The adhesin complex protein (ACP) of Neisseria meningitidis is a new adhesin with vaccine potential

Characterization of protective immune responses against Neisseria gonorrhoeae induced by intranasal immunization with adhesion and penetration protein

Drug-resistant N. gonorrhoeae is an urgent threat to global public health, and vaccine development is the best long-term strategy for controlling gonorrhea. We have previously shown that adhesion and penetration protein (App) play a role in the adhesion, invasion, and reproductive tract colonization of N. gonorrhoeae. Here, we describe the immune response induced by intranasal immunization with passenger and translocator fragments of App. The recombinant App passenger and translocator fragments induced high titers of IgG and IgA antibodies in serum and vaginal washes. Antibodies produced by App passenger and the combination of passenger and translocator mediated the killing of N. gonorrhoeae via serum bactericidal activity and opsonophagocytic activity, whereas antisera from translocator-immunized groups had lower bactericidal activity and opsonophagocytic activity. The antisera of the App passenger and translocator, alone and in combination, inhibited the adhesion of N. gonorrhoeae to cervical epithelial cells in a concentration-dependent manner. Nasal immunization with App passenger and translocator fragments alone or in combination induced high levels of IgG1, IgG2a, and IgG2b antibodies and stimulated mouse splenocytes to secrete cytokines IFN-γ and IL-17A, suggesting that Th1 and Th17 cellular immune responses were activated. In vivo experiments have shown that immune App passenger and transporter fragments can accelerate the clearance of N. gonorrhoeae in the vagina of mice. These data suggest that the App protein is a promising N. gonorrhoeae vaccine antigen.

A genome-wide transposon mutagenesis screening identifies LppB as a key factor associated with Mycoplasma bovis colonization and invasion into host cells

Mycoplasma spp., the smallest self-replicating and genome-reduced organisms, have raised a great concern in both the medical and veterinary fields due to their pathogenicity. The molecular determinants of these wall-less bacterium efficiently use their limited genes to ensure successful infection of the host remain unclear. In the present study, we used the ruminant pathogen Mycoplasma bovis as a model to identify the key factors for colonization and invasion into host cells. We constructed a nonredundant fluorescent transposon mutant library of M. bovis using a modified transposon plasmid, and identified 34 novel adhesion-related genes based on a high-throughput screening approach. Among them, the ΔLppB mutant exhibited the most apparent decrease in adhesion to embryonic bovine lung (EBL) cells. The surface-localized lipoprotein LppB, which is highly conserved in Mycoplasma species, was then confirmed as a key factor for M. bovis adhesion with great immunogenicity. LppB interacted with various components (fibronectin, vitronectin, collagen IV, and laminin) of host extracellular matrix (ECM) and promoted plasminogen activation through tPA to degrade ECM. The 439-502 amino acid region of LppB is a critical domain, and F465 and Y493 are important residues for the plasminogen activation activity. We further revealed LppB as a key factor facilitating internalization through clathrin- and lipid raft-mediated endocytosis, which helps the Mycoplasma invade the host cells. Our study indicates that LppB plays a key role in Mycoplasma infection and is a potential new therapeutic and vaccine target for Mycoplasma species.

Mechanisms of host manipulation by Neisseria gonorrhoeae

Neisseria gonorrhoeae (also known as gonococcus) has been causing gonorrhoea in humans since ancient Egyptian times. Today, global gonorrhoea infections are rising at an alarming rate, in concert with an increasing number of antimicrobial-resistant strains. The gonococcus has concurrently evolved several intricate mechanisms that promote pathogenesis by evading both host immunity and defeating common therapeutic interventions. Central to these adaptations is the ability of the gonococcus to manipulate various host microenvironments upon infection. For example, the gonococcus can survive within neutrophils through direct regulation of both the oxidative burst response and maturation of the phagosome; a concerning trait given the important role neutrophils have in defending against invading pathogens. Hence, a detailed understanding of how N. gonorrhoeae exploits the human host to establish and maintain infection is crucial for combating this pathogen. This review summarizes the mechanisms behind host manipulation, with a central focus on the exploitation of host epithelial cell signaling to promote colonization and invasion of the epithelial lining, the modulation of the host immune response to evade both innate and adaptive defenses, and the manipulation of host cell death pathways to both assist colonization and combat antimicrobial activities of innate immune cells. Collectively, these pathways act in concert to enable N. gonorrhoeae to colonize and invade a wide array of host tissues, both establishing and disseminating gonococcal infection.

