Antigenic relationships among immunoglobulin A1 proteases from Haemophilus, Neisseria, and Streptococcus species

Neisseria gonorrhoeae vaccines: a contemporary overview

Neisseria gonorrhoeae infection is an important public health issue, with an annual global incidence of 87 million. N. gonorrhoeae infection causes significant morbidity and can have serious long-term impacts on reproductive and neonatal health and may rarely cause life-threatening disease. Global rates of N. gonorrhoeae infection have increased over the past 20 years. Importantly, rates of antimicrobial resistance to key antimicrobials also continue to increase, with the United States Centers for Disease Control and Prevention identifying drug-resistant N. gonorrhoeae as an urgent threat to public health. This review summarizes the current evidence for N. gonorrhoeae vaccines, including historical clinical trials, key N. gonorrhoeae vaccine preclinical studies, and studies of the impact of Neisseria meningitidis vaccines on N. gonorrhoeae infection. A comprehensive survey of potential vaccine antigens, including those identified through traditional vaccine immunogenicity approaches, as well as those identified using more contemporary reverse vaccinology approaches, are also described. Finally, the potential epidemiological impacts of a N. gonorrhoeae vaccine and research priorities for further vaccine development are described.

IgA1 Protease as a Vaccine Basis for Prevention of Bacterial Meningitis

Abstract

The review covers the study of the protective properties of IgA1 protease and the possibility of creating a vaccine preparation for the prevention of bacterial meningitis of various origins on its basis. Bacterial meningitis belongs to the group of socially dangerous diseases and is characterized by a severe course, numerous complications and high mortality. The approaches used at present in world practice to create antimicrobial vaccines are based on a narrow targeting against a specific pathogen. The development of a monocomponent vaccine against a wide range of bacterial pathogens with a common virulence factor is still relevant. IgA1 protease, a protein that is one of the main virulence factors of a number of gram-negative and gram-positive bacteria, can serve as such an antigen. Bacterial IgA1 protease is uniquely specific for immunoglobulins A1 (IgA1), cleaving peptide bonds in the hinge regions of the IgA1 in humans and other higher primates. Bacteria, getting on the mucous membrane, destroy IgA1, which acts as the first barrier to protect the body from infections. Neutralization of IgA1 protease at this stage can become an obstacle to the development of infection, hindering the adhesion of a number of pathogens that produce this protein. The data available in the literature on the mechanism of antibacterial protection are scattered and ambiguous. The review considers the literature data and the results of our own experiments on the protective activity of IgA1 protease. We have shown that the recombinant meningococcal IgA1 protease and some of its fragments protect mice from infection with a live virulent culture not only of meningococci of the main epidemic serogroups (A, B, C, and W135), but also of some of the most common virulent pneumococcal serotypes. The data obtained indicate the possibility of creating a monocomponent vaccine against these and, possibly, other bacterial infections. Currently, significant progress has been made in studying the structure and functions of secreted proteins in the bacteria Neisseria meningitidis and Haemophilus influenzae. In this review we describe protein translocation systems of N. meningitidis, which are related to the secretion of proteins in these bacteria, and also present modern data on the functions of these proteins. Analysis of experimental data on the structure of IgA1 protease of N. meningitidis and the formation of immunity during vaccination is of key importance in the development of prophylactic preparations.

Immunoglobulin A Glycosylation and Its Role in Disease

Human IgA is comprised of two subclasses, IgA1 and IgA2. Monomeric IgA (mIgA), polymeric IgA (pIgA), and secretory IgA (SIgA) are the main molecular forms of IgA. The production of IgA rivals all other immunoglobulin isotypes. The large quantities of IgA reflect the fundamental roles it plays in immune defense, protecting vulnerable mucosal surfaces against invading pathogens. SIgA dominates mucosal surfaces, whereas IgA in circulation is predominately monomeric. All forms of IgA are glycosylated, and the glycans significantly influence its various roles, including antigen binding and the antibody effector functions, mediated by the Fab and Fc portions, respectively. In contrast to its protective role, the aberrant glycosylation of IgA1 has been implicated in the pathogenesis of autoimmune diseases, such as IgA nephropathy (IgAN) and IgA vasculitis with nephritis (IgAVN). Furthermore, detailed characterization of IgA glycosylation, including its diverse range of heterogeneity, is of emerging interest. We provide an overview of the glycosylation observed for each subclass and molecular form of IgA as well as the range of heterogeneity for each site of glycosylation. In many ways, the role of IgA glycosylation is in its early stages of being elucidated. This chapter provides an overview of the current knowledge and research directions.

