The presence of complement in human cervical mucus and its possible relevance to infertility in women with complement-dependent sperm-immobilizing antibodies

Preclinical efficacy of a cell division protein candidate gonococcal vaccine identified by artificial intelligence

IMPORTANCE

Vaccines to curb the global spread of multidrug-resistant gonorrhea are urgently needed. Here, 26 vaccine candidates identified by an artificial intelligence-driven platform (Efficacy Discriminative Educated Network[EDEN]) were screened for efficacy in the mouse vaginal colonization model. Complement-dependent bactericidal activity of antisera and the EDEN protective scores both correlated positively with the reduction in overall bacterial colonization burden. NGO1549 (FtsN) and NGO0265, both involved in cell division, displayed the best activity and were selected for further development. Both antigens, when fused to create a chimeric protein, elicited bactericidal antibodies against a wide array of gonococcal isolates and significantly attenuated the duration and burden of gonococcal colonization of mouse vaginas. Protection was abrogated in mice that lacked complement C9, the last step in the formation of the membrane attack complex pore, suggesting complement-dependent bactericidal activity as a mechanistic correlate of protection of the vaccine. FtsN and NGO0265 represent promising vaccine candidates against gonorrhea.

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.

Functional characterization of the gonococcal polyphosphate pseudo-capsule

Neisseria gonorrhoeae is an exclusively human pathogen able to evade the host immune system through multiple mechanisms. Gonococci accumulate a large portion of phosphate moieties as polyphosphate (polyP) on the exterior of the cell. Although its polyanionic nature has suggested that it may form a protective shield on the cell surface, its role remains controversial. Taking advantage of a recombinant His-tagged polyP-binding protein, the presence of a polyP pseudo-capsule in gonococcus was demonstrated. Interestingly, the polyP pseudo-capsule was found to be present in specific strains only. To investigate its putative role in host immune evasion mechanisms, such as resistance to serum bactericidal activity, antimicrobial peptides and phagocytosis, the enzymes involved in polyP metabolism were genetically deleted, generating mutants with altered polyP external content. The mutants with lower polyP content on their surface compared to the wild-type strains, became sensitive to complement-mediated killing in presence of normal human serum. Conversely, naturally serum sensitive strains that did not display a significant polyP pseudo-capsule became resistant to complement in the presence of exogenous polyP. The presence of polyP pseudo-capsule was also critical in the protection from antibacterial activity of cationic antimicrobial peptide, such as cathelicidin LL-37. Results showed that the minimum bactericidal concentration was lower in strains lacking polyP than in those harboring the pseudo-capsule. Data referring to phagocytic killing resistance, assessed by using neutrophil-like cells, showed a significant decrease in viability of mutants lacking polyP on their cell surface in comparison to the wild-type strain. The addition of exogenous polyP overturned the killing phenotype of sensitive strains suggesting that gonococcus could exploit environmental polyP to survive to complement-mediated, cathelicidin and intracellular killing. Taken together, data presented here indicate an essential role of the polyP pseudo-capsule in the gonococcal pathogenesis, opening new perspective on gonococcal biology and more effective treatments.

Neisseria gonorrhoeae co-opts C4b-binding protein to enhance complement-independent survival from neutrophils

Neisseria gonorrhoeae (Gc) is a human-specific pathogen that causes the sexually transmitted infection gonorrhea. Gc survives in neutrophil-rich gonorrheal secretions, and recovered bacteria predominantly express phase-variable, surface-expressed opacity-associated (Opa) proteins (Opa+). However, expression of Opa proteins like OpaD decreases Gc survival when exposed to human neutrophils ex vivo. Here, we made the unexpected observation that incubation with normal human serum, which is found in inflamed mucosal secretions, enhances survival of Opa+ Gc from primary human neutrophils. We directly linked this phenomenon to a novel complement-independent function for C4b-binding protein (C4BP). When bound to the bacteria, C4BP was necessary and sufficient to suppress Gc-induced neutrophil reactive oxygen species production and prevent neutrophil phagocytosis of Opa+ Gc. This research identifies for the first time a complement-independent role for C4BP in enhancing the survival of a pathogenic bacterium from phagocytes, thereby revealing how Gc exploits inflammatory conditions to persist at human mucosal surfaces.

Efficacy of an Experimental Gonococcal Lipooligosaccharide Mimitope Vaccine Requires Terminal Complement

A safe and effective vaccine against multidrug-resistant gonorrhea is urgently needed. An experimental peptide vaccine called TMCP2 that mimics an oligosaccharide epitope in gonococcal lipooligosaccharide, when adjuvanted with glucopyranosyl lipid adjuvant-stable emulsion, elicits bactericidal immunoglobulin G and hastens clearance of gonococci in the mouse vaginal colonization model. In this study, we show that efficacy of TMCP2 requires an intact terminal complement pathway, evidenced by loss of activity in C9-/- mice or when C7 function was blocked. In conclusion, TMCP2 vaccine efficacy in the mouse vagina requires membrane attack complex. Serum bactericidal activity may serve as a correlate of protection for TMCP2.

Production and characterization of a human antisperm monoclonal antibody against CD52g for topical contraception in women

BACKGROUND

Approximately 40% of human pregnancies are unintended, indicating a need for more acceptable effective contraception methods. New antibody production systems make it possible to manufacture reagent-grade human monoclonal antibodies (mAbs) for clinical use. We used the Nicotiana platform to produce a human antisperm mAb and tested its efficacy for on-demand topical contraception.

METHODS

Heavy and light chain variable region DNA sequences of a human IgM antisperm antibody derived from an infertile woman were inserted with human IgG₁ constant region sequences into an agrobacterium and transfected into Nicotiana benthamiana. The product, an IgG₁ mAb ["Human Contraception Antibody" (HCA)], was purified on Protein A columns, and QC was performed using the LabChip GXII Touch protein characterization system and SEC-HPLC. HCA was tested for antigen specificity by immunofluorescence and western blot assays, antisperm activity by sperm agglutination and complement dependent sperm immobilization assays, and safety in a human vaginal tissue (EpiVaginal™) model.

FINDINGS

HCA was obtained at concentrations ranging from 0.4 to 4 mg/ml and consisted of > 90% IgG monomers. The mAb specifically reacted with a glycan epitope on CD52g, a glycoprotein produced in the male reproductive tract and found in abundance on sperm. HCA potently agglutinated sperm under a variety of relevant physiological conditions at concentrations ≥ 6.25 µg/ml, and mediated complement-dependent sperm immobilization at concentrations ≥ 1 µg/ml. HCA and its immune complexes did not induce inflammation in EpiVaginal™ tissue.

INTERPRETATION

HCA, an IgG1 mAb with potent sperm agglutination and immobilization activity and a good safety profile, is a promising candidate for female contraception.

FUNDING

This research was supported by grants R01 HD095630 and P50HD096957 from the National Institutes of Health.

Role of the Gonococcal Neisserial Heparin Binding Antigen in Microcolony Formation, and Serum Resistance and Adherence to Epithelial Cells

The sexually transmitted infection gonorrhoea is on the rise worldwide and an increased understanding of the mechanisms of colonization and pathogenesis of Neisseria gonorrhoeae is required to aid development of new treatment and prevention strategies. In the current study, we investigate the neisserial heparin-binding antigen (NHBA) of N. gonorrhoeae and confirm its role in binding to several glycans, including heparin, and identify interactions of NHBA with both gonococcal and host cells. Furthermore, we report that a gonococcal nhba mutant displays decreased cell aggregation and microcolony formation, as well as reduced survival in human serum and reduced adherence to human cervical and urethral epithelial cells, relative to the wild-type strain. These data indicate that the gonococcal NHBA contributes to several aspects of the colonization and survival of N. gonorrhoeae and may be a target for new antimicrobial or vaccines.

