Protection against group B meningococcal disease. III. Immunogenicity of serotype 2 vaccines and specificity of protection in a guinea pig model

Product review on the IMD serogroup B vaccine Bexsero®

Bexsero® is a multicomponent vaccine composed of four major proteins of Neisseria meningitidis: the fHbp, NHBA, NadA and PorA. This vaccine was licensed against invasive meningococcal disease (IMD) due to serogroup B isolates. When administered alone, Bexsero® showed a safety profile similar to other childhood vaccines. It provides an excellent immunogenicity but that requires booster doses in infants and young children. Although the vaccine does not seem to impact on acquisition of carriage of serogroup B isolates, it confers protection against isolates of serogroup B harboring distinct but cross-reactive variants of fHbp, NadA and NHBA. Primary vaccination schemes in infancy underwent a rapid increase after a toddler booster suggesting an anamnestic response and the establishment of a memory response. As Bexsero® targets sub-capsular proteins that can be conserved regardless the capsule, the vaccine can be effective against non-B isolates such as isolates of serogroups W and X.

Identification of Immunogenic Antigens of Naegleria fowleri Adjuvanted by Cholera Toxin

The intranasal administration of Naegleria fowleri lysates plus cholera toxin (CT) increases protection against N. fowleri meningoencephalitis in mice, suggesting that humoral immune response mediated by antibodies is crucial to induce protection against the infection. In the present study, we applied a protein analysis to detect and identify immunogenic antigens from N. fowleri, which might be responsible for such protection. A Western blot assay of N. fowleri polypeptides was performed using the serum and nasal washes from mice immunized with N. fowleri lysates, either alone or with CT after one, two, three, or four weekly immunizations and challenged with trophozoites of N. fowleri. Immunized mice with N. fowleri plus CT, after four doses, had the highest survival rate (100%). Nasal or sera IgA and IgG antibody response was progressively stronger as the number of immunizations was increased, and that response was mainly directed to 250, 100, 70, 50, 37, and 19 kDa polypeptide bands, especially in the third and fourth immunization. Peptides present in these immunogenic bands were matched by nano-LC–ESI-MSMS with different proteins, which could serve as candidates for a vaccine against N. fowleri infection.

Prevalence of factor H Binding Protein sub-variants among Neisseria meningitidis in China

OBJECTIVE

To study the prevalence of the fHbp genes in Neisseria meningitidis (N. meningitidis) isolates for further evaluation and development of serogroup B meningococcal vaccines in China.

METHODS

A panel of 1012 N. meningitidis strains was selected from the national culture collection from 1956 to 2016, according to the years of isolation, locations, and strain sources. These were tested by FHbp variant typing. Multi-locus sequence typing (MLST) was performed on 822 of these samples, including 242 strains from clinical strains and 580 carrier-derived strains. Analysis based on sequence types, serogroups, and FHbp variations were used to summarize the prevalence and characteristics of N. meningitidis.

RESULTS

There were 8 serogroups of N. meningitidis as well as a collection of nongroupable strains in this study. 1008 of 1012 N. meningitidis strains tested were positive for the fHbp gene. Serogroup A N. meningitidis (MenA) strains belonging to ST-1 and ST-5 clonal complexes harbored genes only encoding variant 1 (v1) FHbp. All MenW strains encoded v2 FHbp. 61.9% of clinical MenB strains were positive for v2 FHbp vs. 32.1% that were positive for v1. Among fHbp-positive carrier-derived MenB strains, v2 FHbp accounted for 90.8%. 79.7% of clinical MenC strains were positive for v1 FHbp and 20.3% were positive for v2 FHbp. Among carrier-derived MenC strains, v2 FHbp predominated. The number of major serogroups of N. meningitidis analyzed by MLST was 822, and the encoded FHbp showed CC- or ST-specific characteristics.

CONCLUSION

fHbp genes were detected in almost all N. meningitidis strains in this study. Therefore, it is possible that a vaccine against MenB or meningococci irrespective of serogroups, which includes FHbp, could be developed. Meningococcal vaccine development for China is a complex issue and these findings warrant further attention with respect to vaccine development.

Potential Roles of Fungal Extracellular Vesicles during Infection

Extracellular vesicles (EVs) are produced by virtually all cell types. Within the past few years, work in this field has revealed more information about fungal EVs. Fungal EVs have been shown to carry proteins, lipids, pigments, polysaccharides, and RNA; these components are known virulence factors, a fact which supports the hypothesis that fungal EVs concentrate pathogenic determinants. Additionally, recent studies have demonstrated that fungal EVs stimulate the host immune system. In this review, putative roles of fungal EVs are discussed, including their potential as vaccination tools and their possible contribution to pathogenesis in invasive fungal diseases.

Bexsero® chronicle

Neisseria meningitidis causes globally 1·2 million invasive disease cases and 135,000 deaths per year, mostly in infants and adolescents. A century of traditional vaccinology had failed the fight against the serogroup B meningococcus (MenB), mostly prevalent in developed countries. Eighteen years after the publication of the first complete genome sequence from a living organism, thanks to an innovative genome-based approach named 'reverse vaccinology', the first broadly effective MenB vaccine was licensed for use by the European Medical Agency and other authorities, and is being implemented worldwide. Here we review this long and passionate journey, from the disease epidemiology to novel antigen discovery, from vaccine clinical development to public health impact: two decades of scientific and technological innovation to defeat one of the most sudden and devastating invasive diseases.

Vaccines against meningococcal serogroup B disease containing outer membrane vesicles (OMV): lessons from past programs and implications for the future

The utility of wild-type outer membrane vesicle (wtOMV) vaccines against serogroup B (MenB) meningococcal disease has been explored since the 1970s. Public health interventions in Cuba, Norway and New Zealand have demonstrated that these protein-based vaccines can prevent MenB disease. Data from large clinical studies and retrospective statistical analyses in New Zealand give effectiveness estimates of at least 70%. A consistent pattern of moderately reactogenic and safe vaccines has been seen with the use of approximately 60 million doses of three different wtOMV vaccine formulations. The key limitation of conventional wtOMV vaccines is their lack of broad protective activity against the large diversity of MenB strains circulating globally. The public health intervention in New Zealand (between 2004–2008) when MeNZB was used to control a clonal MenB epidemic, provided a number of new insights regarding international and public-private collaboration, vaccine safety surveillance, vaccine effectiveness estimates and communication to the public. The experience with wtOMV vaccines also provide important information for the next generation of MenB vaccines designed to give more comprehensive protection against multiple strains.

Bactericidal antibody is the immunologic surrogate of protection against meningococcal disease

It has been demonstrated that antibodies induced by meningococcal polysaccharide, polysaccharide-protein conjugates and outer membrane protein vaccines protect against meningococcal disease. This review will show that the induced antibody protects via complement mediated bactericidal killing and that induction of serum bactericidal antibody (SBA) is a good surrogate for efficacy. The critical role of SBA is shown by: (1) Highest incidence of meningococcal disease occurs in infants between 6 and 18 months of age, who have the lowest levels of SBA. (2) Studies published in 1969 in US Army recruits showed a direct correlation between susceptibility to meningococcal disease and absence of SBA. (3) Meningococcal polysaccharide, polysaccharide-protein conjugates, and outer membrane vesicle vaccines all induce SBA shown to be effective in direct proportion to the percent of vaccinees with SBA activity.