Synergistic activity of antibodies in the multicomponent 4CMenB vaccine

INTRODUCTION

: Vaccines based on multiple antigens often induce an immune response which is higher than that triggered by each single component, with antibodies acting cooperatively and synergistically in tackling the infection.

AREAS COVERED

An interesting example is the antibody response induced by the 4CMenB vaccine, currently licensed for the prevention of Neisseria meningitidis serogroup B (MenB). It contains four antigenic components: Factor H binding protein (fHbp), Neisseria adhesin A (NadA), Neisserial Heparin Binding Antigen (NHBA) and Outer Membrane Vesicles (OMV). Monoclonal and polyclonal antibodies raised by vaccination with 4CMenB show synergistic activity in complement-dependent bacterial killing. This review summarizes published and unpublished data and provides evidence of the added value of multicomponent vaccines.

EXPERT OPINION

: The ability of 4CMenB vaccine to elicit antibodies targeting multiple surface-exposed antigens is corroborated by the recent data on real world evidences. Bactericidal activity is generally mediated by antibodies that bind to antigens highly expressed on the bacterial surface and immunologically related. However, simultaneous binding of antibodies to various surface-exposed antigens can overcome the threshold density of antigen-antibody complexes needed for complement activation. The data discussed in this review highlight the interplay between antibodies targeting major and minor antigens and their effect on functionality.

Clinical trial registration: www.clinicaltrials.gov identifiers of studies with original data mentioned in the article: NCT00937521, NCT00433914, NCT02140762 and NCT02285777.

The potential utility of liposomes for Neisseria vaccines

INTRODUCTION

Species of the genus Neisseria are important global pathogens. Neisseria gonorrhoeae (gonococcus) causes the sexually transmitted disease gonorrhea and Neisseria meningitidis (meningococcus) causes meningitis and sepsis. Liposomes are self-assembled spheres of phospholipid bilayers enclosing a central aqueous space, and they have attracted much interest and use as a delivery vehicle for Neisseria vaccine antigens.

AREAS COVERED

A brief background on Neisseria infections and the success of licensed meningococcal vaccines are provided. The absence of a gonococcal vaccine is highlighted. The use of liposomes for delivering Neisseria antigens and adjuvants, for the purposes of generating specific immune responses, is reviewed. The use of other lipid-based systems for antigen and adjuvant delivery is examined briefly.

EXPERT OPINION

With renewed interest in developing a gonococcal vaccine, liposomes remain an attractive option for delivering antigens. The discipline of nanotechnology provides additional nanoparticle-based options for gonococcal vaccine development. Future work would be needed to tailor the composition of liposomes and other nanoparticles to the specific vaccine antigen(s), in order to generate optimal anti-gonococcal immune responses. The potential use of liposomes and other nanoparticles to deliver anti-gonococcal compounds to treat infections also should be explored further.

Adhesins of Brucella: Their Roles in the Interaction with the Host

A central aspect of Brucella pathogenicity is its ability to invade, survive, and replicate in diverse phagocytic and non-phagocytic cell types, leading to chronic infections and chronic inflammatory phenomena. Adhesion to the target cell is a critical first step in the invasion process. Several Brucella adhesins have been shown to mediate adhesion to cells, extracellular matrix components (ECM), or both. These include the sialic acid-binding proteins SP29 and SP41 (binding to erythrocytes and epithelial cells, respectively), the BigA and BigB proteins that contain an Ig-like domain (binding to cell adhesion molecules in epithelial cells), the monomeric autotransporters BmaA, BmaB, and BmaC (binding to ECM components, epithelial cells, osteoblasts, synoviocytes, and trophoblasts), the trimeric autotransporters BtaE and BtaF (binding to ECM components and epithelial cells) and Bp26 (binding to ECM components). An in vivo role has also been shown for the trimeric autotransporters, as deletion mutants display decreased colonization after oral and/or respiratory infection in mice, and it has also been suggested for BigA and BigB. Several adhesins have shown unipolar localization, suggesting that Brucella would express an adhesive pole. Adhesin-based vaccines may be useful to prevent brucellosis, as intranasal immunization in mice with BtaF conferred high levels of protection against oral challenge with B. suis.