Reproductive immunology in viviparous mammals: evolutionary paradox of interactions among immune mechanisms and autologous or allogeneic gametes and semiallogeneic foetuses

Literally, reproductive immunology was born in bovine on-farm reproduction where seminal experiments intended for developing methods for embryo transfer in cattle were performed. Actually, these experiments led to two of major concepts and fundamental principles of reproductive immunology using the bovine species as a model for biomedical research, namely the concept of acquired immunological tolerance and the paradox of the semiallogeneic bovine foetus whereby such organism can develop within an immunologically competent host. Peter Medawar, a scientist who together with Frank Macfarlande Burnet shared the 1960 Nobel Prize in physiology or medicine for discovery of acquired immunological tolerance, while studying dizygotic cattle twins, thereby giving birth to reproductive immunology. Also, these findings significantly influenced development of organ transplants and showed that using farm animals as models for studying transplantation immunology had general relevance for mammalian biology and health including those of humans. However, the interest for further research of the fascinating maternal immune influences on pregnancy and perinatal outcomes and of the prevention and treatment of immunologically mediated reproductive disorders in viviparous mammals of veterinary relevance by veterinary immunologists and reproductive clinicians have been very scarce regarding the application of nonspecific immunomodulatory agents for prevention and treatment of subfertility and infertility in pigs and cattle, but still broadening knowledge in this area and hold great potential for improving such therapy in the future. The aim of the current overview is to provide up-to-date information and explaining/translating relevant immunology phenomena into veterinary practice for specialists and scientists/clinicians in reproduction of animals.

Complement interactions with the pathogenic Neisseriae: clinical features, deficiency states, and evasion mechanisms

Neisseria gonorrhoeae causes the sexually transmitted infection gonorrhea, while Neisseria meningitidis is an important cause of bacterial meningitis and sepsis. Complement is a central arm of innate immune defenses and plays an important role in combating Neisserial infections. Persons with congenital and acquired defects in complement are at a significantly higher risk for invasive Neisserial infections such as invasive meningococcal disease and disseminated gonococcal infection compared to the general population. Of note, Neisseria gonorrhoeae and Neisseria meningitidis can only infect humans, which in part may be related to their ability to evade only human complement. This review summarizes the epidemiologic and clinical aspects of Neisserial infections in persons with defects in the complement system. Mechanisms used by these pathogens to subvert killing by complement and preclinical studies showing how these complement evasion strategies may be used to counteract the global threat of meningococcal and gonococcal infections are discussed.

C4BP-IgM protein as a therapeutic approach to treat Neisseria gonorrhoeae infections

Gonorrhea is a sexually transmitted infection with 87 million new cases per year globally. Increasing antibiotic resistance has severely limited treatment options. A mechanism that Neisseria gonorrhoeae uses to evade complement attack is binding of the complement inhibitor C4b-binding protein (C4BP). We screened 107 porin B1a (PorB1a) and 83 PorB1b clinical isolates randomly selected from a Swedish strain collection over the last 10 years and noted that 96/107 (89.7%) PorB1a and 16/83 (19.3%) PorB1b bound C4BP; C4BP binding substantially correlated with the ability to evade complement-dependent killing (r = 0.78). We designed 2 chimeric proteins that fused C4BP domains to the backbone of IgG or IgM (C4BP-IgG; C4BP-IgM) with the aim of enhancing complement activation and killing of gonococci. Both proteins bound gonococci (KD C4BP-IgM = 2.4 nM; KD C4BP-IgG 980.7 nM), but only hexameric C4BP-IgM efficiently outcompeted heptameric C4BP from the bacterial surface, resulting in enhanced complement deposition and bacterial killing. Furthermore, C4BP-IgM substantially attenuated the duration and burden of colonization of 2 C4BP-binding gonococcal isolates but not a non-C4BP-binding strain in a mouse vaginal colonization model using human factor H/C4BP-transgenic mice. Our preclinical data present C4BP-IgM as an adjunct to conventional antimicrobials for the treatment of gonorrhea.

Latheef S, Sharun K, Khurana SK, K. A, Tiwari R, Bhatt P, K. V, Chaicumpa W. Role of Antisperm Antibodies in Infertility, Pregnancy, and Potential forContraceptive and Antifertility Vaccine Designs: Research Progress and Pioneering Vision

Sperm of humans, non-human primates, and other mammalian subjects is considered to be antigenic. The effect of changes in autoimmunity on reproductive cells such as spermatozoa and oocytes play a critical but indistinct role in fertility. Antisperm antibodies (ASAs) are invariably present in both females and males. However, the degree of ASA occurrence may vary according to individual and gender. Although the extent of infertility due to ASAs alone is yet to be determined, it has been found in almost 9-12% of patients who are infertile due to different causes. Postcoital presence of spermatozoa in the reproductive tract of women is not a contributory factor in ASA generation. However, ASA generation may be induced by trauma to the vaginal mucosa, or by anal or oral sex resulting in the deposition of sperm inside the digestive tract. It is strongly believed that, in humans and other species, at least some antibodies may bind to sperm antigens, causing infertility. This form of infertility is termed as immunological infertility, which may be accompanied by impairment of fertility, even in individuals with normozoospermia. Researchers target ASAs for two major reasons: (i) to elucidate the association between ASAs and infertility, the reason ASAs causes infertility, and the mechanism underlying ASA-mediated infertility; and (ii) to assess the potential of ASAs as a contraceptive in humans in case ASAs influences infertility. Therefore, this review explores the potential application of ASAs in the development of anti-spermatozoa vaccines for contraceptive purposes. The usefulness of ASAs for diagnosing obstructive azoospermia, salpingitis, and oligoasthenoteratozoospermia has been reviewed extensively. Important patents pertaining to potential candidates for spermatozoa-derived vaccines that may be utilized as contraceptives are discussed in depth. Antifertility vaccines, as well as treatments for ASA-related infertility, are also highlighted. This review will address many unresolved issues regarding mechanisms involving ASAs in the diagnosis, as well as prognoses, of male infertility. More documented scientific reports are cited to support the mechanisms underlying the potential role of ASA in infertility. The usefulness of sperm antigens or ASAs (recombinant) in human and wild or captive animal contraceptive vaccines has been revealed through research but is yet to be validated via clinical testing.

