Genital antibody response to a parenteral gonococcal pilus vaccine

Sweet complexity: O-linked protein glycosylation in pathogenic Neisseria

The genus Neisseria, which colonizes mucosal surfaces, includes both commensal and pathogenic species that are exclusive to humans. The two pathogenic Neisseria species are closely related but cause quite different diseases, meningococcal sepsis and meningitis (Neisseria meningitidis) and sexually transmitted gonorrhea (Neisseria gonorrhoeae). Although obvious differences in bacterial niches and mechanisms for transmission exists, pathogenic Neisseria have high levels of conservation at the levels of nucleotide sequences, gene content and synteny. Species of Neisseria express broad-spectrum O-linked protein glycosylation where the glycoproteins are largely transmembrane proteins or lipoproteins localized on the cell surface or in the periplasm. There are diverse functions among the identified glycoproteins, for example type IV biogenesis proteins, proteins involved in antimicrobial resistance, as well as surface proteins that have been suggested as vaccine candidates. The most abundant glycoprotein, PilE, is the major subunit of pili which are an important colonization factor. The glycans attached can vary extensively due to phase variation of protein glycosylation (pgl) genes and polymorphic pgl gene content. The exact roles of glycosylation in Neisseria remains to be determined, but increasing evidence suggests that glycan variability can be a strategy to evade the human immune system. In addition, pathogenic and commensal Neisseria appear to have significant glycosylation differences. Here, the current knowledge and implications of protein glycosylation genes, glycan diversity, glycoproteins and immunogenicity in pathogenic Neisseria are summarized and discussed.

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.

Promising developments in gonococcal vaccines

PURPOSE OF REVIEW

While effective vaccines to prevent invasive infections by Neisseria meningitidis have been deployed around the world, development of a vaccine to prevent Neisseria gonorrhoeae has lagged. After multiple failed vaccine candidates, vaccine development for N. gonorrhoeae is showing promise for the first time in several decades. This review highlights recent progress in the field.

RECENT FINDINGS

Vaccines containing outer-membrane vesicles (OMV) have been used to manage outbreaks of the serogroup B N. meningitidis in a number of countries. Epidemiologic studies indicate these vaccination campaigns were associated with reductions in reported N. gonorrhoeae infections. Recently, a serogroup B N. meningitidis vaccine containing both recombinant antigens and OMV has been licensed through much of the world. Epidemiologic studies also demonstrate associations between 4CMenB immunization and reduced N. gonorrhoeae infections. Additionally, mathematical modeling studies have begun to identify potential strategies for vaccine deployment to maximize reduction of infections.

SUMMARY

After several decades with little progress towards an effective gonococcal vaccine, large observational studies have provided evidence that a new generation of group B N. meningitidis vaccines containing OMV have serendipitously restarted the field. Ongoing clinical trials will soon provide definitive evidence regarding the efficacy of these vaccines in preventing N. gonorrhoeae infection.

In Vitro Pre-Clinical Evaluation of a Gonococcal Trivalent Candidate Vaccine Identified by Transcriptomics

Gonorrhea, a sexually transmitted disease caused by Neisseria gonorrhoeae, poses a significant global public health threat. Infection in women can be asymptomatic and may result in severe reproductive complications. Escalating antibiotic resistance underscores the need for an effective vaccine. Approaches being explored include subunit vaccines and outer membrane vesicles (OMVs), but an ideal candidate remains elusive. Meningococcal OMV-based vaccines have been associated with reduced rates of gonorrhea in retrospective epidemiologic studies, and with accelerated gonococcal clearance in mouse vaginal colonization models. Cross-protection is attributed to shared antigens and possibly cross-reactive, bactericidal antibodies. Using a Candidate Antigen Selection Strategy (CASS) based on the gonococcal transcriptome during human mucosal infection, we identified new potential vaccine targets that, when used to immunize mice, induced the production of antibodies with bactericidal activity against N. gonorrhoeae strains. The current study determined antigen recognition by human sera from N. gonorrhoeae-infected subjects, evaluated their potential as a multi-antigen (combination) vaccine in mice and examined the impact of different adjuvants (Alum or Alum+MPLA) on functional antibody responses to N. gonorrhoeae. Our results indicated that a stronger Th1 immune response component induced by Alum+MPLA led to antibodies with improved bactericidal activity. In conclusion, a combination of CASS-derived antigens may be promising for developing effective gonococcal vaccines.