Protective potency of recombinant meningococcal IgA1 protease and its structural derivatives upon animal invasion with meningococcal and pneumococcal infections

Immunization of mice with recombinant IgA1 protease of Neisseria meningitidis or several structural derivatives thereof protects the animals infected with a variety of deadly pathogens, including N. meningitidis serogroups A, B, and C and 3 serotypes of Streptococcus pneumonia. In sera of rabbits immunized with inactivated pneumococcal cultures, antibodies binding IgA1-protease from N. meningitidis serogroup B were detected. Thus, the cross-reactive protection against meningococcal and pneumococcal infections has been demonstrated in vivo. Presumably it indicates the presence of common epitopes in the N. meningitidis IgA1 protease and S. pneumoniae surface proteins.

Occurrence and evolution of the paralogous zinc metalloproteases IgA1 protease, ZmpB, ZmpC, and ZmpD in Streptococcus pneumoniae and related commensal species

The distribution, genome location, and evolution of the four paralogous zinc metalloproteases, IgA1 protease, ZmpB, ZmpC, and ZmpD, in Streptococcus pneumoniae and related commensal species were studied by in silico analysis of whole genomes and by activity screening of 154 representatives of 20 species. ZmpB was ubiquitous in the Mitis and Salivarius groups of the genus Streptococcus and in the genera Gemella and Granulicatella, with the exception of a fragmented gene in Streptococcus thermophilus, the only species with a nonhuman habitat. IgA1 protease activity was observed in all members of S. pneumoniae, S. pseudopneumoniae, S. oralis, S. sanguinis, and Gemella haemolysans, was variably present in S. mitis and S. infantis, and absent in S. gordonii, S. parasanguinis, S. cristatus, S. oligofermentans, S. australis, S. peroris, and S. suis. Phylogenetic analysis of 297 zmp sequences and representative housekeeping genes provided evidence for an unprecedented selection for genetic diversification of the iga, zmpB, and zmpD genes in S. pneumoniae and evidence of very frequent intraspecies transfer of entire genes and combination of genes. Presumably due to their adaptation to a commensal lifestyle, largely unaffected by adaptive mucosal immune factors, the corresponding genes in commensal streptococci have remained conserved. The widespread distribution and significant sequence diversity indicate an ancient origin of the zinc metalloproteases predating the emergence of the humanoid species. zmpB, which appears to be the ancestral gene, subsequently duplicated and successfully diversified into distinct functions, is likely to serve an important but yet unknown housekeeping function associated with the human host.

The paralogous zinc metalloproteases IgA1 protease, ZmpB, ZmpC, and ZmpD have been identified as crucial for virulence of the human pathogen Streptococcus pneumoniae. This study maps the presence of the corresponding genes and enzyme activities in S. pneumoniae and in related commensal species of the genera Streptococcus, Gemella, and Granulicatella. The distribution, genome location, and sequence diversification indicate that zmpB is the ancestral gene predating the evolution of today’s humanoid species. The ZmpB protease may play an important but yet unidentified role in the association of streptococci of the Mitis and Salivarius groups with their human host, as it is ubiquitous in these two groups, except for a fragmented gene in Streptococcus thermophilus, the only species not associated with humans. The relative sequence diversification of the IgA1 protease, ZmpB, and ZmpD is striking evidence of differences in selection for diversification of these surface-exposed proteins in the pathogen S. pneumoniae compared to the closely related commensal streptococci.

Characterization of igaB, a second immunoglobulin A1 protease gene in nontypeable Haemophilus influenzae

Nontypeable Haemophilus influenzae is an important respiratory pathogen, causing otitis media in children and lower respiratory tract infection in adults with chronic obstructive pulmonary disease (COPD). Immunoglobulin A1 (IgA1) protease is a well-described protein and potential virulence factor in this organism as well as other respiratory pathogens. IgA1 proteases cleave human IgA1, are involved in invasion, and display immunomodulatory effects. We have identified a second IgA1 protease gene, igaB, in H. influenzae that is present in addition to the previously described IgA1 protease gene, iga. Reverse transcriptase PCR and IgA1 protease assays indicated that the gene is transcribed, expressed, and enzymatically active in H. influenzae. The product of this gene is a type 2 IgA1 protease with homology to the iga gene of Neisseria species. Mutants that were deficient in iga, igaB, and both genes were constructed in H. influenzae strain 11P6H, a strain isolated from a patient with COPD who was experiencing an exacerbation. Analysis of these mutants indicated that igaB is the primary mediator of IgA1 protease activity in this strain. IgA1 protease activity assays on 20 clinical isolates indicated that the igaB gene is associated with increased levels of IgA1 protease activity. Approximately one-third of 297 strains of H. influenzae of diverse clinical and geographic origin contained igaB. Significant differences in the prevalence of igaB were observed among isolates from different sites of isolation (sputum > middle ear > nasopharynx). These data support the hypothesis that the newly discovered igaB gene is a potential virulence factor in nontypeable H. influenzae.