Complement alone drives efficacy of a chimeric antigonococcal monoclonal antibody

Multidrug-resistant Neisseria gonorrhoeae is a global health problem. Monoclonal antibody (mAb) 2C7 recognizes a gonococcal lipooligosaccharide epitope that is expressed by >95% of clinical isolates and hastens gonococcal vaginal clearance in mice. Chimeric mAb 2C7 (human immunoglobulin G1 [IgG1]) with an E430G Fc modification that enhances Fc:Fc interactions and hexamerization following surface-target binding and increases complement activation (HexaBody technology) showed significantly greater C1q engagement and C4 and C3 deposition compared to mAb 2C7 with wild-type Fc. Greater complement activation by 2C7-E430G Fc translated to increased bactericidal activity in vitro and, consequently, enhanced efficacy in mice, compared with “Fc-unmodified” chimeric 2C7. Gonococci bind the complement inhibitors factor H (FH) and C4b-binding protein (C4BP) in a human-specific manner, which dampens antibody (Ab)-mediated complement-dependent killing. The variant 2C7-E430G Fc overcame the barrier posed by these inhibitors in human FH/C4BP transgenic mice, for which a single 1 μg intravenous dose cleared established infection. Chlamydia frequently coexists with and exacerbates gonorrhea; 2C7-E430G Fc also proved effective against gonorrhea in gonorrhea/chlamydia-coinfected mice. Complement activation alone was necessary and sufficient for 2C7 function, evidenced by the fact that (1) “complement-inactive” Fc modifications that engaged Fc gamma receptor (FcγR) rendered 2C7 ineffective, nonetheless; (2) 2C7 was nonfunctional in C1q^−/− mice, when C5 function was blocked, or in C9^−/− mice; and (3) 2C7 remained effective in neutrophil-depleted mice and in mice treated with PMX205, a C5a receptor (C5aR1) inhibitor. We highlight the importance of complement activation for antigonococcal Ab function in the genital tract. Elucidating the correlates of protection against gonorrhea will inform the development of Ab-based gonococcal vaccines and immunotherapeutics.

A chimeric antibody that contains a "complement-enhancing" mutation in Fc (so-called HexaBody technology) shows increased bactericidal activity compared to antibody bearing wild-type Fc and may represent a promising immunotherapeutic approach against multidrug-resistant gonorrhea.

Immunity in the Cervix: Interphase between Immune and Cervical Epithelial Cells

The cervix is divided into two morphologically and immunologically distinct regions, namely, (1) the microbe-laden ectocervix, which is proximal to the vagina, and (2) the "sterile" endocervix, which is distal to the uterus. The two cervical regions are bordered by the cervical transformation zone (CTZ), an area of changing cells, and are predominantly composed of cervical epithelial cells. Epithelial cells are known to play a crucial role in the initiation, maintenance, and regulation of innate and adaptive response in collaboration with immune cells in several tissue types, including the cervix, and their dysfunction can lead to a spectrum of clinical syndromes. For instance, epithelial cells block progression and neutralize or kill microorganisms through multiple ways. These (ways) include mounting physical (intercellular junctions, secretion of mucus) and immune barriers (pathogen-recognition receptor-mediated pathways), which collectively and ultimately lead to the release of specific chemokines and or cytokines. The cytokines subsequently recruit subsets of immune cells appropriate to a particular immune context and response, such as dendritic cells (DCs), T, B, and natural killer (NK) cells. The immune response, as most biological processes in the female reproductive tract (FRT), is mainly regulated by estrogen and progesterone and their (immune cells) responses vary during different physiological phases of reproduction, such as menstrual cycle, pregnancy, and post menopause. The purpose of the present review is to compare the immunological profile of the mucosae and immune cells in the ecto- and endocervix and their interphase during the different phases of female reproduction.

Complement C3 opsonization of Chlamydia trachomatis facilitates uptake in human monocytes

Chlamydia trachomatis is an obligate intracellular bacterium that causes severe infections, which can lead to infertility and ectopic pregnancy. Although both innate and adaptive immune responses are elicited during chlamydial infection the bacterium succeeds to evade host defense mechanisms establishing chronic infections. Thus, studying the host-pathogen interaction during chlamydial infection is of importance to understand how C. trachomatis can cause chronic infections. Both the complement system and monocytes play essential roles in anti-bacterial defense, and, therefore, we investigated the interaction between the complement system and the human pathogens C. trachomatis D and L2. Complement competent serum facilitated rapid uptake of both chlamydial serovars into monocytes. Using immunoelectron microscopy, we showed that products of complement C3 were loosely deposited on the bacterial surface in complement competent serum and further characterization demonstrated that the deposited C3 product was the opsonin iC3b. Using C3-depleted serum we confirmed that complement C3 facilitates rapid uptake of chlamydiae into monocytes in complement competent serum. Complement facilitated uptake did not influence intracellular survival of C. trachomatis or C. trachomatis-induced cytokine secretion. Hence, C. trachomatis D and L2 activate the complement system leading to chlamydial opsonization by iC3b and subsequent phagocytosis, activation and bacterial elimination by human monocytes.

MetQ of Neisseria gonorrhoeae Is a Surface-Expressed Antigen That Elicits Bactericidal and Functional Blocking Antibodies

Neisseria gonorrhoeae, the causative agent of the sexually transmitted infection (STI) gonorrhea, is a growing public health threat for which a vaccine is urgently needed. We characterized the functional role of the gonococcal MetQ protein, which is the methionine binding component of an ABC transporter system, and assessed its potential as a candidate antigen for inclusion in a gonococcal vaccine. MetQ has been found to be highly conserved in all strains investigated to date, it is localized on the bacterial surface, and it binds l-methionine with a high affinity. MetQ is also involved in gonococcal adherence to cervical epithelial cells. Mutants lacking MetQ have impaired survival in human monocytes, macrophages, and serum. Furthermore, antibodies raised against MetQ are bactericidal and are able to block gonococcal adherence to epithelial cells. These data suggest that MetQ elicits both bactericidal and functional blocking antibodies and is a valid candidate antigen for additional investigation and possible inclusion in a vaccine for prevention of gonorrhea.

The mucosal immune system of fish: the evolution of tolerating commensals while fighting pathogens

The field of mucosal immunology research has grown fast over the past few years, and our understanding on how mucosal surfaces respond to complex antigenic cocktails is expanding tremendously. With the advent of new molecular sequencing techniques, it is easier to understand how the immune system of vertebrates is, to a great extent, orchestrated by the complex microbial communities that live in symbiosis with their hosts. The commensal microbiota is now seen as the "extended self" by many scientists. Similarly, fish immunologist are devoting important research efforts to the field of mucosal immunity and commensals. Recent breakthroughs on our understanding of mucosal immune responses in teleost fish open up the potential of teleosts as animal research models for the study of human mucosal diseases. Additionally, this new knowledge places immunologists in a better position to specifically target the fish mucosal immune system while rationally designing mucosal vaccines and other immunotherapies. In this review, an updated view on how teleost skin, gills and gut immune cells and molecules, function in response to pathogens and commensals is provided. Finally, some of the future avenues that the field of fish mucosal immunity may follow in the next years are highlighted.

Structure-function studies of the Neisseria gonorrhoeae major outer membrane porin

The major outer membrane porin (PorB) expressed by Neisseria gonorrhoeae plays multiple roles during infection, in addition to its function as an outer membrane pore. We have generated a panel of mutants of N. gonorrhoeae strain FA1090 expressing a variety of mutant porB genes that all function as porins. We identified multiple regions of porin that are involved in its binding to the complement regulatory factors C4b-binding protein and factor H and confirmed that the ability to bind at least one factor is required for FA1090 to survive the bactericidal effects of human serum. We tested the ability of these mutants to inhibit both apoptosis and the oxidative burst in polymorphonuclear leukocytes but were unable to identify the porin domains required for either function. This study has identified nonessential porin domains and some potentially essential portions of the protein and has further expanded our understanding of the contribution of the porin domains required for complement regulation.