Experimental Urethral Infection with Neisseria gonorrhoeae

Gonorrhea rates and antibiotic resistance are both increasing. Neisseria gonorrhoeae (Ng) is an exclusively human pathogen and is exquisitely adapted to its natural host. Ng can subvert immune responses and undergoes frequent antigenic variation, resulting in limited immunity and protection from reinfection. Previous gonococcal vaccine efforts have been largely unsuccessful, and the last vaccine to be tested in humans was more than 35 years ago. Advancing technologies and the threat of untreatable gonorrhea have fueled renewed pursuit of a vaccine as a long-term sustainable solution for gonorrhea control. Despite the development of a female mouse model of genital gonococcal infection two decades ago, correlates of immunity or protection remain largely unknown, making the gonococcus a challenging vaccine target. The controlled human urethral infection model of gonorrhea (Ng CHIM) has been used to study gonococcal pathogenesis and the basis of anti-gonococcal immunity. Over 200 participants have been inoculated without serious adverse events. The Ng CHIM replicates the early natural course of urethral infection. We are now at an inflexion point to pivot the use of the model for vaccine testing to address the urgency of improved gonorrhea control. Herein we discuss the need for gonorrhea vaccines, and the advantages and limitations of the Ng CHIM in accelerating the development of gonorrhea vaccines.

Progress Toward a Gonococcal Vaccine: The Way Forward

The concept of immunizing against gonorrhea has received renewed interest because of the recent emergence of strains of Neisseria gonorrhoeae that are resistant to most currently available antibiotics, an occurrence that threatens to render gonorrhea untreatable. However, despite efforts over many decades, no vaccine has yet been successfully developed for human use, leading to pessimism over whether this goal was actually attainable. Several factors have contributed to this situation, including extensive variation of the expression and specificity of many of the gonococcal surface antigens, and the ability of N. gonorrhoeae to resist destruction by complement and other innate immune defense mechanisms. The natural host restriction of N. gonorrhoeae for humans, coupled with the absence of any definable state of immunity arising from an episode of gonorrhea, have also complicated efforts to study gonococcal pathogenesis and the host's immune responses. However, recent findings have elucidated how the gonococcus exploits and manipulates the host's immune system for its own benefit, utilizing human-specific receptors for attachment to and invasion of tissues, and subverting adaptive immune responses that might otherwise be capable of eliminating it. While no single experimental model is capable of providing all the answers, experiments utilizing human cells and tissues in vitro, various in vivo animal models, including genetically modified strains of mice, and both experimental and observational human clinical studies, have combined to yield important new insight into the immuno-pathogenesis of gonococcal infection. In turn, these have now led to novel approaches for the development of a gonococcal vaccine. Ongoing investigations utilizing all available tools are now poised to make the development of an effective human vaccine against gonorrhea an achievable goal within a foreseeable time-frame.

Gonorrhea - an evolving disease of the new millennium

Etiology, transmission and protection: Neisseria gonorrhoeae (the gonococcus) is the etiological agent for the strictly human sexually transmitted disease gonorrhea. Infections lead to limited immunity, therefore individuals can become repeatedly infected. Pathology/symptomatology: Gonorrhea is generally a non-complicated mucosal infection with a pustular discharge. More severe sequellae include salpingitis and pelvic inflammatory disease which may lead to sterility and/or ectopic pregnancy. Occasionally, the organism can disseminate as a bloodstream infection. Epidemiology, incidence and prevalence: Gonorrhea is a global disease infecting approximately 60 million people annually. In the United States there are approximately 300, 000 cases each year, with an incidence of approximately 100 cases per 100,000 population. Treatment and curability: Gonorrhea is susceptible to an array of antibiotics. Antibiotic resistance is becoming a major problem and there are fears that the gonococcus will become the next "superbug" as the antibiotic arsenal diminishes. Currently, third generation extended-spectrum cephalosporins are being prescribed. Molecular mechanisms of infection: Gonococci elaborate numerous strategies to thwart the immune system. The organism engages in extensive phase (on/off switching) and antigenic variation of several surface antigens. The organism expresses IgA protease which cleaves mucosal antibody. The organism can become serum resistant due to its ability to sialylate lipooligosaccharide in conjunction with its ability to subvert complement activation. The gonococcus can survive within neutrophils as well as in several other lymphocytic cells. The organism manipulates the immune response such that no immune memory is generated which leads to a lack of protective immunity.