A novel method to screen genomic libraries that combines genomic immunization with the prime-boost strategy

We employed a prime-boost regimen in combination with the expression library immunization protocol to improve the protective effectiveness of a genomic library used as immunogen. To demonstrate the feasibility of this novel strategy, we used as a prime a serogroup B Neisseria meningitidis random genomic library constructed in a eukaryotic expression vector. Mice immunized with different fractions of this library and boosted with a single dose of meningococcal outer membrane vesicles elicited higher bactericidal antibody titers compared with mice primed with the empty vector. After the boost, passive administration of sera from mice primed with two of these fractions significantly reduced the number of viable bacteria in the blood of infant rats challenged with live N. meningitidis. The method proposed could be applied to the identification of subimmunogenic antigens during vaccine candidate screening by employing expression library immunization.

Prospects for vaccine prevention of meningococcal infection

Neisseria meningitidis is the leading cause of bacterial meningitis in the United States and worldwide. A serogroup A/C/W-135/Y polysaccharide meningococcal vaccine has been licensed in the United States since 1981 but has not been used universally outside of the military. On 14 January 2005, a polysaccharide conjugate vaccine that covers meningococcal serogroups A, C, W-135, and Y was licensed in the United States for 11- to 55-year-olds and is now recommended for the routine immunization of adolescents and other high-risk groups. This review covers the changing epidemiology of meningococcal disease in the United States, issues related to vaccine prevention, and recommendations on the use of the new vaccine.

Are antibodies to the capsular polysaccharide of Neisseria meningitidis group B and Escherichia coli K1 associated with immunopathology?

As polysialic acid (PSA), the capsule of Group B meningococcus (GBM) and Escherichia coli K1, is a component of mammalian glycopeptides, there is concern that vaccines against PSA could induce immunopathology. Purified PSA is not immunogenic; however, as a component of bacteria or bound to proteins, it induces protective antibodies. In this review, we did not unearth data indicating an association of IgG anti-PSA with immunopathology in experimental animals or humans. We found no increased incidence of autoimmunity from GBM infections in our review of the natural history/sequellae of Neisseria meningitis infections. Accordingly, we propose that clinical trials of PSA conjugate vaccines, be considered.

Effect of antigen coating conditions on enzyme-linked immunosorbent assay for detection of immunoglobulin G antibody to Neisseria meningitidis serogroup Y and W135 capsular polysaccharide antigens in serum

Human sera collected from 28 consenting adult volunteers were used to define assay conditions for meningococcal vaccine clinical trial serology. Immunoassay parameters were optimized with these test sera and the standard reference serum, CDC1992. Coating conditions for serogroup Y and W135 polysaccharide antigens were found to influence the predicted serum immunoglobulin G (IgG) antibody concentrations. Sera that displayed IgG antibody binding profiles most unlike that of CDC1992 were influenced the most by coating conditions. Our results suggest that presentation of specific epitopes is influenced by antigen-coating concentrations for serogroup Y and W135 polysaccharides.

Immune response to native NadA from Neisseria meningitidis and its expression in clinical isolates in Brazil

A mAb against the NadA protein from Neisseria meningitidis strain 3006 (serosubtype B : 2b : P1.2 : P5.2,8) demonstrated strong bactericidal activity against Brazilian epidemic serogroup B strain N44/89 (B : 4,7 : P1.19,15 : P5.5,7) and a serogroup C strain, IMC 2135 (C : 2a : P1.5,2), but not against another serogroup C strain, N1002/90 (C : 2b : P1.3 : P5.8). The immunogenicity of native NadA in an outer-membrane vesicle (OMV) preparation was also tested. Serum from mice immunized with OMV from serogroup B strain N44/89, which contains the NadA protein, showed bactericidal activity against serogroup B and C strains possessing NadA. In dot-blot analysis of 100 serogroup B and 100 serogroup C isolates from Brazilian patients, the mAb to NadA recognized about 60 % of the samples from both serogroups. The molecular mass of the NadA protein from strain N44/89 determined by mass spectrometry was 37 971 Da and the peptide sequences were identical to those of NadA from N. meningitidis strain MC58.

A glycoconjugate vaccine for Neisseria meningitidis induces antibodies in human infants that afford protection against meningococcal bacteremia in a neonate rat challenge model

The functional activities of serum samples from human infants immunized with a glycoconjugate vaccine for Neisseria meningitidis serogroup C were assessed in a complement-mediated antibody-dependent serum bactericidal assay (SBA) and in a neonate rat model of protection from bacteremia. Selective serum samples from individual human infants were combined to make a panel of 11 serum pools to obtain a sufficient volume for testing. Each pool was assayed (i) for the anti-N. meningitidis serogroup C capsular polysaccharide (PS) immunoglobulin G (IgG) concentration as determined by reactivity in a direct-binding enzyme-linked immunosorbent assay, (ii) for bactericidal activity against N. meningitidis serogroup C strain C11, and (iii) for the ability to reduce bacteremia after passive transfer into a neonate rat model. Representative serum samples from infants who were not previously immunized with any N. meningitidis serogroup C vaccine served as a negative control. The prepared serum pools ranged in antibody concentration from 0.18 to 17.31 micro g of IgG specific for N. meningitidis serogroup C PS per ml. For this serum panel, a direct relationship between concentrations of anti-N. meningitidis serogroup C PS-specific IgG and serum SBA titers (r = 0.9960) was observed. Passive transfer to neonate rats demonstrated the ability of postimmunization serum samples to significantly reduce (> or =2-log(10) reduction compared to control animals) the level of bacteremia following a challenge. Of 79 neonate rats that received > or =0.031 micro g of human infant anti-N. meningitidis serogroup C PS IgG, 75 (94.9%) had a > or =2-log(10) reduction in bacteremia, whereas of the animals that received <0.031 micro g of antigen-specific IgG, 10.3% (4 of 39 rats) showed a > or =2-log(10) reduction in bacteremia. It was concluded that the anti-N. meningitidis serogroup C PS IgG antibody induced by this glycoconjugate vaccine had in vitro functional activity (as determined by a SBA) and also afforded protection against meningococcal bacteremia in an animal model.

Standardization of Neisseria meningitidis serogroup B colorimetric serum bactericidal assay

The correlate of protection for serogroup B meningococci is not currently known, but for serogroup C it is believed to be the serum bactericidal assay (SBA). The current SBAs are labor intensive and the variations in protocols among different laboratories make interpretation of results difficult. A colorimetric SBA (cSBA), based on the ability of Neisseria meningitidis serogroup B to consume glucose, leading to acid production, was standardized by using group B strain Cu385-83 as the target. The cSBA results were compared to those obtained for a traditional colony-counting microassay (mSBA). Glucose and bromocresol purple pH indicator were added to the medium in order to estimate growth of cSBA target cell survivors through color change. Different variants of the assay parameters were optimized: growth of target cells (Mueller Hinton agar plates), target cell number (100 CFU/per well), and human complement source used at a final concentration of 25%. After the optimization, three other group B strains (H44/76, 490/91, and 511/91) were used as targets for the cSBA. The selection of the assay parameters and the standardization of cSBA were done with 13 sera from vaccinated volunteers. The titers were determined as the higher serum dilution that totally inhibited the bacterial growth marked by the color invariability of the pH indicator. This was detected visually as well as spectrophotometrically and was closely related to a significant difference in the growth of target cell survivors determined using Student's t test. Intralaboratory reproducibility was +/-1 dilution. The correlation between bactericidal median titers and specific immunoglobulin G serum concentration by enzyme immunoassay was high (r = 0.910, P < 0.01). The bactericidal titers generated by the cSBA and the mSBA were nearly identical, and there was a high correlation between the two assays (r = 0.974, P < 0.01). The standardized cSBA allows easy, fast, and efficient evaluation of samples.