Genetic incorporation of non-canonical amino acid photocrosslinkers in Neisseria meningitidis: New method provides insights into the physiological function of the function-unknown NMB1345 protein

Although whole-genome sequencing has provided novel insights into Neisseria meningitidis, many open reading frames have only been annotated as hypothetical proteins with unknown biological functions. Our previous genetic analyses revealed that the hypothetical protein, NMB1345, plays a crucial role in meningococcal infection in human brain microvascular endothelial cells; however, NMB1345 has no homology to any identified protein in databases and its physiological function could not be elucidated using pre-existing methods. Among the many biological technologies to examine transient protein-protein interaction in vivo, one of the developed methods is genetic code expansion with non-canonical amino acids (ncAAs) utilizing a pyrrolysyl-tRNA synthetase/tRNAPyl pair from Methanosarcina species: However, this method has never been applied to assign function-unknown proteins in pathogenic bacteria. In the present study, we developed a new method to genetically incorporate ncAAs-encoded photocrosslinking probes into N. meningitidis by utilizing a pyrrolysyl-tRNA synthetase/tRNAPyl pair and elucidated the biological function(s) of the NMB1345 protein. The results revealed that the NMB1345 protein directly interacts with PilE, a major component of meningococcal pili, and further physicochemical and genetic analyses showed that the interaction between the NMB1345 protein and PilE was important for both functional pilus formation and meningococcal infectious ability in N. meningitidis. The present study using this new methodology for N. meningitidis provides novel insights into meningococcal pathogenesis by assigning the function of a hypothetical protein.

Bactericidal Effect of 5-Mercapto-2-nitrobenzoic Acid-Coated Silver Nanoclusters against Multidrug-Resistant Neisseria gonorrhoeae

Neisseria gonorrhoeae is among the most multidrug-resistant bacteria in circulation today, and new treatments are urgently needed. In this work, we demonstrate the ability of 5-mercapto-2-nitrobenzoic acid-coated silver nanoclusters (MNBA-AgNCs) to kill strains of Neisseria gonorrhoeae. Using an in vitro bactericidal assay, MNBA-AgNCs had been found to show significantly higher anti-gonococcal bioactivity than the antibiotics ceftriaxone and azithromycin and silver nitrate. These nanoclusters were effective against both planktonic bacteria and a gonococcal infection of human cell cultures in vitro. Treatment of human cells in vitro with MNBA-AgNCs did not induce significant release of lactate dehydrogenase, suggesting minimal cytotoxicity to eukaryotic cells. Our results suggest that MNBA-AgNCs hold great potential for topical treatment of localized gonorrhoeae.

Effect of Lipidation on the Localization and Activity of a Lysozyme Inhibitor in Neisseria gonorrhoeae

The Gram-negative pathogen Neisseria gonorrhoeae (gonococcus [Gc]) colonizes lysozyme-rich mucosal surfaces. Lysozyme hydrolyzes peptidoglycan, leading to bacterial lysis. Gc expresses two proteins, SliC and NgACP, that bind and inhibit the enzymatic activity of lysozyme. SliC is a surface-exposed lipoprotein, while NgACP is found in the periplasm and also released extracellularly. Purified SliC and NgACP similarly inhibit lysozyme. However, whereas mutation of ngACP increases Gc susceptibility to lysozyme, the sliC mutant is only susceptible to lysozyme when ngACP is inactivated. In this work, we examined how lipidation contributes to SliC expression, cellular localization, and resistance of Gc to killing by lysozyme. To do so, we mutated the conserved cysteine residue (C18) in the N-terminal lipobox motif of SliC, the site for lipid anchor attachment, to alanine. SliC(C18A) localized to soluble rather than membrane fractions in Gc and was not displayed on the bacterial surface. Less SliC(C18A) was detected in Gc lysates compared to the wild-type protein. This was due in part to some release of the C18A mutant, but not wild-type, protein into the extracellular space. Surprisingly, Gc expressing SliC(C18A) survived better than SliC (wild type)-expressing Gc after exposure to lysozyme. We conclude that lipidation is not required for the ability of SliC to inhibit lysozyme, even though the lipidated cysteine is 100% conserved in Gc SliC alleles. These findings shed light on how members of the growing family of lysozyme inhibitors with distinct subcellular localizations contribute to bacterial defense against lysozyme.IMPORTANCE Neisseria gonorrhoeae is one of many bacterial species that express multiple lysozyme inhibitors. It is unclear how inhibitors that differ in their subcellular localization contribute to defense from lysozyme. We investigated how lipidation of SliC, an MliC (membrane-bound lysozyme inhibitor of c-type lysozyme)-type inhibitor, contributes to its localization and lysozyme inhibitory activity. We found that lipidation was required for surface exposure of SliC and yet was dispensable for protecting the gonococcus from killing by lysozyme. To our knowledge, this is the first time the role of lipid anchoring of a lysozyme inhibitor has been investigated. These results help us understand how different lysozyme inhibitors are localized in bacteria and how this impacts resistance to lysozyme.