Antibodies with higher bactericidal activity induced by a Neisseria gonorrhoeae Rmp deletion mutant strain

Neisseria gonorrhoeae (N. gonorrhoeae) outer membrane protein reduction modifiable protein (Rmp) has strong immunogenicity. However, anti-Rmp antibodies block rather than preserve the antibacterial effects of protective antibodies, which hampers the development of vaccines for gonococcal infections. We herein constructed an Rmp deletion mutant strain of N. gonorrhoeae by gene homologous recombination. The 261–460 nucleotide residues of Rmp gene amplified from N. gonorrhoeae WHO-A strain were replaced with a kanamycin-resistant Kan gene amplified from pET-28a. The resultant hybridized DNA was transformed into N. gonorrhoeae WHO-A strain. PCR was used to screen the colonies in which wild-type Rmp gene was replaced with a mutant gene fragment. Western blotting revealed that the Rmp deletion mutant strain did not express Rmp protein. Rmp deletion did not alter the morphological and Gram staining properties of the mutant strain that grew slightly more slowly than the wild-type one. Rmp gene mutated stably throughout 25 generations of passage. Antibody-mediated complement-dependent cytotoxicity assay indicated that the antibodies induced by the mutant strain had evidently higher bactericidal activities than those induced by the wild-type strain. Further modification of the Rmp deletion mutant strain is still required in the development of novel live attenuated vaccines for gonorrhea by Opa genes deletion or screening of phenotypic variant strains that do not express Opa proteins.

Vaccines for gonorrhea: can we rise to the challenge?

Immune responses to the gonococcus after natural infection ordinarily result in little immunity to reinfection, due to antigenic variation of the gonococcus, and redirection or suppression of immune responses. Brinton and colleagues demonstrated that parenteral immunization of male human volunteers with a purified pilus vaccine gave partial protection against infection by the homologous strain. However, the vaccine failed in a clinical trial. Recent vaccine development efforts have focused on the female mouse model of genital gonococcal infection. Here we discuss the state of the field, including our unpublished data regarding efficacy in the mouse model of either viral replicon particle (VRP) vaccines, or outer membrane vesicle (OMV) vaccines. The OMV vaccines failed, despite excellent serum and mucosal antibody responses. Protection after a regimen consisting of a PorB-VRP prime plus recombinant PorB boost was correlated with apparent Th1, but not with antibody, responses. Protection probably was due to powerful adjuvant effects of the VRP vector. New tools including novel transgenic mice expressing human genes required for gonococcal infection should enable future research. Surrogates for immunity are needed. Increasing antimicrobial resistance trends among gonococci makes development of a vaccine more urgent.

Tolerance and protection against infection in the genital tract

The genital tract is a unique immunological environment that must support the reproductive function and resist infection. Particularly in the female tract, immunoregulatory and immunosuppressive activities that permit the growth of the fetus create an environment that can readily be exploited by microbes that have become well-adapted to this location. Cellular and molecular mediators of immune responses differ from those found at other mucosal surfaces. Mechanisms of immune response induction and delivery, as well as immune effector functions at the genital mucosae need to be considered in the development of vaccines against infections of the genital tract.