Michael F, Stupak J, Lewis LA, Ram S, Rice PA. Immunization against a saccharide epitope accelerates clearance of experimental gonococcal infection

The emergence of ceftriaxone-resistant strains of Neisseria gonorrhoeae may herald an era of untreatable gonorrhea. Vaccines against this infection are urgently needed. The 2C7 epitope is a conserved oligosaccharide (OS) structure, a part of lipooligosaccharide (LOS) on N gonorrhoeae. The epitope is expressed by 94% of gonococci that reside in the human genital tract (in vivo) and by 95% of first passaged isolates. Absence of the 2C7 epitope shortens the time of gonococcal carriage in a mouse model of genital infection. To circumvent the limitations of saccharide immunogens in producing long lived immune responses, previously we developed a peptide mimic (called PEP1) as an immunologic surrogate of the 2C7-OS epitope and reconfigured it into a multi-antigenic peptide, (MAP1). To test vaccine efficacy of MAP1, female BALB/c mice were passively immunized with a complement-dependent bactericidal monoclonal antibody specific for the 2C7 epitope or were actively immunized with MAP1. Mice immunized with MAP1 developed a TH1-biased anti-LOS IgG antibody response that was also bactericidal. Length of carriage was shortened in immune mice; clearance occurred in 4 days in mice passively administered 2C7 antibody vs. 6 days in mice administered control IgG3λ mAb in one experiment (p = 0.03) and 6 vs. 9 days in a replicate experiment (p = 0.008). Mice vaccinated with MAP1 cleared infection in 5 days vs. 9 days in mice immunized with control peptide (p = 0.0001 and p = 0.0002, respectively in two replicate experiments). Bacterial burden was lower over the course of infection in passively immunized vs. control mice in both experiments (p = 0.008 and p = 0.0005); burdens were also lower in MAP1 immunized mice vs. controls (p<0.0001) and were inversely related to vaccine antibodies induced in the vagina (p = 0.043). The OS epitope defined by mAb 2C7 may represent an effective vaccine target against gonorrhea, which is rapidly becoming incurable with currently available antibiotics.

The N-linked carbohydrate moiety of male reproductive tract CD52 (mrt-CD52) interferes with the complement system via binding to C1q

Antisperm antibody detected in infertile female patients' sera has been shown to correlate with reduced fertility. The antibody showed strong complement-dependent cytotoxicity as determined by the sperm immobilization test (SIT). CD52 is a human glycosylphosphatidylinositol (GPI)-anchored antigen present in lymphocytes and male reproductive tracts (mrt), including mature sperm and seminal plasma. Recently, purified mrt-CD52 from human seminal plasma has been reported to interfere with the classical complement pathway, but not lectin binding or alternative pathways of the complement system. The purpose of this study is to determine which stage of the classical pathway mrt-CD52 regulates. mrt-CD52 was purified from human seminal plasma or intact sperm membrane. Immunoprecipitation assay was performed with the reaction of mrt-CD52, human complement and mAb H6-3C4. Immunoprecipitate was formed by the carbohydrate moiety of mrt-CD52, but not by the GPI-anchor peptide. The C1q molecule (29 kDa) was detected in the immunoprecipitates by Western blotting analysis probed with anti C1q antibody, indicating that the carbohydrate moiety of mrt-CD52 binds to C1q. Also, the complement-dependent SIT revealed that purified CD52 inhibited sperm immobilization activity by antisperm antibody. These results suggest that mrt-CD52 protects sperm function from complement attack if antisperm antibody is generated in the female reproductive tracts.

Properdin is critical for antibody-dependent bactericidal activity against Neisseria gonorrhoeae that recruit C4b-binding protein

Gonorrhea, a sexually transmitted disease caused by Neisseria gonorrhoeae, is an important cause of morbidity worldwide. A safe and effective vaccine against gonorrhea is needed because of emerging resistance of gonococci to almost every class of antibiotic. A gonococcal lipooligosaccharide epitope defined by the mAb 2C7 is being evaluated as a candidate for development of an Ab-based vaccine. Immune Abs against N. gonorrhoeae need to overcome several subversive mechanisms whereby gonococcus evades complement, including binding to C4b-binding protein (C4BP; classical pathway inhibitor) and factor H (alternative pathway [AP] inhibitor). The role of AP recruitment and, in particular, properdin in assisting killing of gonococci by specific Abs is the subject of this study. We show that only those gonococcal strains that bind C4BP require properdin for killing by 2C7, whereas strains that do not bind C4BP are efficiently killed by 2C7 even when AP function is blocked. C3 deposition on bacteria mirrored killing. Recruitment of the AP by mAb 2C7, as measured by factor B binding, occurred in a properdin-dependent manner. These findings were confirmed using isogenic mutant strains that differed in their ability to bind to C4BP. Immune human serum that contained bactericidal Abs directed against the 2C7 lipooligosaccharide epitope as well as murine antigonococcal antiserum required functional properdin to kill C4BP-binding strains, but not C4BP-nonbinding strains. Collectively, these data point to an important role for properdin in facilitating immune Ab-mediated complement-dependent killing of gonococcal strains that inhibit the classical pathway by recruiting C4BP.

Molecular characterization of the interaction between sialylated Neisseria gonorrhoeae and factor H

Human factor H (HufH), a key inhibitor of the alternative pathway of complement, binds to Neisseria gonorrhoeae and constitutes an important mechanism of human-specific complement evasion. The C-terminal domain 20 of HufH contains the binding site for sialylated gonococci. We exploited differences in amino acid sequences between human and non-binding chimpanzee fH domain 20 to create cross-species mutations to define amino acids important for binding to sialylated gonococci. We used fH/Fc fusion constructs that contained contiguous fH domains 18-20 fused to Fc fragments of murine IgG2a. The Fc region was used both as a tag for detection of each fusion molecule on the bacterial surface and as an indicator for complement-dependent killing. Arg-1203 was critical for binding to both porin (Por) B.1A and PorB.1B strains. Modeling of the R1203N human-to-chimpanzee mutation using the crystal structure of HufH19-20 as a template showed a loss of positive charge that protrudes at the C terminus of domain 20. We tested the functional importance of Arg-1203 by incubating sialylated gonococci with normal human serum, in the presence of wild-type HufH18-20/Fc or its R1203A mutant. Gonococci bound and were killed by wild-type HufH18-20/Fc but not by the R1203A mutant. A recombinant fH/Fc molecule that contained chimpanzee domain 20, humanized only at amino acid 1203 (N1203R) also bound to sialylated gonococci and restored killing. These findings provide further insights into the species specificity of gonococcal infections and proof-of-concept of a novel therapeutic approach against gonorrhea, a disease rapidly becoming resistant to conventional antibiotics.

Contribution of interactions between complement inhibitor C4b-binding protein and pathogens to their ability to establish infection with particular emphasis on Neisseria gonorrhoeae

Complement activation and resulting opsonisation with C3b form key arms of the innate immune defense against infections. However, a wide variety of pathogens subvert complement attack by binding host complement inhibitors, which results in diminished opsonophagocytosis and killing of bacteria by lysis. Human C4b-binding protein (C4BP) binds Neisseria gonorrhoeae and Streptococcus pyogenes, both uniquely human pathogens. This binding specificity is circumvented by other bacterial species, which bind C4BP from numerous mammalian hosts that they infect. Binding of C4BP to Neisseria is mediated by outer membrane porin proteins and appears to be one of the main factors mediating serum resistance. Targeting C4BP binding sites on bacterial surfaces with vaccine-induced antibodies may block binding of C4BP and enhance a common vaccine design strategy that depends on the generation of complement-dependent bactericidal and opsonophagocytic antibody activities.

