against a locally isolated strain and around 40-fold lower against Dutch strain 3125.

Conclusions/Significance

This study provides estimates of natural immunity to NmA, according to a variety of antibody measures, which will be helpful in ascertaining antibody persistence after MenAfriVac™ introduction. Age-specific seroprevalence of reference strain SBA titres most likely reflects exposure to meningococci and consecutive reactive immunity. We could not define any serological correlate of protection.

Evolution of immune response against Neisseria meningitidis B:14:P1.7,16 before and after the outer membrane vesicle vaccine MenBvac

A meningococcal B:14:P1.7,16 outbreak in Normandy (France) was recently controlled using MenBvac, an outer membrane vesicle vaccine previously designed against the B:15:P1.7,16 strain. The further emergence of a new B:14:P1.7,16 outbreak in another district in Normandy led us to explore immunity against B:14:P1.7,16 before and after the MenBvac campaign using a 2+1 (day 0, week 6, month 8) schedule. Children (1-5 years) were sampled before, during and up to one year after vaccination. Serum bactericidal activity against B:14:P1.7,16 was titrated using human complement (hSBA) and immune response was defined by hSBA titer ≥4 as a surrogate for protection. The percentage of hSBA titer ≥4 was 10.8% before vaccination, raised to 84.1% 6 weeks after the completion of the schedule, but declined to 39.7% one year later. This level is lower than the targeted 60% level and suggests only short-term persistence of response against B:14:P1.7,16 using this schedule.

Seroprevalence of serum bactericidal antibodies against group W135 and Y meningococci in England in 2009

Serological surveillance has been used in the United Kingdom to inform vaccine policy for several infections, including those with group C meningococci. Meningococcal conjugate vaccines, containing capsular groups A, W135, and Y in addition to C, are now available, but their use in the United Kingdom is restricted to at-risk groups and travelers to areas of endemicity. The aim of this study was to establish a baseline for natural immunity for groups W135 and Y. Serum samples collected in 2009 from individuals of all ages were obtained from the Health Protection Agency Seroepidemiology Unit, which collects residual sera from participating laboratories across the country. Serum bactericidal antibody (SBA) activity against two reference strains, representing groups Y (strain M03 241125) and W135 (strain M01 240070), was determined with 1,191 sera using a standardized complement-mediated SBA assay, with complement derived from baby rabbits (rSBA). The age-specific geometric mean titers (GMTs) and percentages of individuals with rSBA titers of ≥ 8 were calculated, together with 95% confidence intervals (CI). Overall, 18.4% and 19.6% had rSBA titers of ≥ 8 for groups W135 and Y, respectively. Antibody prevalence varied by age. In general, rSBA titers were low for younger children, with serum samples from 7% and 13% of children under 5 years achieving titers of ≥ 8 against groups W135 and Y, respectively. GMTs peaked for 20- to 24-year-olds for group W135 (GMT, 7.1; 95% CI, 4.7, 10.9) and for 30- to 44-year-olds for group Y (GMT, 8.6; 95% CI, 5.9, 12.7). Unlike seroprevalence against group B meningococci, there was not an obvious peak in SBA titers in samples from teenagers. Natural immunity against group W135 and Y meningococci in England appears to be low.

Infections of people with complement deficiencies and patients who have undergone splenectomy

The complement system comprises several fluid-phase and membrane-associated proteins. Under physiological conditions, activation of the fluid-phase components of complement is maintained under tight control and complement activation occurs primarily on surfaces recognized as "nonself" in an attempt to minimize damage to bystander host cells. Membrane complement components act to limit complement activation on host cells or to facilitate uptake of antigens or microbes "tagged" with complement fragments. While this review focuses on the role of complement in infectious diseases, work over the past couple of decades has defined several important functions of complement distinct from that of combating infections. Activation of complement in the fluid phase can occur through the classical, lectin, or alternative pathway. Deficiencies of components of the classical pathway lead to the development of autoimmune disorders and predispose individuals to recurrent respiratory infections and infections caused by encapsulated organisms, including Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae. While no individual with complete mannan-binding lectin (MBL) deficiency has been identified, low MBL levels have been linked to predisposition to, or severity of, several diseases. It appears that MBL may play an important role in children, who have a relatively immature adaptive immune response. C3 is the point at which all complement pathways converge, and complete deficiency of C3 invariably leads to severe infections, including those caused by meningococci and pneumococci. Deficiencies of the alternative and terminal complement pathways result in an almost exclusive predisposition to invasive meningococcal disease. The spleen plays an important role in antigen processing and the production of antibodies. Splenic macrophages are critical in clearing opsonized encapsulated bacteria (such as pneumococci, meningococci, and Escherichia coli) and intraerythrocytic parasites such as those causing malaria and babesiosis, which explains the fulminant nature of these infections in persons with anatomic or functional asplenia. Paramount to the management of patients with complement deficiencies and asplenia is educating patients about their predisposition to infection and the importance of preventive immunizations and seeking prompt medical attention.