Genetic, structural, and antigenic analyses of glycan diversity in the O-linked protein glycosylation systems of human Neisseria species

Bacterial capsular polysaccharides and lipopolysaccharides are well-established ligands of innate and adaptive immune effectors and often exhibit structural and antigenic variability. Although many surface-localized glycoproteins have been identified in bacterial pathogens and symbionts, it not clear if and how selection impacts associated glycoform structure. Here, a systematic approach was devised to correlate gene repertoire with protein-associated glycoform structure in Neisseria species important to human health and disease. By manipulating the protein glycosylation (pgl) gene content and assessing the glycan structure by mass spectrometry and reactivity with monoclonal antibodies, it was established that protein-associated glycans are antigenically variable and that at least nine distinct glycoforms can be expressed in vitro. These studies also revealed that in addition to Neisseria gonorrhoeae strain N400, one other gonococcal strain and isolates of Neisseria meningitidis and Neisseria lactamica exhibit broad-spectrum O-linked protein glycosylation. Although a strong correlation between pgl gene content, glycoform expression, and serological profile was observed, there were significant exceptions, particularly with regard to levels of microheterogeneity. This work provides a technological platform for molecular serotyping of neisserial protein glycans and for elucidating pgl gene evolution.

Limited local and systemic antibody responses to Neisseria gonorrhoeae during uncomplicated genital infections

Repeated infections with Neisseria gonorrhoeae are common among patients attending sexually transmitted disease clinics. We examined whether previous infections or site of infection altered the local and systemic antigonococcal antibody levels in males and females. Antibodies against N. gonorrhoeae MS11 and the patients' homologous infecting isolates were measured by enzyme-linked immunosorbent assay. In general, the local and systemic immune responses to gonococci were extremely modest. There was a slight increase in serum immunoglobulin G (IgG) against the MS11 strain and the homologous isolates in infected males. Levels of serum IgA1 antibodies against MS11 were slightly higher in infected than in uninfected females. A history of previous infections with N. gonorrhoeae did not alter the antibody levels in patients with a current infection, suggesting that immunological memory is not induced by uncomplicated gonococcal infections. Antibody responses to infected subjects' homologous isolates were observed in cervical mucus; IgA1 levels increased while IgG levels decreased. The decline in mucosal IgG against the homologous isolates was less common in subjects having both rectal and cervical infections; otherwise, no effect of rectal involvement was observed. The absence of substantially higher antibody levels to gonococci where there is infection at a site known to contain organized lymphoid tissue suggests that the low levels of responses to uncomplicated infections may not be due simply to an absence of inductive sites in the genital tract. We propose that in addition to its potential ability to avoid the effects of an immune response, N. gonorrhoeae does not elicit strong humoral immune responses during uncomplicated genital infections.

The importance of mucosal immunology to problems in human reproduction

The field of mucosal immunology is making rapid advances towards establishing the molecular basis of mucosal defense mechanisms and the development of mucosal vaccines. Research on the mucosal immunology of male and female reproductive tract tissues is benefiting from these advances, as well as from current investigations on specialized immunologic features of the reproductive tract. This knowledge may soon be applicable to solutions for many important problems concerning human reproduction, such as fertility regulation and the current epidemic of sexually transmitted diseases, including AIDS.

Questions about gonococcal pilus phase- and antigenic variation

Pathogenic organisms inhabit one of several defined locations within a host where temperature, pH, and nutrients are relatively constant. While the microorganism must adapt to different environments within the host, the host immune system is the most formidable predator that can limit the growth of a pathogen. Neisseria gonorrhoeae (the gonococcus, Gc) is the causative agent of gonorrhoea, and has evolved several systems for varying the antigenicity of different surface antigens, presumably to help evade the effects of the human immune system. The On/Off/On phase variation of surface structure expression also alters the antigenic characteristics of the bacterial cell surface. Antigenic variation of the major subunit of the pilus, pilin, occurs by unidirectional, homologous recombination between a silent locus and the expression locus. The silent loci lie from 1 to 900 kb from the expression locus in the chromosome yet all can donate their sequences to the expression locus. The genetic composition of the pilin loci of two Gc strains has been elucidated, and the types of changes that lead to altered forms of the pilus have been extensively characterized. However, little is known about the precise molecular mechanisms used to allow high-frequency, non-reciprocal, chromosomal recombination between pilin loci or about what regulates the process of maintaining chromosome fidelity.