The role of complement in gonococcal infection of cervical epithelia

Neisseria gonorrhoeae is an exclusive human pathogen that causes the sexually transmitted disease, gonorrhea. The gonococcus has developed an exquisite repertoire of mechanisms by which it is able to evade host innate and adaptive immune responses. Our previous data indicate that the predominately asymptomatic nature ofgonococcal cervicitis may, in part, be attributed to the ability of these bacteria to subvert the normal function of complement to promote cervical disease. Herein we describe the interaction of N. gonorrhoeae with the complement alternative pathway with a particular focus on the importance of this interaction in promoting gonococcal cervicitis.

Human factor H interacts selectively with Neisseria gonorrhoeae and results in species-specific complement evasion

Complement forms a key arm of innate immune defenses against gonococcal infection. Sialylation of gonococcal lipo-oligosaccharide, or expression of porin 1A (Por1A) protein, enables Neisseria gonorrhoeae to bind the alternative pathway complement inhibitor, factor H (fH), and evade killing by human complement. Using recombinant fH fragment-murine Fc fusion proteins, we localized two N. gonorrhoeae Por1A-binding regions in fH: one in complement control protein domain 6, the other in complement control proteins 18-20. The latter is similar to that reported previously for sialylated Por1B gonococci. Upon incubation with human serum, Por1A and sialylated Por1B strains bound full-length human fH (HufH) and fH-related protein 1. In addition, Por1A strains bound fH-like protein 1 weakly. Only HufH, but not fH from other primates, bound directly to gonococci. Consistent with direct HufH binding, unsialylated Por1A gonococci resisted killing only by human complement, but not complement from other primates, rodents or lagomorphs; adding HufH to these heterologous sera restored serum resistance. Lipo-oligosaccharide sialylation of N. gonorrhoeae resulted in classical pathway regulation as evidenced by decreased C4 binding in human, chimpanzee, and rhesus serum but was accompanied by serum resistance only in human and chimpanzee serum. Direct-binding specificity of HufH only to gonococci that prevents serum killing is restricted to humans and may in part explain species-specific restriction of natural gonococcal infection. Our findings may help to improve animal models for gonorrhea while also having implications in the choice of complement sources to evaluate neisserial vaccine candidates.

Molecular characterization of the interaction between porins of Neisseria gonorrhoeae and C4b-binding protein

Neisseria gonorrhoeae, the causative agent of gonorrhea, is a natural infection only in humans. The resistance of N. gonorrhoeae to normal human serum killing correlates with porin (Por)-mediated binding to the complement inhibitor, C4b-binding protein (C4BP). The entire binding site for both porin molecules resides within complement control protein domain 1 (CCP1) of C4BP. Only human and chimpanzee C4BPs bind to Por1B-bearing gonococci, whereas only human C4BP binds to Por1A strains. We have now used these species-specific differences in C4BP binding to gonococci to map the porin binding sites on CCP1 of C4BP. A comparison between human and chimpanzee or rhesus C4BP CCP1 revealed differences at 4 and 12 amino acid positions, respectively. These amino acids were targeted in the construction of 13 recombinant human mutant C4BPs. Overall, amino acids T43, T45, and K24 individually and A12, M14, R22, and L34 together were important for binding to Por1A strains. Altering D15 (found in man) to N15 (found in rhesus) introduced a glycosylation site that blocked binding to Por1A gonococci. C4BP binding to Por1B strains required K24 and was partially shielded by additional glycosylation in the D15N mutant. Only those recombinant mutant C4BPs that bound to bacteria rescued them from 100% killing by rhesus serum, thereby providing a functional correlate for the binding studies and highlighting C4BP function in gonococcal serum resistance.

Antisperm antibodies and conception

Sperm have been known to be antigenic for more than a century. There is a strong body of evidence that in humans and in other species at least some antibodies that bind to sperm antigens can cause infertility. Therefore, these antibodies are of interest today for two practical reasons. Firstly, the association of the antibodies with infertility means that they must be detected and then the couples treated appropriately. Secondly, because these antibodies can induce infertility they have the potential to be developed for contraceptive purposes in humans and also for the control of feral animal populations.

Complement and complement regulators in the male reproductive system

Spermatozoa are almost unique among cells in that they must survive transplantation into a foreign host in order to perform their physiological role. The biggest hurdle to overcome is innate immune defence that will target the invaders in the female genital tract. Complement is a major player in innate immunity and is present in the female genital tract. Spermatozoa must therefore evade complement attack if they are to reach their goal. Complement evasion is achieved by the presence of complement regulators both in seminal plasma and on the spermatozoa. Here we discuss the parts played by complement and complement regulators in permitting spermatozoa to survive long enough to reach the oocyte, in clearance of the excess spermatozoa that have outlived their usefulness and in aiding activation of spermatozoa to engage the oocyte. In particular, we focus on the unique distribution patterns of complement regulators on spermatozoa, patterns that strongly suggest roles in spermatozoal development and oocyte binding. An understanding of these roles will inform studies of their contribution to fertility and infertility in man.

Enhanced factor H binding to sialylated Gonococci is restricted to the sialylated lacto-N-neotetraose lipooligosaccharide species: implications for serum resistance and evidence for a bifunctional lipooligosaccharide sialyltransferase in Gonococci

We isolated serologically identical (by serovar determination and porin variable region [VR] typing) strains of Neisseria gonorrhoeae from an infected male and two of his monogamous female sex partners. One strain (termed 398078) expressed the L1 (Galalpha1 --> 4 [corrected] Galbeta1 --> 4Glcbeta1 --> 4HepI) lipooligosaccharide (LOS) structure exclusively; the other (termed 398079) expressed the lacto-N-neotetraose (LNT; Galbeta1 --> 4GlcNAcbeta1 --> 3Galbeta1 --> 4Glcbeta1 --> 4HepI) LOS structure. The strain from the male index case expressed both glycoforms and exhibited both immunotypes. Nuclear magnetic resonance analysis revealed that sialic acid linked to the terminal Gal of L1 LOS via an alpha2 --> 6 linkage and, as expected, to the terminal Gal of LNT LOS via an alpha2--> 3 linkage. Insertional inactivation of the sialyltransferase gene (known to sialylate LNT LOS) abrogated both L1 LOS sialylation and LNT LOS sialylation, suggesting a bifunctional nature of this enzyme in gonococci. Akin to our previous observations, sialylation of the LNT LOS of strain 398079 enhanced the binding of the complement regulatory molecule, factor H. Rather surprisingly, factor H did not bind to sialylated strain 398078. LOS sialylation conferred the LNT LOS-bearing strain complete (100%) resistance to killing by even 50% nonimmune normal human serum (NHS), whereas sialylation of L1 LOS conferred resistance only to 10% NHS. The ability of gonococcal sialylated LNT to bind factor H confers high-level serum resistance, which is not seen with sialylated L1 LOS. Thus, serum resistance mediated by sialylation of gonococcal L1 and LNT LOS occurs by different mechanisms, and specificity of factor H binding to sialylated gonococci is restricted to the LNT LOS species.

