Measurement of antibodies against meningococcal capsular polysaccharides B and C in enzyme-linked immunosorbent assays: towards an improved surveillance of meningococcal disease

Induction of Susceptibility to Disseminated Infection with IgA1 Protease-Producing Encapsulated Pathogens Streptococcus pneumoniae, Haemophilus influenzae Type b, and Neisseria meningitidis

Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae are the principal causes of bacterial meningitis. It is unexplained why only occasional individuals develop invasive infection, while the vast majority remain healthy and develop immunity when encountering these pathogens. A capsular polysaccharide and an IgA1 protease are common to these pathogens. We tested the hypothesis that patients are primed to susceptibility to invasive infection by other bacteria that express the same capsular polysaccharide but no IgA1 protease. Thereby, the subsequently colonizing pathogen may protect its surface with IgA1 protease-generated Fab fragments of IgA1 devoid of Fc-mediated effector functions. Military recruits who remained healthy when acquiring meningococci showed a significant response of inhibitory antibodies against the IgA1 protease of the colonizing clone concurrent with serum antibodies against its capsular polysaccharide. At hospitalization, 70.8% of meningitis patients carried fecal bacteria cross-reactive with the capsule of the actual pathogen, in contrast to 6% of controls (P < 0.0001). These were Escherichia coli K100, K1, and K92 in patients with infection caused by H. influenzae type b and N. meningitidis groups B and C, respectively. This concurred with a significant IgA1 response to the capsule but not to the IgA1 protease of the pathogen. The demonstrated multitude of relationships between capsular types and distinct IgA1 proteases in pneumococci suggests an alternative route of immunological priming associated with recombining bacteria. The findings support the model and offer an explanation for the rare occurrence of invasive diseases in spite of the comprehensive occurrence of the pathogens.

Specificity of the immune response to a modified group B meningococcal polysaccharide conjugate vaccine

Antibodies to a modified group B meningococcal polysaccharide vaccine were examined for antigenic and functional specificities. Bactericidal determinants were investigated by using immunoaffinity columns and competitive inhibition of bactericidal activity in an in vitro killing assay. We conclude that nearly all of the vaccine-induced bactericidal activity is specific for the native polysaccharide.

Development and evaluation of a rapid multianalyte particle-based flow cytometric assay for the quantification of meningococcal serogroup B-specific IgM antibodies in sera for nonculture case confirmation

Serogroup-specific antibody has been shown to be present in the sera of patients recovering from meningococcal disease, and thus the detection of such antibodies may aid in the confirmation of disease. There are currently no standard methods for measuring meningococcal serogroup B-specific antibody in sera. Here, we report the development of a microsphere-based immunoassay which utilizes colominic acid from Escherichia coli 07:K1 (L):NM to detect immunoglobulin M directed against serogroup B polysaccharide. The serogroup B assay was incorporated into a multiplex assay which also detects serogroup-specific immunoglobulin M for meningococcal serogroups A, C, Y and W-135. Using the method of cross-standardization, serogroup B-specific immunoglobulin M concentrations were assigned to the standard serum CDC 1992. The assay is able to detect increases in specific immunoglobulin M concentrations from acute to convalescent phase serum from serogroup B cases, and can be utilized in conjunction with the previously developed tetraplex immunoglobulin G detection assay for serogroups A, C, Y and W-135.

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.

Protection by natural human immunoglobulin M antibody to meningococcal serogroup B capsular polysaccharide in the infant rat protection assay is independent of complement-mediated bacterial lysis

Neisseria meningitidis, an important cause of bacterial meningitis and septicemia worldwide, is associated with high mortality and serious sequelae. Natural immunity against meningococcal disease develops with age, but the specificity and functional activity of natural antibodies associated with protection are poorly understood. We addressed this question by using a selected subset of prevaccination sera (n = 26) with convergent or discrepant serum bactericidal activity (SBA) and infant rat protective activity (IRPA) against the serogroup B meningococcal strain 44/76-SL (B:15:P1.7,16) from Icelandic teenagers. The sera were analyzed by opsonophagocytic activity (OPA) assay, immunoblotting, immunoglobulin G (IgG) quantitation against live meningococcal cells by flow cytometry, and enzyme immunosorbent assay (EIA). High levels of SBA and OPA were reflected in distinct IgG binding to major outer membrane proteins and/or lipopolysaccharide in immunoblots. However, we could not detect any specific antibody patterns on blots that could explain IRPA. Only IgM antibody to group B capsular polysaccharide (B-PS), measured by EIA, correlated positively (r = 0.76, P < 0.001) with IRPA. Normal human sera (NHS; n = 20) from healthy Finnish children of different ages (7, 14, and 24 months and 10 years) supported this finding and showed an age-related increase in IRPA that coincided with the acquisition of B-PS specific IgM antibody. The protection was independent of complement-mediated bacterial lysis, as detected by the inability of NHS to augment SBA in the presence of human or infant rat complement and the equal protective activity of NHS in rat strains with fully functional or C6-deficient complement.

Diagnostic assessment of haemorrhagic rash and fever

AIMS

To establish criteria for early distinction between meningococcal disease and other conditions with similar clinical features, and to identify other causes for haemorrhagic rashes accompanied by fever.

METHODS

In a prospective study, 264 infants and children hospitalised with fever and skin haemorrhages were studied.

RESULTS

We identified an aetiological agent in 28%: 15% had meningococcal disease, 2% another invasive bacterial infection, 7% enterovirus infection, and 4% adenovirus infection. Five clinical variables distinguished between meningococcal disease and other conditions on admission: (1) skin haemorrhages of characteristic appearance; (2) universal distribution of skin haemorrhages; (3) maximum diameter of one or more skin haemorrhages greater than 2 mm; (4) poor general condition (using a standardised observation scheme); and (5) nuchal rigidity. If any two or more of these clinical variables were present, the probability of identifying a patient with meningococcal disease was 97% and the false positive rate was only 12%. This diagnostic algorithm did not identify children in whom septicaemia was caused by other bacterial species.

P64k meningococcal protein as immunological carrier for weak immunogens

Previously, the P64k meningococcal protein, an antigen of 64 kDa expressed in Escherichia coli, has been extensively characterized. We have successfully conjugated several synthetic peptides and meningococcal group C polysaccharide to P64k. In three out of four model peptides, the murine humoral immune response against the homologous peptide, evaluated after three doses of conjugate, was higher in the animals immunized with the coupled peptide than in those that received free peptide. The fourth and largest was immunogenic by itself. Similarly, the antigroup C polysaccharide levels reached by conjugated polysaccharide were significantly higher than those produced against unconjugated polysaccharide. As a carrier for one of the peptides, P64k was compared with bovine serum albumin (BSA) and tetanus toxoid (TT), being able to induce slightly higher or similar antipeptide antibody levels than these well-establish protein carriers. Our results suggest that recombinant P64k protein could be a readily available immunological carrier, as efficient as other commonly used large carrier molecules.