Genetic and immunologic characterization of a novel serotype 4, 15 strain of Neisseria meningitidis

The porin proteins of Neisseria meningitidis are important components of outer membrane protein (OMP) vaccines. The class 3 porin gene, porB, of a novel serogroup B, serotype 4, 15 isolate from Chile (Ch501) was found to be VR1-4, VR2-15, VR3-15 and VR4-15 by porB variable region (VR) typing. Rabbit immunization studies using outer membrane vesicles revealed immunodominance of individual PorB (class 3) VR epitopes. The predominant anti-Ch501 PorB response was directed to the VR1 epitope. Anti-PorB VR1 mediated killing was suggested by the bactericidal activity of Ch501 anti-sera against a type 4 strain not expressing PorA or class 5 OMPs. Studies that examine the molecular epidemiology of individual porB VRs, and the immune responses to PorB epitopes, may contribute to the development of broadly protective group B meningococcal vaccines.

Detection of complement-mediated antibody-dependent bactericidal activity in a fluorescence-based serum bactericidal assay for group B Neisseria meningitidis

Serum bactericidal assays (SBAs) for Group B meningococci are considered the methods of choice for the evaluation of functional antimeningococcal antibodies. Many investigators regard SBAs as time- and labor-intensive. Variations in SBA protocols among different laboratories make interpretation of results difficult. Here we describe a fluorescence-based serum bactericidal assay (fSBA) and compare the results obtained with the fSBA to the results obtained with a more conventional SBA. The results generated by both assays were dependent upon the surviving bacteria after incubation, and the assay mixtures contained identical components. Differences between assays lie in how the surviving bacteria are quantified. The fSBA described in the paper uses the fluorescent dye alamarBlue (M. V. Lancaster and R. D. Fields, U.S. patent 5501959, March 1996). The fluorescent signals generated in the fSBA correlate to the oxidative respiration of surviving bacteria. Viable bacteria were detected between 6 and 8 h directly from reaction mixtures in 96-well plates by the fSBA, whereas colonies isolated on semisolid media could be counted after 24 h of incubation. The bactericidal titers generated by both assays were nearly identical. The fSBA described here can be used as an assay for the screening of large quantities of individual sera as complement sources or as a method for the detection of functional antibodies directed against group B Neisseria meningitidis in both human and mouse antisera.

Humoral immune responses to Neisseria meningitidis in children

An understanding of the nature of immunity to serogroup B meningococci in childhood is necessary in order to establish the reasons for poor responses to candidate vaccines in infancy. We sought to examine the nature of humoral immune responses following infection in relation to age. Serum bactericidal activity was poor in children under 12 months of age despite recent infection with Neisseria meningitidis. The highest levels of bactericidal activity were seen in children over 10 years of age. However, infants produced levels of total immunoglobulin G (IgG) and IgG subclass antibodies similar to those in older children in a meningococcal enzyme-linked immunosorbent assay. Most antibody was of the IgG1 and IgG3 subclasses. This striking age dependency of bactericidal antibody response following infection is not apparently due to failure of class switching in infants but might be due to qualitative differences in antibody specificity or affinity.

Immunization with recombinant class 1 outer-membrane protein from Neisseria meningitidis: influence of liposomes and adjuvants on antibody avidity, recognition of native protein and the induction of a bactericidal immune response against meningococci

The porA gene from Neisseria meningitidis was cloned into the pRSETA vector and recombinant class 1 outer-membrane protein expressed at high levels in Escherichia coli. The protein was readily purified by affinity chromatography on a Ni2+ matrix and used for immunization of mice with conventional AI(OH)3 adjuvant, with experimental adjuvants which have the potential for human use, and with liposomes. The resulting sera were analysed for the magnitude, subclass distribution and antigenic specificity of the immune response. In addition, surface plasmon resonance (SPR) was used to quantify antibody avidity by analysis of the kinetics of binding to native class 1 protein. Immunization with conventional and experimental adjuvants induced antibodies of low avidity that did not recognize native class 1 protein. In contrast, immunization with recombinant protein in liposomes induced antibodies of high avidity which recognized native class 1 protein, as measured by their ability to label meningococcal cells in immunofluorescence assays and to inhibit the binding of a protective mAb. These properties were associated with the presence in sera of high levels of antibodies with the ability to induce complement-mediated killing of meningococci. These data show that liposomes containing recombinant class 1 protein represent a potential basis of future vaccines, of defined composition, designed for the prevention of group B meningococcal infections.

Standardization and a multilaboratory comparison of Neisseria meningitidis serogroup A and C serum bactericidal assays. The Multilaboratory Study Group

A standardized serum bactericidal assay (SBA) is required to evaluate the functional activity of antibody produced in response to Neisseria meningitidis serogroup A and C vaccines. We evaluated assay parameters (assay buffer, target strains, growth of target cells, target cell number, complement source and concentration, and methods for growth of surviving bacteria) which may affect the reproducibility of SBA titers. The various assay parameters and specificity of anticapsular antibody to five serogroup A strains (A1, ATCC 13077, F8238, F9205, and F7485) and four serogroup C strains (C11, G7880, G8050, and 1002-90) were evaluated with Centers for Disease Control and Prevention meningococcal quality control sera. The critical assay parameters for the reproducible measurement of SBA titers were found to include the target strain, assay incubation time, and complement. The resulting standardized SBA was used by 10 laboratories to measure functional anticapsular antibody against serogroup A strains F8238 and serogroup C strain C11. In the multilaboratory study, SBA titers were measured in duplicate for 14 pairs of sera (seven adults and seven children) before and after immunization with a quadrivalent polysaccharide (A, C, Y, and W-135) vaccine. The standardized SBA was reliable in all laboratories regardless of experience in performing SBAs. For most sera, intralaboratory reproducibility was +/- 1 dilution; interlaboratory reproducibility was +/- 2 dilutions. The correlation between median titers (interlaboratory) and enzyme-linked immunosorbent assay total antibody concentrations was high for both serogroup A (r = 0.86; P < 0.001; slope = 0.5) and serogroup C (n = 0.86; P < 0.001; slope = 0.7). The specified assay, which includes the critical parameters of target strain, incubation time, and complement source, will facilitate interlaboratory comparisons of the functional antibody produced in response to current or developing serogroup A and C meningococcal vaccines.