Human C4b-binding protein selectively interacts with Neisseria gonorrhoeae and results in species-specific infection

Neisseria gonorrhoeae is the causative agent of gonorrhea, a disease that is restricted to humans. Complement forms a key arm of the innate immune system that combats gonococcal infections. N. gonorrhoeae uses its outer membrane porin (Por) molecules to bind the classical pathway of complement down-regulatory protein C4b-binding protein (C4bp) to evade killing by human complement. Strains of N. gonorrhoeae that resisted killing by human serum complement were killed by serum from rodent, lagomorph, and primate species, which cannot be readily infected experimentally with this organism and whose C4bp molecules did not bind to N. gonorrhoeae. In contrast, we found that Yersinia pestis, an organism that can infect virtually all mammals, bound species-specific C4bp and uniformly resisted serum complement-mediated killing by these species. Serum resistance of gonococci was restored in these sera by human C4bp. An exception was serotype Por1B-bearing gonococcal strains that previously had been used successfully in a chimpanzee model of gonorrhea that simulates human disease. Por1B gonococci bound chimpanzee C4bp and resisted killing by chimpanzee serum, providing insight into the host restriction of gonorrhea and addressing why Por1B strains, but not Por1A strains, have been successful in experimental chimpanzee infection. Our findings may lead to the development of better animal models for gonorrhea and may also have implications in the choice of complement sources to evaluate neisserial vaccine candidates.

Antigenic epitope for sperm-immobilizing antibody detected in infertile women

CD52 is a glycosylphosphatidylinositol (GPI) anchor protein occurring in lymphocytes, the epididymis, seminal plasma and on ejaculated sperm surface. The molecular structure of male reproductive tract CD52 (mrtCD52) is quite different from that of lymphocyte CD52 except for a peptide sequence comprising 12 amino acids. The carbohydrate molecule may thus provide antigenic epitopes to females. The repeated N-acetyllactosamine units of the N-linked carbohydrate present in the mrtCD52 were identified as a pathogenic antigen for infertility using a monoclonal antibody (MAb H6-3C4) generated from an infertile patient's peripheral blood lymphocyte. We suggested also the possible presence of O-linked carbohydrate in human mrtCD52, although it is not known whether this carbohydrate is immunogenic or not. This article gives an overview of the structure and function of mrtCD52 as well as the fertilization-blocking mechanism of the antibody against this molecule.

Intranasal administration of recombinant Neisseria gonorrhoeae transferrin binding proteins A and B conjugated to the cholera toxin B subunit induces systemic and vaginal antibodies in mice

The transferrin binding proteins (TbpA and TbpB) comprise the gonococcal transferrin receptor and are considered potential antigens for inclusion in a vaccine against Neisseria gonorrhoeae. Intranasal (IN) immunization has shown promise in development of immunity against sexually transmitted disease pathogens, in part due to the induction of antigen-specific genital tract immunoglobulin A (IgA) and IgG. Conjugation of antigens to the highly immunogenic cholera toxin B subunit (Ctb) enhances antibody responses in the serum and mucosal secretions following IN vaccination. In the current study, we characterized the anti-Tbp immune responses following immunization of mice IN with recombinant transferrin binding proteins (rTbpA and rTbpB) conjugated to rCtb. We found that both rTbpA-Ctb and rTbpB-Ctb conjugates administered IN induced antibody responses in the serum and genital tract. IN immunization resulted in both IgA and IgG in the genital tract; however, subcutaneous immunization mainly generated IgG. Surprisingly, rTbpA alone was immunogenic and induced serum and mucosal antibody responses similar to those elicited against the rTbpA-Ctb conjugate. Overall, rTbpB was much more immunogenic than rTbpA, generating serum IgG levels that were greater than those elicited against rTbpA. Bactericidal assays conducted with sera collected from mice immunized IN with TbpA and/or TbpB indicated that both antigens generated antibodies with bactericidal activity. Anti-TbpA antibodies were cross-bactericidal against heterologous gonococcal strains, whereas TbpB-specific antibodies were less cross-reactive. By contrast, antibodies elicited via subcutaneous immunization were not cross-bactericidal against heterologous strains, indicating that IN vaccination could be the preferred route for elicitation of biologically functional antibodies.

The molecular mechanisms used by Neisseria gonorrhoeae to initiate infection differ between men and women

The molecular mechanisms used by the gonococcus to initiate infection exhibit gender specificity. The clinical presentations of disease are also strikingly different upon comparison of gonococcal urethritis to gonococcal cervicitis. An intimate association occurs between the gonococcus and the urethral epithelium and is mediated by the asialoglycoprotein receptor. Gonococcal interaction with the urethral epithelia cell triggers cytokine release, which promotes neutrophil influx and an inflammatory response. Similarly, gonococcal infection of the upper female genital tract also results in inflammation. Gonococci invade the nonciliated epithelia, and the ciliated cells are subjected to the cytotoxic effects of tumor necrosis factor alpha induced by gonococcal peptidoglycan and lipooligosaccharide. In contrast, gonococcal infection of the lower female genital tract is typically asymptomatic. This is in part the result of the ability of the gonococcus to subvert the alternative pathway of complement present in the lower female genital tract. Gonococcal engagement of complement receptor 3 on the cervical epithelia results in membrane ruffling and does not promote inflammation. A model of gonococcal pathogenesis is presented in the context of the male and female human urogenital tracts.

Clinical associations and mechanisms of action of antisperm antibodies

OBJECTIVE

To review and critique the current English literature describing the effects of antisperm antibodies (ASA) on mammalian fertility.

DESIGN

A comprehensive English language literature was searched using Medline and by hand-searching. Emphasis was placed on clinically relevant articles.

RESULT(S)

Results from the studies were extrapolated and the effects of ASA on fertility described.

CONCLUSION(S)

Antisperm antibodies may interfere with fertility. Not all ASA cause infertility. Current tests cannot differentiate the infertility-related ASA from those that do not interfere with infertility, because the antigenic specificities of these ASA are not known. The antigens which the infertility-related ASA must be characterized to allow an accurate detection and proper treatment for couples with ASA.

The role of lipooligosaccharide in Neisseria gonorrhoeae pathogenesis of cervical epithelia: lipid A serves as a C3 acceptor molecule

The use of primary, human, ecto- and endocervical epithelial cell cultures has increased our understanding of the pathogenesis of gonococcal infection in women. Primary cervical epithelial cells express complement (C') receptor type 3 (CR3) and C' proteins required for alternative pathway (AP) activity. Gonococcus -induced membrane ruffling and cellular invasion of primary cervical epithelia is mediated by CR3 and requires co-operative CR3 binding by gonococcus-bound iC3b, porin and pilus. We have extended these studies to identify the site of C3 deposition upon gonococci within the cervical microenvironment. By immunoprecipitation and ELISA we demonstrate that covalent and non-covalent associations occurred between gonococcal LOS and C' protein C3. Sialylation or LOS truncation did not alter the gonococcus-CR3 interaction. By Western blot analysis we observed comparable C3 opsonization patterns among a panel of LOS truncation mutants, sialylated wild-type gonococci, or wild-type bacteria that were not sialylated. Quantitative association/invasion assays performed in the presence or absence of LOS competimers support C3b deposition on the lipid A core structure. Our findings demonstrate a role for lipid A as a C3 acceptor site and suggest that multiple factors govern C3b deposition and its subsequent conversion to iC3b on the surface of the gonococcus within the cervical microenvironment.