Review of meningococcal group B vaccines

No broadly effective vaccines are available for prevention of group B meningococcal disease, which accounts for >50% of all cases. The group B capsule is an autoantigen and is not a suitable vaccine target. Outer-membrane vesicle vaccines appear to be safe and effective, but serum bactericidal responses in infants are specific for a porin protein, PorA, which is antigenically variable. To broaden protection, outer-membrane vesicle vaccines have been prepared from >1 strain, from mutants with >1 PorA, or from mutants with genetically detoxified endotoxin and overexpressed desirable antigens, such as factor H binding protein. Also, recombinant protein vaccines such as factor H binding protein, given alone or in combination with other antigens, are in late-stage clinical development and may be effective against the majority of group B strains. Thus, the prospects have never been better for developing vaccines for prevention of meningococcal disease, including that caused by group B strains.

Immunodeficiencies

Primary immunodeficiencies (PIDs) are uncommon, chronic and severe disorders of the immune system in which patients cannot mount a sufficiently protective immune response, leading to an increased susceptibility to infections. The treatment of choice for PID patients with predominant antibody deficiency is intravenous immunoglobulin (Ig) replacement therapy. Despite major advances over the last 20 years in the molecular characterization of PIDs, many patients remain undiagnosed or are diagnosed too late, with severe consequences. Various strategies to ensure timely diagnosis of PIDs are in place, and novel approaches are being developed. In recent years, several patient registries have been established. Such registries shed light on the pathology and natural history of these varied disorders. Analyses of the registry data may also reveal which patients are likely to respond well to higher Ig infusion rates and may help to determine the optimal dosing of Ig products. Faster infusion rates may lead to improved convenience for patients and thus increase patient compliance, and may reduce nursing time and the need for hospital resources. Data from two recent studies suggest that Gamunex and Privigen are well tolerated at high infusion rates. Nevertheless, careful selection of patients for high infusion rates, based on co-morbid conditions and tolerance of the current infusion rate, is advisable. Based on the available data, intravenous Ig offers broad protection against encapsulated organisms. As vaccine trends change, careful monitoring of specific antibody levels in the general population, such as those against pneumococcal and meningococcal bacteria, should be implemented.

Seroprevalence of antibodies against fHbp and NadA, two potential vaccine antigens for Neisseria meningitidis

The IgG antibody levels directed against fHbp and NadA, two potential vaccine antigens for Neisseria meningitidis, were examined in order to investigate the extent of natural immunisation against these antigens in different age groups. As a comparison, the IgG antibody levels against Haemophilus influenzae type b were examined. In the two youngest age groups, below 10 years of age, relatively low levels of both anti-fHbp and anti-NadA were measured. A 15-fold higher geometric mean concentration of anti-fHbp was noted in the age group 20-29 years as compared to the age group 15-19 years. The peak concentration was found at 30-39 years, followed by decreased levels with age. Anti-NadA showed a certain increase up to 9 years followed by an even increase up to 40-49 years.

Challenges and progress in the development of a serogroup B meningococcal vaccine

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.