Neisserial immunoglobulin A1 protease induces specific T-cell responses in humans

We have previously shown that immunoglobulin A1 (IgA1) protease, an exoenzyme of pathogenic neisseriae, can trigger the release of proinflammatory cytokines from human monocytic subpopulations. Here, we demonstrate a dose-dependent T-cell response to recombinant gonococcal IgA1 protease (strain MS11) in healthy human blood donors. This response was delayed in comparison to the immune response against tetanus toxoid. Stimulation with IgA1 protease led to the activation of CD4(+) and CD8(+) T cells, as well as CD19(+) B cells and CD56(+) NK cells, indicated by de novo expression of CD69. Only CD4(+) T cells proliferated and stained positive for intracellular gamma interferon (IFN-gamma). Both proliferation and IFN-gamma production were dependent on antigen presentation via major histocompatibility complex class II. Peripheral blood mononuclear cells stimulated with IgA1 protease produce IFN-gamma and tumor necrosis factor alpha but no, or very low amounts of, interleukin-10 (IL-10) or IL-4, indicating a Th1-based proinflammatory immune response. These findings support the significance of IgA1 protease as a virulence determinant of bacterial meningitis and its function as a dominant proinflammatory T-cell antigen.

Identification and characterization of an in vivo regulated D15/Oma87 homologue in Shigella flexneri using differential display polymerase chain reaction

Shigella genes expressed during infection likely contribute to adaptation and virulence in the host. Using differential display PCR (DDPCR), a cDNA fragment from Shigella flexneri serotype 5 that showed enhanced expression in a murine model was identified, cloned and sequenced. Enhanced expression was verified by RNA dot blot. The full-length gene was cloned using PCR and sequenced. The complete gene sequence was BLAST searched against GenBank, and exhibited strong homology to genes encoding Haemophilus influenzae D15 and Pasteurella multocida Oma87 protective outer membrane antigens. The S. flexneri gene putatively encodes a approximately 90-kDa protein and was termed oma90. The deduced amino acid sequence from oma90 was analyzed and compared to the D15/Oma87 antigens. Additionally, oma90 mapped to a cluster of orthologous groups, and probably contains an ancient conserved domain. The chromosomal organization of oma90 was similar to that for H. influenzae and P. multocida as well as for other known homologues. Northern blot revealed that the oma90 transcript encoded only oma90. This report represents the first description of a S. flexneri gene identified based on enhanced expression in the host. Furthermore, we report the first evidence demonstrating in vivo regulation of a member of the d15/oma87 gene family.

Evaluation of immunoglobulin A1 (IgA1) protease and IgA1 protease-inhibitory activity in human female genital infection with Neisseria gonorrhoeae

Immunoglobulin A1 (IgA1) protease, an enzyme that selectively cleaves human IgA1, may be a virulence factor for pathogenic organisms such as Neisseria gonorrhoeae. Host protection from the effects of IgA1 protease includes antibody-mediated inhibition of IgA1 protease activity, and it is believed that the relative balance between IgA1 protease and inhibitory antibodies contributes to the pathogenesis of disease caused by IgA1 protease-producing organisms. We have examined the levels of these two opposing factors in genital tract secretions and sera from women with uncomplicated infection with N. gonorrhoeae. When IgA1 in cervical mucus was examined by Western blotting, no evidence of cleavage fragments characteristic of IgA1 protease activity was seen in gonococcus-infected or control patients. Cleavage fragments typical of IgA1 protease were detected, however, after the addition of exogenous IgA1 protease to cervical mucus. Degraded IgA1 was detected in some vaginal wash samples, but the fragment pattern was not typical of IgA1 protease activity. All N. gonorrhoeae isolates from the infected patients produced IgA1 protease in vitro. All but two serum samples and 16 of 65 cervical mucus samples displayed inhibitory activity against gonococcal IgA1 protease, but there was no significant difference in the level of inhibitory activity between gonococcus-infected and noninfected patients in either cervical mucus or serum. There was no difference in the levels of IgA1 protease-inhibitory activity in serum or cervical mucus collected from patients at recruitment and 2 weeks later. These results suggest that cleavage of IgA1 by gonococcal IgA1 protease within the lumen of the female lower genital tract is unlikely to be a significant factor in the pathogenesis of infections by N. gonorrhoeae.