A co-operative interaction between Neisseria gonorrhoeae and complement receptor 3 mediates infection of primary cervical epithelial cells

Little is known about the pathogenesis of gonococcal infection within the lower female genital tract. We recently described the distribution of complement receptor 3 (CR3) on epithelia of the female genital tract. Our studies further indicate that CR3-mediated endocytosis serves as a primary mechanism by which N. gonorrhoeae elicits membrane ruffling and cellular invasion of primary, human, cervical epithelial cells. We have extended these studies to describe the nature of the gonococcus-CR3 interaction. Western Blot analysis demonstrated production of alternative pathway complement components by ecto- and endocervical cells which allows C3b deposition on gonococci and its rapid conversion to iC3b. Anti-iC3b and -factor I antibodies significantly inhibited adherence and invasion of primary cervical cells, suggesting that iC3b covalently bound to the gonococcus serves as a primary ligand for CR3 adherence. However, gonococcal porin and pili also bound to the I-domain of CR3 in a non-opsonic manner. Binding of porin and pili to CR3 were required for adherence to and invasion of cervical epithelia. Collectively, these data suggest that gonococcal adherence to CR3 occurs in a co-operative manner, which requires gonococcal iC3b-opsonization, porin and pilus. In conjunction, these molecules facilitate targeting to and successful infection of the cervical epithelium.

Characterization of glycosylphosphatidylinositol-anchored decay accelerating factor (GPI-DAF) and transmembrane DAF gene expression in wild-type and GPI-DAF gene knockout mice using polyclonal and monoclonal antibodies with dual or single specificity

Decay-accelerating factor (DAF, CD55) is a glycosylphosphatidylinositol (GPI)-linked membrane inhibitor of complement activation. While human and other mammalian species contain only one DAF gene, two distinct DAF genes, referred to as GPI-DAF and transmembrane (TM)-DAF, respectively, have been identified in the mouse. Using several independently generated monoclonal and polyclonal antibodies, either with dual or single specificity for GPI-DAF and TM-DAF gene products, we have examined the expression of the two DAF genes in tissues of the wild-type and a strain of knockout mouse whose GPI-DAF gene has been inactivated. By fluorescence-activated cell sorting (FACS) analysis, we found that DAF protein is present on the wild-type mouse erythrocytes and lymphocytes but no signal was detectable on the same cells of GPI-DAF gene knockout mice. Both T and B lymphocytes and splenic macrophages express the GPI-DAF gene but the expression level is higher on B lymphocytes than on T lymphocytes. Within the T cell population, both CD4+ and CD8+ T cells are positive. DAF protein was detected by immunohistochemistry at high levels on wild-type mouse spermatids and mature sperm. In contrast, only mature sperm stained positive in the GPI-DAF gene knockout mouse testis, suggesting that GPI-DAF but not the TM-DAF gene is expressed on spermatids. Examination of the fetoplacental unit at the day 7.5 stage revealed that GPI-DAF but not the TM-DAF gene is expressed in the maternal decidua cells surrounding the trophoectoderm of the embryo. No DAF expression was detected on trophoblast or the embryo proper. These findings suggest that although the TM-DAF gene is irrelevant on mouse blood cells, the two DAF genes may have different roles in germ cell development and/or mature sperm function. Because complement receptor 1-related gene/protein y (Crry) has been shown to be expressed on early mouse embryos, the complete lack of GPI-DAF and TM-DAF gene expression in early mouse development may explain the observed sensitivity of Crry-deficient embryos to maternal complement attack.

The role of complement receptor 3 (CR3) in Neisseria gonorrhoeae infection of human cervical epithelia

Neisseria gonorrhoeae is an important sexually transmitted pathogen and a major cofactor in HIV-1 infection. This organism uses different mechanisms to infect male and female genital tract epithelia. Receptor-mediated endocytosis of N. gonorrhoeae is the principle mechanism of entry into male urethral epithelial cells. Infection in men leads to a pronounced inflammatory response. In contrast, N. gonorrhoeae infection in women induces ruffling of the cervical epithelia, allowing a macropinocytic mechanism of entry. Infection in women is frequently asymptomatic, suggesting suppression of the inflammatory response. N. gonorrhoeae-induced membrane ruffling and inflammation suppression are consistent with the ability of this bacterium to enter cervical epithelial cells, in vitro and in vivo, by interaction with complement receptor 3 (CR3), a receptor that does not trigger an inflammatory response. This receptor is present on cervical epithelial cells but not on male urogenital tract epithelia. N. gonorrhoeae engagement of CR3 initiates a unique mechanism of bacterial-induced membrane ruffling and internalization. These studies explain why the pathology of N. gonorrhoeae infection differs between males and females. Additionally, the observation that this receptor is present on cervical epithelia may provide insight into the pathogenesis of other sexually transmitted pathogens.

C4bp binding to porin mediates stable serum resistance of Neisseria gonorrhoeae

Screening of 29 strains of Neisseria gonorrhoeae revealed that 16/21 serum resistant strains and 0/8 serum sensitive strains bound C4bp, suggesting that C4bp binding to gonococci could contribute to serum resistance. C4bp bound to gonococci retained cofactor (C4b-degrading) function. Using allelic exchange to construct strains with hybrid Por1A/B molecules, we demonstrate that the N-terminal loop (loop 1) of Por1A is required for C4bp binding. Serum resistant Por1B gonococcal strains also bind C4bp via their Por molecule. Using allelic exchange and site-directed mutagenesis, we have shown that loops 5 and 7 together form a negatively charged C4bp binding domain. C4bp-Por1B interactions are ionic in nature (inhibited by high salt as well as by heparin), while the C4bp-Por1A bond is hydrophobic. mAbs directed against SCR1 of the alpha-chain of C4bp inhibit C4bp binding to both Por1A and Por1B. Furthermore, only recombinant C4bp mutant molecules that contain alpha-chain SCR1 bind both Por1A and Por1B gonococci, confirming that SCR1 contains Por binding sites. C4bp alpha-chain monomers do not bind strains with either Por molecule, suggesting that the polymeric form of C4bp is required for binding to gonococci. Inhibition of C4bp binding to serum resistant Por1A and Por1B strains in a serum bactericidal assay using fAb fragments against C4bp SCR1 results in complete killing at 30 min of otherwise fully serum resistant strains in only 10% normal serum, underscoring the role of C4bp in mediating gonococcal serum resistance.

Binding of C4b-binding protein to porin: a molecular mechanism of serum resistance of Neisseria gonorrhoeae

We screened 29 strains of Neisseria gonorrhoeae and found 16/21 strains that resisted killing by normal human serum and 0/8 serum sensitive strains that bound the complement regulator, C4b-binding protein (C4bp). Microbial surface-bound C4bp demonstrated cofactor activity. We constructed gonococcal strains with hybrid porin (Por) molecules derived from each of the major serogroups (Por1A and Por1B) of N. gonorrhoeae, and showed that the loop 1 of Por1A is required for C4bp binding. Por1B loops 5 and 7 of serum-resistant gonococci together formed a negatively charged C4bp-binding domain. C4bp-Por1B interactions were ionic in nature (inhibited by high salt or by heparin), whereas the C4bp-Por1A bond was hydrophobic. Only recombinant C4bp mutant molecules containing the NH2-terminal alpha-chain short consensus repeat (SCR1) bound to both Por1A and Por1B gonococci, suggesting that SCR1 contained Por binding sites. C4bp alpha-chain monomers did not bind gonococci, indicating that the polymeric form of C4bp was required for binding. Using fAb fragments against C4bp SCR1, C4bp binding to Por1A and Por1B strains was inhibited in a complement-dependent serum bactericidal assay. This resulted in complete killing of these otherwise fully serum resistant strains in only 10% normal serum, underscoring the importance of C4bp in mediating gonococcal serum resistance.