Relative importance of complement-mediated bactericidal and opsonic activity for protection against meningococcal disease

Killing of Neisseria meningitidis can result from complement-mediated serum bactericidal activity (SBA) or opsonophagocytosis (OPA), or a combination of the two mechanisms. While SBA titers > or =1:4 confer protection, recent evidence suggests that this threshold titer may not be required. For example, the incidence of meningococcal disease declines between ages 1 and 4 years without evidence of acquisition of SBA titers > or =1:4. Meningococcal polysaccharide vaccination also elicited OPA and lowered the risk of disease in patients with late complement component deficiencies whose sera did not support SBA. Sera from healthy adults immunized with an outer membrane vesicle vaccine showed OPA killing of N. meningitidis with C6-depleted complement, and whole blood from complement-sufficient non-immunized adults with SBA titers <1:4 also frequently had killing activity. Collectively the data indicate that SBA titers <1:4 and/or vaccine-induced OPA can confer protection against meningococcal disease.

Immunogenicity and tolerability in infants of a New Zealand epidemic strain meningococcal B outer membrane vesicle vaccine

BACKGROUND

An outer membrane vesicle meningococcal vaccine (MeNZB), was developed for the New Zealand epidemic strain of Neisseria meningitidis B:4:P1.7-2,4.

METHODS

A phase II, randomized, observer blind, controlled study evaluating the safety, reactogenicity, and immunogenicity of MeNZB administered with routine New Zealand immunizations at 6 weeks, 3 months, and 5 months of age (n = 375). Group 1 (n = 250) received 25 mug MeNZB and routine immunizations with a fourth MeNZB dose given at 10 months (n = 51). Group 2 (n = 125) received routine immunizations only. Sero-response was a > or =4-fold rise in vaccine strain serum bactericidal antibody titer compared with baseline or a titer of at least 1:8 for baselines <1:4. Reactogenicity was monitored for 7 days after vaccination.

RESULTS

Sero-response in Group 1 was achieved in 53% (95% Confidence interval [CI]: 46-59, n = 239) and 69% (95% CI: 54-80, n = 45) with geometric mean antibody titers of 9 (95% CI: 7-10) and 22 (95% CI: 12-39) after the third and fourth doses, respectively. No negative interference by MeNZB on routine immunizations was detected. There were no serious adverse events judged to be vaccine related.

CONCLUSIONS

In this group of New Zealand infants, 4 MeNZB doses were required to demonstrate titers comparable with those achieved after 3 doses in older children. MeNZB was safe when used concomitantly with routine New Zealand immunizations to 5 months of age.

Impaired maintenance of naturally acquired T-cell memory to the meningococcus in patients with B-cell immunodeficiency

The importance of T cells in the generation of antigen-specific B-cell immunity has been extensively described, but the role B cells play in shaping T-cell memory is uncertain. In healthy controls, exposure to Neisseria meningitidis in the upper respiratory tract is associated with the generation of memory T cells in the mucosal and systemic compartments. However, we demonstrate that in B cell–deficient subjects with X-linked agammaglobulinemia (XLA), naturally acquired T-cell memory responses to meningococcal antigens are reduced compared with healthy control patients. This difference is not found in T-cell memory to an obligate respiratory pathogen, influenza virus. Accordingly, we show that meningococcal antigens up-regulate major histocompatibility complex (MHC) class II, CD40, CD86/80 expression on mucosal and systemic associated B cells and that antigen presentation stimulates T-cell proliferation. A similar reduction in N meningitidis but not influenza antigen–specific T-cell memory was observed in subjects with X-linked hyper IgM syndrome (X-HIM), implicating the interaction of CD40-CD40L in this process. Together, these data implicate B cells in the induction and maintenance of T-cell memory to mucosal colonizing bacteria such as N meningitidis and highlight the importance of B cells beyond antibody production but as a target for immune reconstitution.

Ex vivo model of meningococcal bacteremia using human blood for measuring vaccine-induced serum passive protective activity