Detection of antibodies to Shigella lipopolysaccharide in urine after natural Shigella infection or vaccination

The purpose of the present study was to explore the possibility of detecting antibodies to Shigella sonnei lipopolysaccharide (LPS) in urine after infection or vaccination. Urinary immunoglobulin A (IgA) and IgG antibodies and specific IgA secretory protein against S. sonnei LPS were measured by enzyme-linked immunosorbent assay (ELISA), after adjustment for urine concentration. A significant antibody level was defined as one above a cutoff value calculated from the geometric mean + 2 standard deviations of urinary anti-S. sonnei LPS levels in 43 healthy hepatitis B vaccinees (controls). Of 11 culture-proven cases of S. sonnei shigellosis, at convalescence 9 (82%) had significantly elevated levels of urinary antibodies to the homologous LPS. The S. sonnei conjugate vaccine, composed of S. sonnei O-specific polysaccharide covalently bound to recombinant exoprotein A of Pseudomonas aeruginosa, elicited a significant urine IgA or IgG anti-LPS response in 60% (6 of 10), 56% (9 of 16) 43% (16 of 37), and 14% (3 of 21) of the volunteers at 2 weeks, 6 weeks, 6 months, and 12 months after vaccination, respectively. The specificity of the urine antibody response to S. sonnei LPS was documented by the total lack of response in subjects who received parenteral Shigella flexneri 2a-recombinant exoprotein A conjugate (69 urine samples) or meningoccal tetravalent control vaccines (4 urine samples). All the volunteers who lacked a significant response to S. sonnei LPS in serum also lacked such response in urine samples. Seventy-four percent of the volunteers with a significant IgA or IgG anti-LPS response in serum at convalescence or 14 days after vaccination showed a similar response in urine. The ratio of the titer of secretory protein bound to IgA anti-S. sonnei LPS in urine to that in serum was 303 times higher than the ratio of anti-S. sonnei LPS total IgA titer in urine to that in serum, indicating that the urine IgA is of secretory origin. These findings suggest the possible use of urinary Shigella LPS antibodies as markers of systemic and secretory immune responses after natural infection or vaccination. At this stage, because of its limited sensitivity, the detection by ELISA of Shigella LPS antibodies in urine cannot replace the same assay in serum as a definitive test in an individual with a negative result.

Serovar specific immunity to Neisseria gonorrhoeae: does it exist?

OBJECTIVE

To determine whether the host immune response to gonorrhoea provides limited serovar specific protection from reinfection.

SUBJECTS

508 episodes of gonorrhoea diagnosed at a city centre genitourinary medicine clinic including 22 patients with multiple infections over a 4 year period.

METHODS

Patients with recurrent gonococcal infection were analysed with respect to the initial and subsequent serovars isolated.

RESULTS

No significant difference was seen in the prevalence of serovars isolated following a repeat infection compared with those without repeat infections. The site of the initial infection did not appear to influence the subsequent serovar isolated.

CONCLUSION

We found no evidence of serovar specific immunity in our population. It remains possible that populations with a higher prevalence of gonorrhoea and more frequent infections may have a quantitatively greater immune response.

Inhibitory effect of saliva from secretors and non-secretors on binding of meningococci to epithelial cells

Carriage of Neisseria meningitidis B:4:P1.15 was higher among non-secretors during a school outbreak of meningitis; non-secretors had lower levels of anti-meningococcal salivary IgM. Flow cytometry was used to assess effects of secretor and non-secretor saliva on binding of B:4:P1.15 to buccal epithelial cells: (1) to assess inhibition by IgA and IgM; and (2) to assess contributions of salivary antibodies to inhibitory activities. Greater inhibition was obtained with secretor saliva: pooled (P = 0.049); fresh (P = 0.0001). Purified IgA (P = 0.02) and IgM (P = 0.03) were equally inhibitory. After absorption of anti-meningococcal antibodies, there was still significant inhibitory activity in the pools: secretors (P = 0.018); non-secretors (P = 0.005). These results indicate that both secretory immunoglobulins and other factors contribute to protection against colonisation by meningococci and might explain the increased carriage of B:4:1.15 in this population.

Vaccines for bacterial sexually transmitted infections: a realistic goal?