Binding diversity of monoclonal antibodies to alpha(2-->8) polysialic acid conjugated to outer membrane vesicle via adipic acid dihydrazide

Murine monoclonal antibodies (mAbs) were generated using group B Neisseria meningitidis and Escherichia coli K1 polysaccharides (PSs) conjugated to outer membrane vesicle (OMV) via adipic acid dihydrazide, and were used to identify the immunodeterminants expressed on these capsular PSs. Ten mAbs representative of IgM and all subclasses of IgG were obtained which recognized diverse immunodeterminants on alpha(2-->8) polysialic acid (PSA). The specificity of mAbs to different antigenic determinants was assessed by their differential binding to PSA attached to a solid phase by different methods and confirmed by absorption studies. Two mAbs from the E. coli K1 fusion were directed to the O-acetyl epitope and the rest reacted with both the PSs only when attached to a solid phase by certain means. The methods by which PSA was coated on the solid phase had an impact on the epitope expression and binding pattern. At the concentrations used, the O-acetyl-specific mAbs, IgG1 and IgG3 mAbs were not bactericidal against group B N. meningitidis, whereas other mAbs were. The conjugates B and K1 PSs present to the murine immune system different antigenic determinants, some of which elicit bactericidal antibodies.

Comparison among opsonic activity, antimeningococcal immunoglobulin G response, and serum bactericidal activity against meningococci in sera from vaccinees after immunization with a serogroup B outer membrane vesicle vaccine

Opsonic activity in sera from 27 military recruits vaccinated with the Norwegian meningococcal serogroup B outer membrane vesicle vaccine was measured as respiratory burst with polymorphonuclear leukocytes as the effector cells and meningococci of the epidemic strain as the target. The results were compared with antimeningococcal IgG antibodies against an outer membrane vesicle coat in an enzyme-linked immunosorbent assay and with serum bactericidal activity. The vaccinees were immunized twice, with a 6-week interval between the two. The serum samples studied were collected at day zero, after 6 weeks, and after 12 weeks. Both serum bactericidal activity and respiratory burst were measured by adding external serum as the complement source. The results revealed a significant increase in specific IgG response, serum bactericidal activity, and respiratory burst after vaccination. We found a highly significant correlation between the responses in all three assays (P < 0.0001). The highest correlation was found between respiratory burst and antimeningococcal IgG response (r = 0.93). This result strongly indicates that respiratory burst is mediated almost exclusively by IgG antibodies. The correlation between antimeningococcal IgG response and serum bactericidal activity was slightly lower (r = 0.83). The correlation between respiratory burst and serum bactericidal activity was further reduced (r = 0.78), and some of the sera revealed a marked preference for only one of the activities. This result means that respiratory burst and serum bactericidal activity in part are induced by different mediators, and to obtain a more complete picture of the potential protective activity, both assays should be applied to survey a vaccine trial.

Surface antigen analysis of group B Neisseria meningitis outer membrane by monoclonal antibodies: identification of bactericidal antibodies to class 5 protein

Twenty-four monoclonal antibodies (mAbs) against group B Neisseria meningitidis surface antigens were analyzed by immunoenzymatic assays and by a bactericidal test. Two mAbs were specific to polysaccharide B and one to lipopolysaccharide. The others were specific to polysaccharide B and one to lipopolysaccharide. The others were directed against outer membrane proteins ranging in molecular mass from 25 to 200 kDa. The outer membrane protein epitopes recognized by the mAbs were not conformational and were located on the outer surface of the microorganism. Linear epitopes on the class 5 protein, exposed on the surface of the membrane, were able to induce bactericidal antibodies to the homologous strain. The susceptibility of Neisseria meningitidis to these antibodies was unchanged when this organism was cultivated under conditions of iron depletion. These results demonstrate that peptides derived from class 5 proteins are potentially important in synthetic peptide or in recombinant protein vaccines containing linear bactericidal epitopes.

Assignment of Neisseria meningitidis serogroup A and C class-specific anticapsular antibody concentrations to the new standard reference serum CDC1992

A new standard meningococcal reference serum designated CDC1992 was prepared to replace meningococcal reference sera ECG and PB-2, which are not available in sufficient quantities for continued use as primary reference sera. CDC1992 was prepared from 14 healthy adult volunteers who underwent plasmapheresis 4 to 12 weeks postvaccination with a single dose of a Neisseria meningitidis quadrivalent polysaccharide vaccine. Total and/or class-specific meningococcal serogroup A and C anticapsular antibody concentrations (in micrograms per milliliter) were assigned to CDC1992 by using homologous and heterologous enzyme-linked immunosorbent assay (ELISA) formats. The reference serum ECG was used as a reference standard to assign total anticapsular antibody concentrations to CDC1992 by a homologous ELISA format. A heterologous ELISA format, with the Haemophilus influenzae type b standard reference serum FDA 1983, was used to assign total and class-specific antibody concentrations to CDC1992. Alkaline phosphatase-labeled mouse anti-human monoclonal antibody conjugates were used as secondary antibodies in both ELISA formats. The total, immunoglobulin G (IgG), IgA, and IgM antibody concentrations, assigned to CDC1992 for serogroup A were 135.8, 91.8, 20.1, and 23.9 micrograms/ml, respectively, and those for serogroup C were 32.0, 24.1, 5.9, and 2.0 micrograms/ml, respectively. Meningococcal serogroup A and C antibody concentrations were in good agreement when homologous and heterologous ELISA format results were compared. Total and class-specific serogroup A and C antibody concentrations were determined in six adult quality control serum samples from the Centers for Disease Control and Prevention by using the homologous ELISA and our assigned antibody concentrations for CDC1992. Antibody concentrations in reference sera ECG and PB-2 were measured in order to provide a historical link to previous studies. The general acceptance of CDC1992 as the standard reference serum and the assigned antibody concentrations will allow investigators to compare antibody levels in serum to those in a single reference preparation.

Immune response of Brazilian children to a Neisseria meningitidis serogroup B outer membrane protein vaccine: comparison with efficacy

Since 1986, serogroup B Neisseria meningitidis has caused approximately 80% of the meningococcal disease in Brazil. In 1988, an epidemic caused by N. meningitidis B:4:P1.15 was recognized in the greater São Paulo area of Brazil. The São Paulo state government decided to vaccinate children from 3 to 83 months of age with a vaccine consisting of serotype 4 outer membrane protein and group C meningococcal polysaccharide that was produced in Cuba. About 2.7 million children were vaccinated during two immunization campaigns conducted in 1989 and 1990. Because of this, a case-control study was designed to determine vaccine efficacy against group B meningococcal disease. The purpose of our study was to compare the antibody response with the protection from disease estimated from the case-control study. We measured the immune responses of vaccinees by enzyme-linked immunosorbent assay (ELISA), immunoblot, and bactericidal assay. The development of bactericidal antibodies was age dependent and in good agreement with the results of the case-control study. Only 40% of vaccinees showed fourfold or greater increases in bactericidal antibody titers after vaccination. A poor correlation between antibody levels detected by ELISA and those by bactericidal assay was found. Immunoblot analysis showed that about 50% of the serum samples with bactericidal titers higher than 1:4 were reactive with class 1 outer membrane protein. We conclude that the bactericidal assay is a good, laboratory-based, functional assay for the study of vaccine immunogenicity and that an effective solution to group B meningococcal disease remains to be demonstrated.