The binding of complement factor H (fH) to meningococci was recently found to be specific for human fH. Therefore, passive protective antibody activity measured in animal models of meningococcal bacteremia may overestimate protection in humans, since in the absence of bound fH, complement activation is not downregulated. We developed an ex vivo model of meningococcal bacteremia using nonimmune human blood to measure the passive protective activity of stored sera from 36 adults who had been immunized with an investigational meningococcal multicomponent recombinant protein vaccine. Before immunization, human complement-mediated serum bactericidal activity (SBA) titers of > or = 1:4 against group B strains H44/76, NZ98/254, and S3032 were present in 19, 11, and 8% of subjects, respectively; these proportions increased to 97, 22, and 36%, respectively, 1 month after dose 3 (P < 0.01 for H44/76 and S3032). Against the two SBA-resistant strains, NZ98/254 and S3032, passive protective titers of > or = 1:4 were present in 11 and 42% of sera before immunization, respectively, and these proportions increased to 61 and 94% after immunization (P < 0.001 for each strain). Most of the sera with SBA titers of <1:4 and passive protective activity showed a level of killing in the whole-blood assay (>1 to 2 log(10) decreases in CFU/ml during a 90-min incubation) similar to that of sera with SBA titers of > or = 1:4. In conclusion, passive protective activity was 2.6- to 2.8-fold more frequent than SBA after immunization. The ability of SBA-negative sera to kill Neisseria meningitidis in human blood where fH is bound to the bacteria provides further evidence that SBA titers of > or = 1:4 measured with human complement may underestimate meningococcal immunity.

Absence of mucosal immunity in the human upper respiratory tract to the commensal bacteria Neisseria lactamica but not pathogenic Neisseria meningitidis during the peak age of nasopharyngeal carriage

The normal flora that colonizes the mucosal epithelia has evolved diverse strategies to evade, modulate, or suppress the immune system and avoid clearance. Neisseria lactamica and Neisseria meningitidis are closely related obligate inhabitants of the human upper respiratory tract. N. lactamica is a commensal but N. meningitidis is an opportunistic pathogen that occasionally causes invasive disease such as meningitis and septicemia. We demonstrate that unlike N. meningitidis, N. lactamica does not prime the development of mucosal T or B cell memory during the peak period of colonization. This cannot be explained by the induction of peripheral tolerance or regulatory CD4(+)CD25(+) T cell activity. Instead, N. lactamica mediates a B cell-dependent mitogenic proliferative response that is absent to N. meningitidis. This mitogenic response is associated with the production of T cell-independent polyclonal IgM that we propose functions by shielding colonizing N. lactamica from the adaptive immune system, maintaining immunological ignorance in the host. We conclude that, in contrast to N. meningitidis, N. lactamica maintains a commensal relationship with the host in the absence of an adaptive immune response. This may prolong the period of susceptibility to colonization by both pathogenic and nonpathogenic Neisseria species.

Sampling methods to detect carriage of Neisseria meningitidis; literature review

OBJECTIVES

Studies of meningococcal carriage are important in understanding the epidemiology of meningococcal disease and the impact of vaccination programmes. However, microbiological sampling methods to determine pharyngeal carriage are not consistent between studies and the optimal method is uncertain.

METHODS

A comprehensive literature search was undertaken using Medline, Embase and the Cochrane Library (Feb 2008) to identify studies comparing isolation rates using different sampling methods.

RESULTS

Four studies compared isolation of meningococci from different pharyngeal sites. Nasopharyngeal swabs taken through the nose were less likely to yield meningococcal cultures than pharyngeal swabs taken through the mouth. One study investigated different sampling sites using swabs taken through the mouth and found higher yields from the posterior pharyngeal wall compared to the tonsils (32.2% cf 19.4%, p=0.001). Four studies compared the yield obtained using transport medium to direct plating. Loss of yield in transport medium ranged from 5.7% to 16.4% after storage for >5h.

CONCLUSIONS

The evidence to date suggests that meningococcal carriage should be assessed by swabbing the posterior pharyngeal wall through the mouth, and that swabs should be plated directly on site or placed in transport medium for <5h.

SUMMARY

The current literature suggests meningococcal carriage is best assessed by swabbing the posterior pharyngeal wall through the mouth with direct plating or keeping transport time to below 5h. Whether a swab taken from both the posterior pharynx and the tonsils improves yield further needs evaluation.

Complement-dependent synergistic bactericidal activity of antibodies against factor H-binding protein, a sparsely distributed meningococcal vaccine antigen

BACKGROUND

Antibodies to factor H (fH)-binding protein (fHBP), a meningococcal vaccine antigen, activate classical complement pathway serum bactericidal activity (SBA) and block binding of the complement inhibitor fH.