Bacterial infections of the genital tract (gonorrhea, chlamydia, chancroid, syphilis) are common and cause significant morbidity. Their importance is heightened by recent appreciation of their roles in facilitation of transmission of the human immunodeficiency virus (HIV). Each is capable of causing repeated infections, suggesting lack of permanent broadly effective immunity. An effective vaccine has yet to be developed for any of these diseases. Rapid progress in understanding the molecular basis for pathogenesis of infection, including mechanisms for escape from otherwise effective immune surveillance and mechanisms for causing injury to host cells, has stimulated renewed efforts to make vaccines for some of these infections. Progress has been greatest for Neisseria gonorrhoeae and Chlamydia trachomatis. Present emphasis is on the major or principal outer membrane proteins of N. gonorrhoeae and C. trachomatis, based on evidence for neutralizing antibodies directed against surface-exposed variable domains of each of these proteins. Other surface-exposed proteins, including the iron-repressible transferrin receptor in gonococci and certain heat-shock proteins in chlamydia, also may be targets for vaccines. Although much remains to be learned, cautious optimism is warranted.

Fimbriae of Branhamella catarrhalis as possible mediators of adherence to pharyngeal epithelial cells

This study attempted to elucidate the role of fimbriae in the adherence of B. catarrhalis to human oropharyngeal epithelial cells. Antifimbrial immune serum was prepared by immunization of rabbit with whole fimbriated bacteria, and adsorption of the serum with a nonfimbriated B. catarrhalis strain. After pretreatment with the antifimbrial antiserum, the adherence of fimbriated B. catarrhalis to human epithelial cells was significantly decreased (p < 0.05). The adherence was also significantly (p < 0.001) decreased by trypsin treatment. Electron microscopy revealed destruction of fimbriae after trypsin treatment. These observations suggest that fimbriae are involved in the adherence of B. catarrhalis to epithelial cells.

Humoral immune response to Bacteroides gingivalis fimbrial antigen in mice

Bacteroides gingivalis fimbrial antigen incorporated into liposomes, but not in Tris-HCl buffer, significantly raised the levels of anti-fimbriae antibodies in serum, particularly of the IgG class, after oral primary and booster immunizations in BALB/c mice. An approximately linear relationship was observed between the dose of fimbrial antigen and the level of fimbriae-specific antibodies produced; antibody production reached its maximum at an immunization dosage of 500 micrograms of fimbriae per mouse. Fimbriae-specific antibody production was enhanced by use of a semi-synthetic adjuvant, a stearoyl derivative of sodium beta-N-acetylglucosaminyl-(1----4)-N-acetylmuramyl-L-alanyl-D-isoglutaminyl-(L) - stearoyl-(D)-meso-diamino-pimelic acid-(D)-amide-D-alanine (GM)-53) in liposomes. High anti-fimbriae antibody levels in serum and saliva were maintained for several months in the mice that had received two orally administered boosters of fimbrial antigen with GM-53 in liposomes. Salivary anti-fimbriae antibody levels, particularly of the IgA class, were markedly raised.

Lung humoral response to Pseudomonas species

Immunoglobulin G (IgG) is quantitatively the predominent immunoglobulin protein in the distal airway of the human host. IgG enters the distal lung from circulating pools and plasma cells located largely in the interstitium. Although all four IgG subclasses are present in human lung secretions, only subclasses G3 and, to a lesser degree, G1 attach to pulmonary macrophage membrane receptors. IgG opsonic antibodies are essential for the optimal clearance of a very troubling pathogen. Pseudomonas aeruginosa. Nosocomial pneumonia caused by this gram-negative bacillus responds poorly to potent antimicrobial agents and is associated with a 70% mortality. To a great extent the morbidity and mortality resulting from nosocomial pneumonia caused by Pseudomonas spp. are attributable to ineffective humoral immune response to this bacterium. IgG2 antibodies in response to pseudomonal lipopolysaccharide are poorly opsonic in the macrophage system, and derepression of the potent pseudomonal elastase, an enzyme with broad substrate specificity, contributes to the disruption of other IgG antibodies.