Identification and functional characterization of a new gene encoding the mouse terminal complement inhibitor CD59

CD59 is a 18- to 20-kDa, GPI-anchored membrane protein that functions as a key regulator of the terminal step of the complement activation cascade. It restricts binding of C9 to the C5b-8 complex, thereby preventing the formation of the membrane attack complex (C5b-9 of complement). A single human CD59 gene has been identified, and corresponding genetic homologues from rat, mouse, and pig have been characterized in previous studies. In this study, we report the discovery and functional characterization of a separate cd59 gene in the mouse (referred to as cd59b, the previously characterized mouse cd59 gene as cd59a). Mouse cd59b is 85% and 63% identical to cd59a at the nucleotide and amino acid level, respectively. In cDNA transfection experiments with Chinese hamster ovary cells, peptide-tagged cd59b was detected on the cell surface by flow cytometry and was shown to be susceptible to phosphatidylinositol-specific phospholipase C cleavage. Chinese hamster ovary cells expressing cd59b were significantly more resistant than control cells to human and mouse complement-mediated lysis. These results suggest that cd59b encodes a GPI-anchored protein that is functionally active as a membrane attack complex inhibitor. Northern blot analysis revealed that cd59b is expressed selectively in the mouse testis. In contrast, the major transcript of cd59a was shown to be expressed at high levels in the heart, kidney, liver, and lung, but only minimally in the testis. These results revealed the existence of two distinct cd59 genes in the mouse that are differentially regulated and that may have nonoverlapping physiological functions in vivo.

Vaccine for contraception targeting sperm

Development of a vaccine(s) based on sperm antigens represents a promising approach to contraception. The utility of a sperm antigen in immunocontraception is contingent upon its tissue specificity, involvement in fertility and on raising high antibody titer, especially locally in the genital tract, that is capable of inducing reversible infertility. Several sperm antigens, such as lactate dehydrogenase C4, PH-20, sperm protein (SP)-10, fertilization antigen (FA)-1, FA-2, cleavage signal (CS)-1, NZ-1, and NZ-2 have been proposed as potential candidates for the vaccine development. Spermzona pellucida (ZP) binding is a pivotal tissue- and mostly species-specific event in the fertilization process, and the molecules involved in this site constitute the most exciting candidates for immuno-contraception. FA-1 is a sperm-specific glycoprotein having receptor activity for ZP recognition and binding. Complementary DNA encoding for FA-1 antigen has been cloned and sequenced. Active immunization of animals with recombinant FA-1 antigen causes a long-lasting reversible inhibition in fertility by raising a sperm-specific immune response. This antigen is also involved in human immunoinfertility. The exciting findings from the recent trial in immunoinfertile couples indicate that the FA-1 antigen may have clinical application in the treatment of male infertility. A vaccine having most appropriate tissue-specific and effective recombinant and/or synthetic epitopes of various sperm antigens, such as the FA-1 antigen, in a single formulation may provide a highly immunogenic and efficacious antisperm vaccine for contraception. The advances made during the last 5 years suggest that it may be a realistic proposition.

Invasion of human mucosal epithelial cells by Neisseria gonorrhoeae upregulates expression of intercellular adhesion molecule 1 (ICAM-1)

Infection of the mucosa by Neisseria gonorrhoeae involves adherence to and invasion of epithelial cells. Little is known, however, about the expression by mucosal epithelial cells of molecules that mediate cellular interactions between epithelial cells and neutrophils at the site of gonococcal infection. The aim of this study was to determine the expression of intercellular adhesion molecule 1 (ICAM-1) by epithelial cells during the process of gonococcal invasion. The highly invasive strain FA1090 and the poorly invasive strain MS11 were incubated with human endometrial adenocarcinoma (HEC-1-B) or human cervical carcinoma (ME-180) epithelial cells, after which ICAM-1 expression was measured by flow cytometry. After 15 h of infection with FA1090, expression of ICAM-1 increased 4.7- and 2.1-fold for HEC-1-B and ME-180 cells, respectively, whereas 15 h of infection of HEC-1-B cells with MS11 increased ICAM-1 expression only 1.6-fold. ICAM-1 expression was restricted to the cell surface, since no soluble ICAM-1 was detected. The distribution of staining was heterogeneous and mimicked that seen after treatment of HEC-1-B cells with the ICAM-1 agonist tumor necrosis factor alpha (TNF-alpha) in the absence of bacteria. PCR and dot blot analyses of ICAM-1 mRNA showed no change in levels over time in response to infection. Although TNF-alpha was produced by HEC-1-B cells after infection, the extent of ICAM-1 upregulation was not affected by neutralizing anti-TNF-alpha antiserum. Dual-fluorescence flow cytometry showed that the cells with the highest levels of ICAM-1 expression were cells with associated gonococci. We conclude that epithelial cells upregulate the expression of ICAM-1 in response to infection with invasive gonococci. On the mucosa, upregulation of ICAM-1 by infected epithelial cells may function to maintain neutrophils at the site of infection, thereby reducing further invasion of the mucosa by gonococci.

Modulation of integrin function inhibits HIV transmission to epithelial cells and fertilization

Integrin-mediated adhesive interactions are viewed in the context of HIV transmission to susceptible cells and fertilization. The ability of a low-molecular-weight non-peptide integrin modulator to inhibit HIV infection (virus-to-cell and cell-to-cell) and sperm-egg fusion is demonstrated. It is concluded that integrin-modulating substances offer significant promise as female-controlled means for preventing sexual transmission of HIV (whatever entity acts as HIV vector in semen and other penile secretions) and as female-controlled contraceptives.

Do autoantibodies to sperm reduce fecundity? A mini-review in historical perspective

PROBLEM

The paradox that early studies of antisperm antibodies in men showed a strong correlation between titers of circulating antibodies (essentially immunoglobulin [Ig] G) and reduction in conception rates, whereas more recent studies have indicated that the antifertility effect is mainly (or exclusively?) associated with IgA antibodies, impairing sperm migration through cervical mucus, was studied.

METHOD OF STUDY

Relevant literature focusing on antibodies on ejaculated sperm was analyzed.

RESULTS

Direct mixed antiglobulin reaction (MAR) and immunobead-binding tests are excellent and sensitive techniques for demonstrating antibodies of the IgG and IgA classes on sperm, and they have revealed that IgA antibodies are, with very rare exceptions, found only when IgG antibodies are also present. However, these tests tell little about the amounts of antibodies present, and attempts to measure quantitatively the amounts of Ig on sperm have indicated higher levels of IgA than IgG (despite the strongest MAR reactivities for IgG).

CONCLUSIONS

The patients with high levels of IgA to their sperm are mainly men with strong immune responses and, therefore, also high antibody titers in serum. Apparently, the locally produced IgA antibodies reach the sperm and occupy the binding sites before the main bulk of IgG reaches the seminal compartment with the prostatic fluid.