A comprehensive genetic study of streptococcal immunoglobulin A1 proteases: evidence for recombination within and between species

An analysis of 13 immunoglobulin A1 (IgA1) protease genes (iga) of strains of Streptococcus pneumoniae, Streptococcus oralis, Streptococcus mitis, and Streptococcus sanguis was carried out to obtain information on the structure, polymorphism, and phylogeny of this specific protease, which enables bacteria to evade functions of the predominant Ig isotype on mucosal surfaces. The analysis included cloning and sequencing of iga genes from S. oralis and S. mitis biovar 1, sequencing of an additional seven iga genes from S. sanguis biovars 1 through 4, and restriction fragment length polymorphism (RFLP) analyses of iga genes of another 10 strains of S. mitis biovar 1 and 6 strains of S. oralis. All 13 genes sequenced had the potential of encoding proteins with molecular masses of approximately 200 kDa containing the sequence motif HEMTH and an E residue 20 amino acids downstream, which are characteristic of Zn metalloproteinases. In addition, all had a typical gram-positive cell wall anchor motif, LPNTG, which, in contrast to such motifs in other known streptococcal and staphylococcal proteins, was located in their N-terminal parts. Repeat structures showing variation in number and sequence were present in all strains and may be of relevance to the immunogenicities of the enzymes. Protease activities in cultures of the streptococcal strains were associated with species of different molecular masses ranging from 130 to 200 kDa, suggesting posttranslational processing possibly as a result of autoproteolysis at post-proline peptide bonds in the N-terminal parts of the molecules. Comparison of deduced amino acid sequences revealed a 94% similarity between S. oralis and S. mitis IgA1 proteases and a 75 to 79% similarity between IgA1 proteases of these species and those of S. pneumoniae and S. sanguis, respectively. Combined with the results of RFLP analyses using different iga gene fragments as probes, the results of nucleotide sequence comparisons provide evidence of horizontal transfer of iga gene sequences among individual strains of S. sanguis as well as among S. mitis and the two species S. pneumoniae and S. oralis. While iga genes of S. sanguis and S. oralis were highly homogeneous, the genes of S. pneumoniae and S. mitis showed extensive polymorphism reflected in different degrees of antigenic diversity.

Comparative analysis of immunoglobulin A1 protease activity among bacteria representing different genera, species, and strains

Immunoglobulin A1 (IgA1) proteases cleaving human IgA1 in the hinge region are produced constitutively by a number of pathogens, including Haemophilus influenzae, Neisseria meningitidis, Neisseria gonorrhoeae, and Streptococcus pneumoniae, as well as by some members of the resident oropharyngeal flora. Whereas IgA1 proteases have been shown to interfere with the functions of IgA antibodies in vitro, the exact role of these enzymes in the relationship of bacteria to a human host capable of responding with enzyme-neutralizing antibodies is not clear. Conceivably, the role of IgA1 proteases may depend on the quantity of IgA1 protease generated as well as on the balance between secreted and cell-associated forms of the enzyme. Therefore, we have compared levels of IgA1 protease activity in cultures of 38 bacterial strains representing different genera and species as well as strains of different pathogenic potential. Wide variation in activity generation rate was found overall and within some species. High activity was not an exclusive property of bacteria with documented pathogenicity. Almost all activity of H. influenzae, N. meningitidis, and N. gonorrhoeae strains was present in the supernatant. In contrast, large proportions of the activity in Streptococcus, Prevotella, and Capnocytophaga species was cell associated at early stationary phase, suggesting that the enzyme may play the role of a surface antigen. Partial release of cell-associated activity occurred during stationary phase. Within some taxa, the degree of activity variation correlated with degree of antigenic diversity of the enzyme as determined previously. This finding may indicate that the variation observed is of biological significance.