Probing the surface of Neisseria gonorrhoeae: immunoelectron microscopic studies to localize cyanogen bromide fragment 2 in gonococcal pili

Common epitopes accessible to antibody on purified macromolecules or structurally altered gonococci may not be accessible to antibody when those macromolecules are in their native state on the surface of intact organisms. To determine the immunologic accessibility of cyanogen bromide fragment 2 (CNBr2), a portion of the gonococcal pilin molecule that is common to all gonococcal strains on the surface of viable gonococci, probes composed of specific CNBr2 antibodies linked to gold spheres were manufactured. When whole piliated gonococci were exposed to these anti-CNBr2 immunological probes and examined using transmission electron microscopy, no significant marketing of native pili was evident. These probes, however, detected CNBr2 in purified form. The epitopes encompassed within the CNBr2 portion of pili appear to be inaccessible to anti-CNBr2 probes within native gonococcal pili.

Pilins of Bacteroides nodosus: molecular basis of serotypic variation and relationships to other bacterial pilins

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Structural and serological relatedness of Haemophilus influenzae type b pili

The structural and serological relatedness of the pilus proteins of several isolates of Haemophilus influenzae type b cultured from patients with invasive disease and from different anatomic sites within the same patient was examined. Epithelial cell-adherent variants of 25 nonadherent parent isolates were obtained by selection for organisms that adhered to human erythrocytes. Outer membrane protein analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed the presence of an additional 24- to 24.5-kilodalton protein among all adherent variants but absent from all nonadherent parent isolates. Polyclonal rabbit antiserum against the intact native pilus protein of H. influenzae M43 cross-reacted with 20 of 25 adherent H. influenzae in both immunodot and slide-agglutination assays. No differences in reactivity among isolates cultured from more than one anatomic site in the same patient were noted. Anti-M43 pilus antiserum had bactericidal activity against both the homologous strain and a heterologous strain that demonstrated serologic identity in the immunodot and slide agglutination assays. The adherence of these strains to human epithelial cells in vitro was inhibited by Fab fragments purified from the antipilus antiserum. These data indicate that a remarkable degree of homogeneity in pilin subunit size exists among the pili of H. influenzae type b and that major antigenic determinants are shared among most of these pili. Also, antibodies directed against H. influenzae pilus proteins may be able to contribute to host defenses through serum bactericidal activity and by blocking the adherence of this bacterium to host epithelial cells.

Fimbria-specific antibodies in serum and saliva of mice immunized with Actinomyces viscosus T14V fimbriae

Fimbria-specific antibody responses were compared in mice immunized with purified fimbrial adhesins in the region of the submandibular gland (i.e., local site) or at a remote site in the back. One hundred micrograms of fimbriae isolated from Actinomyces viscosus T14V was used as the vaccine. Four subcutaneous injections of the vaccine in the local site induced greater amounts of fimbria-specific immunoglobulin G (IgG) in serum and saliva than three injections. However, there was no difference in the response of fimbria-specific IgA in serum and saliva. Fimbria-specific IgG in serum and saliva were first detected 21 days after the primary immunization at both the local or remote sites. Fimbria-specific IgA in serum was first detected 28 days after the primary immunization at both the local or remote sites. However, fimbria-specific IgA in saliva occurred only in mice immunized with the fimbrial vaccine at the local site and was first detected 14 days after the primary immunization. Both serum and saliva from mice immunized 4 times with the fimbrial vaccine in the local site inhibited in vitro adsorption of strain T14V cells to hydroxyapatite beads pretreated with normal mouse saliva, whereas adsorption of strain T14V cells suspended in serum and saliva from sham-immunized animals was not inhibited. Collectively, these data suggest that mice immunized locally in the submandibular gland region with a vaccine composed of purified fimbrial adhesins provide a potential model for evaluating the efficacy of fimbria-specific antibodies in saliva to inhibit strain T14V colonization of tooth surfaces.

Modulation of Actinomyces viscosus colonization of mouse teeth in vivo by immunization with fimbrial adhesins

Experiments were performed to determine whether immunization of mice with fimbrial adhesins isolated from Actinomyces viscosus T14V could modulate infection of tooth surfaces in animals challenged with the homologous strain. Saliva and sera from animals immunized in the submandibular gland region contained elevated levels of fimbria-specific immunoglobulin A (IgA) and IgG, whereas saliva and sera from sham-immunized animals did not. There was a statistically significant inverse correlation between the presence of fimbria-specific antibodies in saliva and serum and the levels of bacterial colonization on molar tooth surfaces. These results suggest that fimbrial adhesins may effectively modulate infection of tooth surfaces by periodontopathic bacteria.