Involvement of phospholipid end groups of group C Neisseria meningitidis and Haemophilus influenzae type b polysaccharides in association with isolated outer membranes and in immunoassays

There are several bacterial polysaccharides (PSs) which contain a terminal lipid moiety. It has been postulated that these terminal lipid moieties anchor the PSs to the outer membrane of the bacteria. Our studies have shown that incubation of native PS from group C Neisseria meningitidis or Haemophilus influenzae type b with isolated outer membrane vesicles results in association of a portion of the PS with the vesicles. Removal of the terminal lipid from the PS by treatment with phospholipase A2 or phospholipase D eliminates this association. In other studies, it was shown that delipidated PSs are not suitable as solid-phase antigens in a currently used enzyme-linked immunosorbent assay (ELISA). Measurement of antibody units in the reference sera by using delipidated PSs as antigens in an ELISA yielded negligible absorbance compared with native PSs when methylated human serum albumin was used to coat the PSs to the plate. Nevertheless, phospholipase A2 and phospholipase D treatment did not noticeably affect antigenic epitopes, since soluble group C PS without the terminal lipid bound antibody as effectively as the native PS did, as measured by a competitive inhibition assay. Both hydrophobic and electrostatic interactions are important for the binding of group C N. meningitidis PS to the ELISA plate, while charge interactions seem to be sufficient for binding the more negatively charged H. influenzae type b PS.

Specificity of antibodies to O-acetyl-positive and O-acetyl-negative group C meningococcal polysaccharides in sera from vaccinees and carriers

Most group C Neisseria meningitidis strains produce an O-acetyl-positive polysaccharide, a homopolymer of alpha-2----9-linked N-acetylneuraminic acid with O-acetyl groups at the C-7 and C-8 of its sialic acid residues. The majority of disease isolates have been reported to contain this polysaccharide. Some strains produce group C polysaccharide lacking O-acetyl groups. The licensed vaccine contains the O-acetyl-positive polysaccharide. We have measured the antibody specificities to the two polysaccharides in sera from asymptomatic group C meningococcal carriers and vaccinated adults by a new enzyme-linked immunosorbent assay (ELISA) procedure using methylated human serum albumin for coating the group C polysaccharide onto microtiter plates. Inhibition of binding of serum antibodies to polysaccharide-coated plates was measured by ELISA after incubation with O-acetyl-positive and O-acetyl-negative group C polysaccharides. Greater inhibition of binding of carrier sera was observed with the homologous polysaccharide. There was substantial inhibition of binding of vaccinee sera to the O-acetyl-positive polysaccharide-coated plate following preincubation with O-acetyl-positive polysaccharide, but homologous inhibition on plates coated with the O-acetyl-negative polysaccharide required much higher concentrations of polysaccharide. Carrier sera may have a higher proportion of antibodies with greater specificity for the O-acetyl-negative polysaccharide, while vaccinee sera contain antibodies with greater affinity for the O-acetyl-positive polysaccharide. Studies with monoclonal antibodies specific for O-acetyl-positive and O-acetyl-negative polysaccharides reveal that the percentage of group C meningococcal disease caused by O-acetyl-negative strains remains about 15%, as found over 15 years ago.

Expression of Neisseria meningitidis iron-regulated outer membrane proteins, including a 70-kilodalton transferrin receptor, and their potential for use as vaccines

The iron-regulated proteins (IRPs) of five group B meningococcal strains expressing class 2 outer membrane proteins were compared with those of five strains expressing class 3 proteins. Three to four high-molecular-weight IRPs were expressed by each strain, but their molecular sizes varied between strains and were not related to class 2 or 3 protein expression. Transferrin and hemoglobin could be used as a sole iron source. By using anti-human transferrin antibodies, it was shown that meningococcal cells and purified outer membranes bound transferrin. Growth under conditions of iron limitation caused a several-fold increase in the amount of transferrin bound to the cell surface. The transferrin-binding protein was detergent solubilized from outer membranes and partially purified. The isolated protein bound human transferrin and had an apparent molecular mass of 70 kilodaltons. To evaluate the potential of vaccines containing IRPs, we prepared outer membrane vaccines from strains M986-NCV-1 (M986) (--:2a: P1.2) and 44/76-M25 (44/76) (--:15:P1.15) grown to fully express their IRPs. Both vaccines induced significant anti-IRP antibodies as measured by enzyme immunoassay and by Western immunoblot with both M986 and 44/76 outer membranes. By Western blot analysis, the M986 vaccine induced antibodies to two different IRPs, one of which was shared with 44/76. Since the IRPs are major in vivo-expressed outer membrane proteins and are required for survival in vivo, these proteins should be evaluated for their usefulness in a group B meningococcal vaccine.

Immunoglobulin V regions of a bactericidal anti-Neisseria meningitidis outer membrane protein monoclonal antibody

C6 is a potentially therapeutic murine monoclonal antibody that recognizes the class 1 outer membrane protein of Neisseria meningitidis. C6 specifically immunoblots this antigen and augments in vitro killing of N. meningitidis bacteria. We describe a general method of obtaining the heavy and light chain variable-region sequence from immunoglobulin-secreting cells. The method uses mixed polymerase chain reaction (PCR) primers designed from the 5' end of the framework 1 (FR1) sequences of the heavy and light chains, and 3'-end primers for constant-region conserved sequences. The method has been applied to the cloning and sequencing of the variable region of C6 to construct a humanized monoclonal antibody. Rapid amplification and sequencing of variable regions by this general method have multiple applications in the study of the immune response to infectious diseases.

Sequence of the structural gene (rmpM) for the class 4 outer membrane protein of Neisseria meningitidis, homology of the protein to gonococcal protein III and Escherichia coli OmpA, and construction of meningococcal strains that lack class 4 protein

The structural gene (rmpM) of the class 4 outer membrane protein of Neisseria meningitidis has been cloned and sequenced. The derived amino acid sequence reveals a 218-amino-acid protein following a 22-amino-acid signal peptide. The protein shows 94.2% homology with protein III of Neisseria gonorrhoeae and shares its two potential disulfide loops. The protein also shares limited homology with Escherichia coli OmpA. N. gonorrhoeae protein III has been shown to elicit blocking antibodies that prevent the killing of serum-resistant strains by immune sera (P. A. Rice, H. E. Vayo, M. R. Tam, and M. S. Blake, J. Exp. Med. 164:1735-1748, 1986). The very close homology of meningococcal class 4 protein with gonococcal protein III suggests that meningococcal outer membrane preparations containing class 4 protein may similarly stimulate blocking antibodies. In order to investigate the role of the class 4 protein in the pathogenesis of meningococcal infection, we have used an erythromycin resistance gene in developing two meningococcal strains that lack class 4 protein.

Serum opsonins to serogroup B meningococci in meningococcal disease

The opsonic activity to serogroup B meningococci (B:15:P1.16) was measured in sera from 101 patients with meningococcal disease using a chemiluminescence method. On admission to hospital the opsonic activity was lower in 12 patients who died than in survivors (p = 0.0007). A close association was observed between the opsonic activity and the duration of symptoms before admission, the severity of the disease, and the levels of IgG antibodies to the outer membrane complex (15:P1.16). The opsonic activity was low in 2 premorbid sera compared to healthy controls. The mean opsonic activity peaked 2 weeks after admission and was still high 3-5 years later. Meningococcal strains of different serogroups, serotypes and subtypes induced a similar increase in opsonic activity to B:15:P1.16 meningococci. No increase in activity was observed in sera from patients with meningitis and septicemia caused by other bacteria. Serum opsonins seem to be of significant importance in the host defence against serogroup B meningococci.