Characterization of the Streptococcus pneumoniae immunoglobulin A1 protease gene (iga) and its translation product

Bacterial immunoglobulin A1 (IgA1) proteases constitute a very heterogenous group of extracellular endopeptidases which specifically cleave human IgA1 in the hinge region. Here we report that the IgA1 protease gene, iga, of Streptococcus pneumoniae is homologous to that of Streptococcus sanguis. By using the S. sanguis iga gene as hybridization probe, the corresponding gene from a clinical isolate of S. pneumoniae was isolated in an Escherichia coli lambda phage library. A lysate of E. coli infected with hybridization-positive recombinant phages possessed IgA1-cleaving activity. The complete sequence of the S. pneumoniae iga gene was determined. An open reading frame with a strongly biased codon usage and having the potential of encoding a protein of 1,927 amino acids with a molecular mass of 215,023 Da was preceded by a potential -10 promoter sequence and a putative Shine-Dalgarno sequence. A putative signal peptide was found in the N-terminal end of the protein. The amino acid sequence similarity to the S. sanguis IgA1 protease indicated that the pneumococcal IgA1 protease is a Zn-metalloproteinase. The primary structures of the two streptococcal IgA1 proteases were quite different in the N-terminal parts, and both proteins contained repeat structures in this region. Using a novel assay for IgA1 protease activity upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis, we demonstrated that the secreted IgA1 protease was present in several different molecular forms ranging in size from approximately 135 to 220 kDa. In addition, interstrain differences in the sizes of the pneumococcal IgA1 proteases were detected. Southern blot analyses suggested that the S. pneumoniae iga gene is highly heterogenous within the species.

Extracellular proteinase activity of Cryptococcus neoformans

Extracellular proteinase activity was studied for eight strains of Cryptococcus neoformans var. neoformans and two strains of Cryptococcus neoformans var. gattii. Proteinase activity was measured by protein agar clearance, azoalbumin hydrolysis, gelatin liquefaction, and protein substrate polyacrylamide gel electrophoresis. All strains of C. neoformans produced extracellular proteolytic activity. Maximal extracellular proteinase activity in supernatants of C. neoformans cultures was associated with late logarithmic- and stationary-phase cultures. C. neoformans was able to utilize murine immunoglobulin G1, bovine immunoglobulin G, and human complement factor 5 for growth in media containing these proteins as the sole sources of carbon and nitrogen, suggesting a capacity to degrade immunologically important proteins. Protein substrate polyacrylamide gel electrophoresis revealed several bands with proteolytic activity at apparent molecular masses of 200, 100, and 50 kDa. The results confirm the existence of extracellular proteinase activity for C. neoformans.

A method for titration of inhibiting antibodies to bacterial immunoglobulin A1 proteases in human serum and secretions

Bacterial IgA1 proteases specifically cleave IgA1, including S-IgA1, molecules into Fab alpha and Fc alpha fragments. Hereby these enzymes interfere with the protective functions of antibodies belonging to this isotype. Antibodies inhibiting IgA1 proteases have been detected in humans, but the titration of such antibodies is a matter of methodological concern. Because human serum and secretions contain IgA1 substrate, it is impossible to provide uniform substrate conditions for samples of IgA1 protease incubated with inhibitors differing in their origin and state of dilution. This study demonstrates that such variations in substrate are not prohibitive for a reliable titration of inhibiting antibodies. This was evident from experiments demonstrating that the variations do not interfere with the quantification of residual IgA1 protease activity provided the activity is measured in terms of the proportion of IgA1 substrate cleaved during incubation. Proportions of cleaved IgA1 were measured by exploiting the differential reactivity of cleaved and intact IgA1 molecules in an ELISA using anti-Fc alpha and enzyme-conjugated anti-light chain antibodies for catching and development, respectively. A protocol for the titration of IgA1 protease-inhibiting antibodies based on this ELISA is described. By application of the protocol to chromatographic fractions of saliva, IgA1 protease-inhibiting activity was found to co-purify with salivary S-IgA.

Biological significance of IgA1 proteases in bacterial colonization and pathogenesis: critical evaluation of experimental evidence

IgA1 protease activity, which allows bacteria to cleave human IgA1 in the hinge region, represents a striking example of convergent evolution of a specific property in bacteria. Although it has been known since 1979 that IgA1 protease is produced by the three leading causes of bacterial meningitis in addition to important urogenital pathogens and some members of the oropharyngeal flora, the exact role of this enzyme in bacterial pathogenesis is still incompletely understood owing to lack of a satisfactory animal model. Cleavage of IgA1 by these post-proline endopeptidases efficiently separates the monomeric antigen-binding fragments from the secondary effector functions of the IgA1 antibody molecule. Several in vivo and in vitro observations indicate that the enzymes are important for the ability of bacteria to colonize mucosal membranes in the presence of S-IgA antibodies. Furthermore, the extensive cleavage of IgA sometimes observed in vivo, suggests that IgA1 protease activity results in a local functional IgA deficiency that may facilitate colonization of other microorganisms and the penetration of potential allergens. It has been hypothesized that IgA1 protease activity of Haemophilus influenzae, Neisseria meningitidis, and Streptococcus pneumoniae, under special immunological circumstances, allows these bacteria to take advantage of specific IgA1 antibodies in a strategy to evade other immune factors of the human body. The decisive factor is the balance between IgA antibodies against surface antigens of the respective bacteria and their IgA1 protease. Recent studies have shown that serine-type IgA1 proteases of H. influenzae, meningococci, and gonococci belong to a family of proteins used by a diverse group of Gram-negative bacteria for colonization and invasion.