Pili of Neisseria meningitidis. Analysis of structure and investigation of structural and antigenic relationships to gonococcal pili

To provide information useful for the design of a pilus vaccine effective for the prevention of both meningococcal and gonococcal disease, the electron microscopic morphology of meningococcal pili and the structural and antigenic relationships of meningococcal pili to gonococcal pili were investigated. Meningococcal pili were 4-6 nm in width, extended 500-6,000 nm from the organism surface, and occurred singly or in bundles composed of 8-10 pili per bundle. Meningococcal pilin varied between 17,250 and 20,600 daltons. Pilin was present in outer membrane preparations of some meningococcal isolates that were nonpiliated by electron microscopic examination. Antibodies to gonococcal pili, cyanogen bromide cleavage fragments of gonococcal pilin, or synthetic peptide analogues corresponding to regions of the gonococcal pilin sequence, were used to detect common meningococcal and gonococcal antigenic determinants that might indicate the existence of a conserved sequence beyond residue 29. Antibody to intact gonococcal pili or to the variable CNBR-3 region of gonococcal pilin detected little shared antigenicity with meningococcal pilin. However, pilin from all tested meningococcal isolates reacted with antibody to the CNBR-2 fragment of gonococcal pilin, a region highly conserved among gonococcal strains. Meningococcal pilins were also broadly crossreactive with antibody to a synthetic peptide corresponding to residues 69-84 of the gonococcal sequence, a part of the CNBR-2 region that appears to be critical for gonococcal receptor-binding function. If a sequence similar to 69-84 is also important for receptor-binding function in meningococcal pili, a peptide corresponding to this region may elicit antibodies that block the adherence function of pili elaborated by both Neisseria gonorrhoeae and N. meningitidis.

Mechanisms of antibacterial immunity of mucous membranes

A survey based on both literary data and the authors own results, concerning the mechanisms of sIgA-mediated antibacterial immunity, is presented. Secretory IgA is characterized as a specific component of the immune system of mucous membranes, which can recognize harmful bacterial and distinguish them from indigenous microflora physiologically colonizing the mucous membranes, to fix them to the mucous membrane surface and to direct further factors, such as mucin, lysozyme, etc. (which form the effector component of the mucous membrane immunity system) for their final inactivation and neutralization.

Induction of optimal mucosal antibody responses: effects of age, immunization route(s), and dosing schedule in rats

The antitoxin response in intestinal mucosa was studied in rats immunized either intestinally or by combined parenteral and intestinal dosing with cholera toxin or cholera toxoid. Attention was given to the duration of enteric priming and the magnitude and time course of mucosal anti-cholera toxin responses in rats of defined age. Cholera toxin given only intraduodenally was a more efficient priming immunogen in young rats than in older rats and caused priming that lasted at least 32 weeks; repeated enteric doses increased local priming and repeatedly evoked vigorous mucosal anti-cholera toxin responses which occurred rapidly and declined slowly. Results differed when a portion of the immunizing regimen was parenteral. Cholera toxoid given intraperitoneally (i.p.) caused mucosal priming that peaked promptly and then rapidly declined; parenteral boosting after enteric priming was much more effective given i.p. than subcutaneously; moreover, the booster response was brief, virtually disappearing within 11 days, and could not be reproduced by a second i.p. immunization. These results accord with evidence that parenteral immunization both stimulates and suppresses mucosal secretory immunoglobulin A responses, whereas local immunization is not known to be suppressive. Evidence for parenterally induced suppression was the rapid decline in mucosal priming after i.p. immunization, the shortened mucosal antibody response after i.p. immunization, and possibly the inability to parenterally evoke a booster response twice. In these studies, the level of priming observed at different intervals after parenteral, enteric, or combined immunization appeared to reflect the sum of priming and suppressive effects evoked by the preceding immunization(s).