METHODS

To understand these 2 functions in protection, we investigated the interactions of human complement and 2 anti-fHBP monoclonal antibodies (MAbs) with encapsulated Neisseria meningitidis.

RESULTS

JAR 3 (IgG3) blocks fH binding and elicits SBA against 2 strains with naturally high fHBP expression and a low-expressing strain genetically engineered to express high fHBP levels. JAR 4 (IgG2a) does not block fH binding or elicit SBA. Neither MAb alone elicits SBA against 2 other strains with low fHBP expression, but together the MAbs increase C4b binding and elicit SBA; JAR 3 alone also is bactericidal in whole blood. In nonimmune blood, fHBP knockout mutants from high-expressing stains do not survive, but mutants of low-expressing strains do.

CONCLUSIONS

Expression of fHBP is a prerequisite for bacterial survival in blood only by strains with naturally high fHBP expression. In low-expressing strains, combinations of 2 nonbactericidal anti-fHBP MAbs can bind to nonoverlapping epitopes, engage C1q, activate C4, and mediate classical complement pathway SBA. In the absence of sufficient C4b binding for SBA, an individual MAb can have opsonophagocytic bactericidal activity.

Vaccine-induced opsonophagocytic immunity to Neisseria meningitidis group B

The role of opsonophagocytosis (OP) in protection against meningococcal disease is controversial because patients with deficiencies in terminal complement proteins whose sera support OP but not bactericidal activity (BA) are at greatly increased risk of disease. We assayed complement-mediated BA and OP bactericidal activity in sera from 32 adults immunized with an outer membrane vesicle vaccine given alone or combined with an investigational recombinant protein, genome-derived neisserial antigen (GNA2132). The sera were heat inactivated to remove internal complement activity, and BA was measured with exogenous nonimmune human serum as a complement source. OP was measured with human polymorphonuclear cells (PMNs) and C6-depleted complement, which without PMNs did not support BA. Before immunization, 9 to 19% of sera from subjects in both vaccine groups combined had BA titers of >or=1:4, which increased to 41 to 72% after immunization (P < 0.01 against each of three test strains). The percentages of sera with OP titers of >or=1:5 were 3 to 16%, which increased to 55 to 72% (P < 0.001 for each strain). Most postimmunization BA-positive sera were OP positive, but 10 to 37% of BA-negative sera also were OP positive. Comparing the two vaccine groups, there were no significant differences in the percentages of sera with BA or OP activity except for a higher percentage of OP against one strain in postimmunization sera from subjects in the combination vaccine group (P <or= 0.02). The data support independent roles for serum BA and OP bactericidal activity in protection against group B disease.

Immunity to Neisseria meningitidis group B in adults despite lack of serum bactericidal antibody

Serum-complement-mediated bactericidal antibody (SBA) remains the serologic hallmark of protection against meningococcal disease, despite experimental and epidemiologic data that SBA may underestimate immunity. We measured bactericidal activity against three strains of Neisseria meningitidis group B in sera from 48 healthy adults and in whole blood from 15 subjects. Blood was anticoagulated with lepirudin, a specific thrombin inhibitor not known to activate complement. Depending on the test strain, protective SBA titers of >/=1:4 were present in only 8 to 15% of the subjects, whereas bactericidal activity was present in 40 to 87% of subjects according to the blood assay. Among SBA-negative subjects, blood from 23 to 42% gave a decrease of >/=2 log(10) CFU/ml after 1 h of incubation, and blood from 36 to 83% gave a decrease of >/=1 log(10) after 2 h. For most blood samples, bactericidal antibodies primarily were directed against noncapsular antigens, since activity was not inhibited by group B polysaccharide. For some SBA-negative subjects, white cells were not needed, since similar respective bactericidal activities were observed in blood and plasma. Bactericidal activity by whole blood of SBA-negative subjects can be rapid (<1 h) and effective (>/=2 log(10)) and, among all subjects, was four- to sixfold more prevalent than a positive SBA. Thus, while an SBA titer of >/=1:4 predicts protection against meningococcal disease, a titer of <1:4 is poorly predictive of susceptibility. More sensitive assays than SBA are needed to assess protective meningococcal immunity, or we risk underestimating the extent of immunity in the population and the effectiveness of new meningococcal vaccines.