Distinct antigenic and genetic properties of the immunoglobulin A1 protease produced by Haemophilus influenzae biogroup aegyptius associated with Brazilian purpuric fever in Brazil

All examined Haemophilus influenzae biogroup aegyptius isolates of the clone associated with Brazilian purpuric fever (the BPF clone) produced type 2 immunoglobulin A1 (IgA1) proteases encoded by identical iga genes that were distinct from the iga genes of other Brazilian H. influenzae biogroup aegyptius isolates. A partial nucleotide sequence analysis revealed close similarities to the iga genes of H. influenzae serotype c and one noncapsular H. influenzae biotype III strain isolated from a case of conjunctivitis in Tunisia, suggesting an evolutionary relationship. Epitopes recognized by neutralizing antibodies differed for the IgA1 proteases of the BPF clone and of other H. influenzae strains, including Brazilian H. influenzae biogroup aegyptius isolates from patients with noninvasive conjunctivitis. The low probability of developing cross-reacting neutralizing antibodies to the IgA1 protease of the BPF clone may contribute to the pathogenic potential of this virulent phenotype in Brazil.

Evidence of recombination and an antigenically diverse immunoglobulin A1 protease among strains of Streptococcus pneumoniae

The genetic relationships among 114 isolates of Streptococcus pneumoniae representing mainly nine serotypes that frequently cause severe childhood disease in Northern Europe were examined by use of multilocus enzyme electrophoresis. A comparison was made of the corresponding antigenic variations of excreted immunoglobulin A1 (IgA1) proteases detected by enzyme neutralization assays. Allelic variation at 13 gene loci among 70 electrophoretic types disclosed a comparatively low mean genetic diversity per locus (H = 0.319). In contrast, IgA1 proteases showed extensive antigenic diversity as 17 different inhibition types were distinguished. A lack of overall clonality was apparent from the linkage equilibrium of alleles harbored by 28 isolates chosen to represent the genetic diversity of the study population. However, certain clones, such as those marked by identical electrophoretic type, serotype, and IgA1 protease type, persisted for a sufficiently long time to enable clonal spread between distant geographic areas. Among clonally related isolates, examples illustrating a shift of capsular serotype or IgA1 protease type supported the view that recombination occurs in vivo in corresponding genes. In conclusion, over time, horizontal genetic exchange appears to be sufficiently frequent to disrupt the clonal structure otherwise generated by binary fission in natural populations of S. pneumoniae. The clonal instability combined with considerable antigenic heterogeneity renders the pneumococcal IgA1 protease less attractive as a potential component of future vaccines.

Neisseria gonorrhoeae IgA1 proteases share epitopes recognized by neutralizing antibodies

The antigenic diversity among IgA1 proteases of 61 Neisseria gonorrhoeae strains isolated during a period of 23 years and on four continents was examined in enzyme neutralization assays employing rabbit antisera raised against selected IgA1 proteases. The antigenic analyses were compared with results of iga gene-region RFLP patterns and enzyme cleavage specificity for substrate IgA1. Type 1 IgA1 proteases were antigenically uniform while six different antigenic types were detected among type 2 enzymes. Extensive cross-reactions of antibodies against the different antigenic types suggested only minor differences in relevant epitopes. Epitopes previously found to be common to all Neisseria meningitidis IgA1 proteases were also shared by all N. gonorrhoeae IgA1 proteases in the collection. Human sera from patients with gonorrhoea showed broadly cross-reactive neutralizing activity at titers comparable to those of sera from immunized rabbits. In conclusion, N. gonorrhoeae IgA1 proteases show a remarkable lack of diversity of epitopes recognized by enzyme-neutralizing antibodies. If future studies confirm that cleavage of IgA1 is an important step in gonococcal infections, Neisseria IgA1 proteases may be attractive vaccine candidates.