Antibody responses to serogroup B meningococcal outer membrane antigens after vaccination and infection

Antibody responses of adult volunteers given a vaccine containing meningococcal capsular polysaccharides (serogroups A, C, Y, and W-135) noncovalently complexed with serotype 2b:P1.2 and 15:P1.16 outer membrane proteins have been studied. Sera were analyzed by enzyme-linked immunosorbent assay methods for immunoglobulin G (IgG), IgM, and IgA antibodies and for bactericidal activities against the homologous strains. The vaccination was performed as a double-blind experiment with 47 volunteers, of whom 23 received the protein-polysaccharide vaccine and 24 received the control preparation containing the polysaccharides only. Ten additional persons volunteered for the protein-polysaccharide vaccine. Before vaccination, carriers of meningococci had significantly higher levels of specific IgG and IgA and also higher bactericidal activities than noncarriers. At 2 weeks postvaccination we found significant IgG and bactericidal antibody responses against both the 2b:P1.2 and 15:P1.16 strains in about 70% of the protein-polysaccharide vaccinees. The immune response induced by disease was compared with that induced by vaccination by analyzing paired sera from 13 survivors of serogroup B serotype 15 meningococcal disease. We found that the mean specific IgG level in acute-phase sera was lower than average in prevaccination sera from the vaccinees but similar to that of healthy noncarriers before vaccination. The convalescent-phase sera showed IgG responses similar to those of the vaccinees, but the IgM response to disease was significantly higher than after vaccination. The immune response to disease caused by serogroup B serotype 15 meningococci was found by enzyme-linked immunosorbent assay analysis to be about the same with outer-membrane antigens from a serotype 2b strain as it was with antigens from a serotype 15 strain.

Identification of immunogenic outer membrane proteins of Pasteurella multocida 3:A in rabbits

Four groups of protective rabbit immune sera were used to identify Pasteurella multocida outer membrane immunogens by a radioimmunoprecipitation procedure and Western blot (immunoblot) analysis. These are rabbit hyperimmune sera against KSCN extract of P. multocida (group 1) and rabbit immune sera against the KSCN extract of P. multocida (group 2), the outer membrane of P. multocida (group 3), and live P. multocida cells (group 4). Rabbits mounted an antibody response to 18 proteins found in the outer membrane of P. multocida, and the major antibody activities were directed to the 27,000-molecular-weight outer membrane protein (27K protein), as well as the 37.5K, 49.5K, 58.7K, and 64.4K outer membrane proteins. These outer membrane immunogens appear to be exposed on the cell surface and accessible to antibodies, since adsorption of these immune sera with intact P. multocida cells resulted in a significant reduction of antibody activities directed against these proteins, especially the 37.5K protein. Antibodies eluted from immune serum-P. multocida cell complexes were reactive to the 37.5K immunogen, confirming that this protein is exposed on cell surface and accessible to antibodies. Western blot analyses with group 1, 3, and 4 immune sera confirmed that the 27K, 37.5K, 49.5K, 58.7K, and 64.4K proteins are the major outer membrane immunogens of P. multocida in rabbits. Lung lavages of immunized rabbits also contained similar antibody activities directed against several outer membrane proteins, with major activities against the 37.5K and 64.4K proteins.

Protective efficacy of monoclonal antibodies to class 1 and class 3 outer membrane proteins of Neisseria meningitidis B:15:P1.16 in infant rat infection model: new prospects for vaccine development

The protective efficacy of monoclonal antibodies to class 1 and class 3 outer membrane proteins of Neisseria meningitidis B:15:P1.16 was tested in an infant rat infection model. Four monoclonal antibodies to class 1 protein had bactericidal titres exceeding 20,000 and they protected infant rats completely against bacterial challenge with meningococci carrying the same class 1 protein, P1.16. One monoclonal antibody to class 3 protein was highly bactericidal (titer greater than 20,000), whereas two others had no bactericidal activity. All these antibodies gave some protection from infection, resulting in mortalities varying from 66 to 83% as compared to 100% in control rats who had received either unrelated monoclonal antibody or saline. These results strongly speak for class 1 outer membrane protein as a vaccine candidate for meningococcus group B.

Antibody response in group B meningococcal disease determined by enzyme-linked immunosorbent assay with serotype 15 outer membrane antigen

To elucidate pathogenic aspects and serodiagnostic possibilities for meningococcal disease, we investigated levels of specific antimeningococcal immunoglobulin G (IgG), IgA, and IgM in serum by using an enzyme-linked immunosorbent assay with outer membrane antigen prepared from a Neisseria meningitidis B:15:P1.16 strain. Serum samples were drawn on hospital admission as well as during convalescence from patients suspected of purulent meningitis or meningococcal septicemia, and single samples were drawn from population controls. A total of 637 samples were examined blindly. On admission, the average antimeningococcal immunoglobulin levels were about the same in the meningococcal disease patients as in the population controls. Septicemic patients, however, had significantly lower values. During one week the mean specific immunoglobulin levels in meningococcal-disease patients increased 6 times for IgG, 14 times for IgA, and 5 times for IgM. Children younger than 1 year showed a modest and more slowly developing antibody response. There were no statistically significant differences in average antibody responses among patients infected with meningococci of different serotypes. At 100% specificity, the increase in IgG, IgA, and IgM yielded diagnostic sensitivities for meningococcal disease of 84, 52, and 66%, respectively. One of seven serum pairs from the patient control group with unknown etiology was positive for meningococcal disease in this assay. The patients with meningococcal disease originally diagnosed only by clinical signs and symptoms showed a slightly lower rate of seroconversion than the patients in whom the diagnosis was supported by test results showing a systemic Neisseria meningitidis isolate.

Escherichia coli K51 and K93 capsular polysaccharides are crossreactive with the group A capsular polysaccharide of Neisseria meningitidis. Immunochemical, biological, and epidemiological studies

Eleven Escherichia coli strains, crossreactive with the capsular polysaccharide (CPS) of Neisseria meningitidis group A (GrA), were detected among 645 stool isolates from healthy families in Cairo, Egypt. 10 of these strains were of the O107:K93:H27 or O107:K93:SP serotypes and may be considered descendents of a single bacterium or as a clone. The remaining crossreactive strain was of the O7:K51:H18 serotype. None of the 11 strains produced enterotoxins and none were enteroinvasive. The purified CPS of these E. coli strains, as well as a polysaccharide (PS) from B. pumilis, strain Sh17, precipitated with equine GrA (H49) antiserum. A partial identity between the E. coli K93, K51 and Sh17 PS on the one hand and the GrA CPS on the other was observed by double immunodiffusion when reacted against the H49 antiserum. Four K93 strains and one K51 strain were found among 320 E. coli strains from patients at the Clinical Center, National Institutes of Health, and three K93 strains were found in 105 stool samples from children in Copenhagen. The data from these three surveys suggest that these crossreactive E. coli are common organisms and could serve as a stimulus for "natural" GrA CPS antibodies. Quantitative precipitation analysis showed that K51, K93, and Sh17 PS precipitated 25, 46.8, and 50% of H49 antibodies, respectively. Absorption of H49 antiserum with the GrA CPS removed its precipitating activity with the E. coli K93, K51, and Sh17 PS. Absorption of H49 antiserum with either K51 CPS or Sh17 PS removed the homologous crossreactivity only, whereas K93 CPS absorbed both K93 and K51 reactivities. Antibodies, raised by intravenous injection of formalinized E. coli K93 or K51 cells into rabbits, precipitated with GrA CPS and were bactericidal against GrA meningococci. The crossreaction between the E. coli K93 and the GrA CPS was unexpected since these two CPS are compositionally so dissimilar.

Human opsonins to meningococci after vaccination

Two groups of volunteers were immunized with either a serogroup A plus C meningococcal polysaccharide vaccine or a combined serogroup B polysaccharide-serotype 2 protein vaccine. Serum opsonin responses were measured by chemiluminescence of polymorphonuclear leukocytes exposed to opsonized live meningococci. Two of the six volunteers immunized with the A plus C vaccine had an increase in serum opsonins to group A meningococci, four responded to group C meningococci, and none to group B meningococci. Five other volunteers who were immunized with the combined group B polysaccharide-serotype 2 protein vaccine responded with an increase in serum opsonins to group B meningococci of two different protein serotypes, as well as to a group C-serotype 2 meningococcal strain. Although no booster effect was observed after a second dose of the combined vaccine, both the polysaccharide and the protein components appear to be able to stimulate an opsonin response.

Development of a Neisseria meningitidis group B serotype 2b protein vaccine and evaluation in a mouse model

Although serotype 2 remains the predominant cause of group B Neisseria meningitidis disease in many parts of the world, most cases of this disease are now due to serotype 2b rather than 2a. For this reason, we adapted the serotype 2a vaccine method of C. E. Frasch and M. S. Peppler (Infect. Immun. 37:271-280, 1982) to the production of a serotype 2b protein vaccine. A spontaneously occurring nonencapsulated mutant of the group B serotype 2b strain 3006 was obtained by selection on group B antiserum agar. Serotype 2b outer membrane protein vaccines were prepared with less than 1% lipoplysaccharide contamination. The immunogenicity of these vaccines was evaluated in mice in the presence and absence of meningococcal group B and group C capsular polysaccharides. The group B and group C polysaccharides equally potentiated the antibody response to the serotype 2b protein. Addition of aluminum hydroxide or aluminum phosphate markedly improved the antibody response to the serotype 2b protein, but aluminum hydroxide-adjuvanted vaccines consistently elicited higher antibody levels. Aluminum hydroxide-adsorbed serotype 2a and 2b protein vaccines were evaluated for induction of cross-protective bactericidal antibodies. The 2a vaccines were 2a specific, whereas the 2b vaccines elicited antibodies strongly bactericidal for both 2a and 2b meningococcal strains and protected against bacteremia in a mouse model. It may therefore be possible to provide protection against both 2a and 2b disease by using an aluminum hydroxide-adsorbed protein vaccine containing a single serotype 2 protein component.

Activation of murine B lymphocytes by Neisseria meningitidis and isolated meningococcal surface antigens

Heat-killed Neisseria meningitidis was found to be a potent mitogen for mouse splenic lymphocytes. Results obtained with different cell separation techniques indicated that the bacteria acted to selectively induce proliferation of B lymphocytes. First, partial or total depletion of T lymphocytes by treatment with various anti-T-cell antisera plus complement did not affect the ability of the remaining spleen cells to proliferate in response to N. meningitidis. Second, T lymphocytes purified by affinity chromatography through an immunoglobulin-antiimmunoglobulin-coated glass bead column were unresponsive to meningococcal stimulation, even when provided with a source of macrophages (irradiated or mitomycin C-treated spleen cells). Finally, treatment of spleen cells with soy bean agglutinin showed that, whereas the soy bean agglutinin-positive population (B-enriched lymphocytes) was highly responsive to stimulation by N. meningitidis, the soy bean agglutinin-negative population (T-enriched lymphocytes) displayed only a background level of proliferation when exposed to the bacteria. Isolated meningococcal surface antigens such as lipopolysaccharide (LPS) and outer membranes also possessed mitogenic activity and induced proliferation of B lymphocytes in a dose-dependent manner. Both LPS and non-LPS components contributed to the mitogenicity of outer membranes since the addition of outer membrane preparations to spleen cells from the low LPS responder C3H/HeJ mouse strain gave rise to a high level of proliferative activity.

Spin membrane immunoassay for use in meningococcal serology

A modified and improved spin membrane immunoassay has been developed for detecting complement-activating antibodies to Neisseria meningitidis capsular polysaccharide antigens. The polysaccharides were incorporated in the membranes of large unilamellar vesicles prepared by the reverse-phase evaporation method and filled with the water-soluble spin label tempocholine chloride. Upon addition of group-specific antisera and complement, the lipid membrane was damaged and the spin label leaked out. This process was monitored by electron spin resonance spectroscopy. A satisfactory assay was developed for polysaccharides of group A and C, whereas in the case of the B system the assay was more labile. The method is rapid and has a sensitivity comparable to that of radioimmunoassay. When studying paired sera from five recruits vaccinated with an A + C polysaccharide vaccine, significant rises in titers to both A and C polysaccharides were observed in all the postvaccination sera.

Preparation and physicochemical and immunological characterization of polysaccharide-outer membrane protein complexes of Neisseria meningitidis

A crude complex containing group C polysaccharide, outer membrane proteins, and lipopolysaccharide (LPS) was isolated from the cell-free culture liquid of Neisseria meningitidis serogroup C, serotype 2a. Group C polysaccharide and LPS were removed from this complex, resulting in an outer membrane complex and a purified complex, respectively. Analysis by electron microscopy showed the outer membrane origin of the crude complex and the outer membrane complex, whereas such a structure was absent in the purified complex. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis patterns of the three complexes were identical. Pyrolysis-mass spectrometry data correlated well with those obtained by the biochemical assays and suggested a low LPS content in the purified complex and a low polysaccharide content in the outer membrane complex. The purified complex was shown to be nonpyrogenic and could be prepared with the same yield as that of purified polysaccharide. The immunogenic activities of the complexes were studied in mice. The antibodies were measured by the enzyme-linked immunosorbent assay; and the bactericidal antibody assay. All complexes induced immunoglobulin G antibodies to group C polysaccharide as well as to the serotype antigen, although the removal of polysaccharide and LPS resulted in a reduction of the immunogenic activities of outer membrane complex and purified complex, respectively. A second dose of all complexes produced a clear booster effect of both antibody responses. The antibodies were bactericidal.

Antibody response of infants to cell surface-exposed outer membrane proteins of Haemophilus influenzae type b after systemic Haemophilus disease

The immune response of nine infants with Haemophilus influenzae type b meningitis was examined by using a radioimmunoprecipitation procedure designed to detect antibodies directed against cell surface-exposed outer membrane proteins of this pathogen. Using intrinsically or extrinsically radiolabeled intact H. influenzae type b cells with acute- and convalescent-phase human sera in this radioimmunoprecipitation system, we found that all of the infants produced an antibody response directed against several different H. influenzae type b outer membrane proteins. Anti-H. influenzae type b outer membrane protein antibodies present in convalescent sera, but not found in acute sera, were directed against cell surface-exposed H. influenzae type b outer membrane proteins. In contrast, both acute and convalescent sera contained antibody activity directed against numerous H. influenzae type b outer membrane proteins whose antigenic determinants were apparently inaccessible to antibody on intact H. influenzae type b cells. The ability of infants to develop an antibody response to cell surface-exposed, antibody-accessible H. influenzae type b outer membrane proteins indicates that these proteins may have vaccinogenic potential.

Protection against group B Neisseria meningitidis disease: preparation of soluble protein and protein-polysaccharide immunogens

Although effective polysaccharide vaccines have been developed for meningococcal groups A, C, Y, and W135, the purified group B polysaccharide has proven to be nonimmunogenic. Earlier studies indicated that serotype 2 outer membrane protein vaccines induced bactericidal antibodies in animals and protected them from meningococcal challenge. However, a similar vaccine induced only low levels of antiprotein antibodies in both adults and children (C.E. Frasch et al., in J.B. Robbins et al., ed., Seminars in Infectious Disease vol. 4, p. 263-267, 1982). Methods were therefore developed to produce more immunogenic serotype 2 protein vaccines. We found that, by growing the organism for 65 to 72 h at 32 degrees C, three to four times more outer membrane protein was released into the culture medium than could be extracted from overnight-grown cells. The outer membranes were therefore purified directly from the broth by ultrafiltration followed by ammonium sulfate precipitation. Most of the lipopolysaccharide was selectively removed from the membranes by treatment with the nonionic detergent Brij-96. The Brij-96 was then removed and the resulting vaccine was filter sterilized. Some vaccines were prepared by combining equal parts of detergent-treated membrane protein and high-molecular-weight group B polysaccharide producing highly soluble vaccines. These new vaccines were compared by using an enzyme-linked immunosorbent inhibition assay to an insoluble vaccine (E-06) found to be poorly immunogenic in humans. A human serum with serotype 2 specificity was used in the inhibition assay, and 5 microgram of E-06 was required for 50% inhibition, whereas less than 1 microgram of the soluble vaccines was required. Addition of group B polysaccharide slightly increased the inhibitory capacity of the protein component.

Natural bactericidal activity of human serum against Neisseria meningitidis isolates of different serogroups and serotypes

We used a microtiter assay, standardized with serum-sensitive and serum-resistant strains of Neisseria gonorrhoeae, to determine the serum sensitivity of Neisseria meningitidis isolates of different serogroups and serotypes. Numbers of serum-resistant isolates varied among serogroups: group A = 7/8 (88%), group B = 26/50 (52%), group C = 5/8 (63%), group Y = 4/6 (67%), group W135 = 5/8 (63%), group 29E (Z') = 0/8 (0%), nongroupable isolates = 0/8 (0%). In comparison to group B isolates, group A isolates were more serum resistant (P less than 0.06), and group 29E and nongroupable isolates were more serum sensitive (P less than 0.001). Poor correlation was observed between serum sensitivity results and group-specific levels of bactericidal antibody in the normal human serum of volunteers. The frequency of serum-resistant strains among group B disease isolates (45%) was not significantly different from throat isolates of asymptomatic carriers (52%). Serotype 2 isolates of group B were no more serum resistant than were other serotypes examined. The serum sensitivity of meningococci appears to involve both capsular and noncapsular antigens and varies between serogroups. The increased serum sensitivity of nongroupable and group 29E isolates may account for the low incidence of disease caused by these organisms.

Protection against group B Neisseria meningitidis disease: effect of serogroup B polysaccharide and polymyxin B on immunogenicity of serotype protein preparations

The inability to prepare an effective polysaccharide vaccine against group B Neisseria meningitidis was the impetus for these studies. Outer membrane protein vaccines used in our initial studies failed to induce bactericidal antibodies in humans. The particulate nature of these vaccines may have led to their clearance before effective immune stimulation. Less denaturing procedures, therefore, were developed for preparation of serotype 2 protein-containing vaccines. These procedures included isolation of naturally released outer membrane vesicles and selective removal of lipopolysaccharide from the vesicles by the nonionic detergent Brij-96. The resultant protein vaccines were evaluated with and without noncovalently complexed group B meningococcal polysaccharide or polymyxin B sulfate or both. The new vaccines were at least 10-fold more immunogenic in mice and guinea pigs than the previous vaccines when assayed for bactericidal and enzyme-linked immunosorbent assay antibodies. The protein vaccines alone protected guinea pigs from intrachamber infection, and a single 0.1-microgram injection prevented meningococcal bacteremia in mice. Addition of group B polysaccharide to the protein significantly improved the immunogenicity of the protein, and this combined vaccine showed a greater protective effect. Polymyxin B generally reduced the immunogenicity of the vaccines in both mice and guinea pigs.

The meningococcus and mechanisms of pathogenicity

Images

Meningococcal disease in Scandinavia

Scandinavia (Denmark, Finland, Iceland, Norway, and Sweden) comprises with mutual borders and 22.3 million inhabitants an area where the socioeconomic and cultural conditions are similar. Epidemic diseases, such as meningococcal infection, might therefore be expected to be uniformly distributed. An epidemiological study in the 10-year period 1970-9 shows, however, remarkable differences in the incidence, age, and serogroup and type distribution, as well as in the general dynamics of the disease. Three epidemics, two caused by different serotypes of group B (Norway and Iceland) and one by group A (Finland) occurred within the observation period. The annual overall incidence was generally around 3/100 000 but increased from fivefold (Finland) to eightfold (northern Norway) during epidemics. The epidemic strains caused infection in over 3000 patients and the loss of at least 250 lives. The overall case fatality rate was 8.6% (range 4.1-13.7%). Men were more susceptible and had a worse prognosis than women of the same age group. The group A epidemic in Finland was influenced by a large vaccination campaign, but this possibility was not feasible in the two other epidemics.

Monoclonal antibodies directed against a cell surface-exposed outer membrane protein of Haemophilus influenzae type b

Monoclonal antibodies directed against several different Haemophilus influenzae type b outer membrane proteins with apparent molecular weights of 45,000, 39,000, and 37,000 were identified by a radioimmunoprecipitation method. Five monoclonal antibodies, including both immunoglobulin G and M isotypes, were specific for the same H. influenzae type b major outer membrane protein (39,000 molecular weight). One of these immunoglobulin G monoclonal antibodies (6A2) was shown to be directed against a cell surface-exposed antigenic determinant of the 39,000-molecular-weight protein, whereas the other monoclonal antibodies directed against this same protein were apparently specific for antigenic determinants not exposed on the H. Influenzae type b cell surface. The cell surface-exposed protein antigenic determinant recognized by monoclonal antibody 6A2 was not unique to the H. influenzae type b strain used as the source of outer membrane vesicles for generating immune spleen cells, but was found in a majority of independently isolated strains of H. influenzae type b. These data indicate that there is antigenic cross-reactivity among H. influenzae type b strains with regard to cell surface-exposed proteins.