Commensal Neisseria cinerea impairs Neisseria meningitidis microcolony development and reduces pathogen colonisation of epithelial cells

It is increasingly being recognised that the interplay between commensal and pathogenic bacteria can dictate the outcome of infection. Consequently, there is a need to understand how commensals interact with their human host and influence pathogen behaviour at epithelial surfaces. Neisseria meningitidis, a leading cause of sepsis and meningitis, exclusively colonises the human nasopharynx and shares this niche with several other Neisseria species, including the commensal Neisseria cinerea. Here, we demonstrate that during adhesion to human epithelial cells N. cinerea co-localises with molecules that are also recruited by the meningococcus, and show that, similar to N. meningitidis, N. cinerea forms dynamic microcolonies on the cell surface in a Type four pilus (Tfp) dependent manner. Finally, we demonstrate that N. cinerea colocalises with N. meningitidis on the epithelial cell surface, limits the size and motility of meningococcal microcolonies, and impairs the effective colonisation of epithelial cells by the pathogen. Our data establish that commensal Neisseria can mimic and affect the behaviour of a pathogen on epithelial cell surfaces.

Strategies used by bacterial pathogens to cross the blood-brain barrier

The skull, spine, meninges, and cellular barriers at the blood-brain and the blood-cerebrospinal fluid interfaces well protect the brain and meningeal spaces against microbial invasion. However, once in the bloodstream, a range of pathogenic bacteria is able to reach the brain and cause meningitis. Despite advances in antibacterial therapy, bacterial meningitis remains one of the most important infectious diseases worldwide. The most common causative bacteria in children and adults are Streptococcus pneumoniae and Neisseria meningitidis associated with high morbidity and mortality, while among neonates, most cases of bacterial meningitis are due to group B Streptococcus and Escherichia coli. Here we summarise our current knowledge on the strategies used by these bacterial pathogens to survive in the bloodstream, to colonise the brain vasculature and to cross the blood-brain barrier.

Characterization of two putative Dichelobacter nodosus footrot vaccine antigens identifies the first lysozyme inhibitor in the genus

The Gram-negative anaerobic bacterium Dichelobacter nodosus (Dn) causes footrot in ruminants, a debilitating and highly contagious disease that results in necrotic hooves and significant economic losses in agriculture. Vaccination with crude whole-cell vaccine mixed with multiple recombinant fimbrial proteins can provide protection during species-specific outbreaks, but subunit vaccines containing broadly cross-protective antigens are desirable. We have investigated two D. nodosus candidate vaccine antigens. Macrophage Infectivity Potentiator Dn-MIP (DNO_0012, DNO_RS00050) and Adhesin Complex Protein Dn-ACP (DNO_0725, DNO_RS06795) are highly conserved amongst ~170 D. nodosus isolates in the https://pubmlst.org/dnodosus/ database. We describe the presence of two homologous ACP domains in Dn-ACP with potent C-type lysozyme inhibitor function, and homology of Dn-MIP to other putative cell-surface and membrane-anchored MIP virulence factors. Immunization of mice with recombinant proteins with a variety of adjuvants induced antibodies that recognised both proteins in D. nodosus. Notably, immunization with fimbrial-whole-cell Footvax vaccine induced anti-Dn-ACP and anti-Dn-MIP antibodies. Although all adjuvants induced high titre antibody responses, only antisera to rDn-ACP-QuilA and rDn-ACP-Al(OH)₃ significantly prevented rDn-ACP protein from inhibiting lysozyme activity in vitro. Therefore, a vaccine incorporating rDn-ACP in particular could contribute to protection by enabling normal innate immune lysozyme function to aid bacterial clearance.

Neisseria gonorrhoeae MlaA influences gonococcal virulence and membrane vesicle production

The six-component maintenance of lipid asymmetry (Mla) system is responsible for retrograde transport of phospholipids, ensuring the barrier function of the Gram-negative cell envelope. Located within the outer membrane, MlaA (VacJ) acts as a channel to shuttle phospholipids from the outer leaflet. We identified Neisseria gonorrhoeae MlaA (ngo2121) during high-throughput proteomic mining for potential therapeutic targets against this medically important human pathogen. Our follow-up phenotypic microarrays revealed that lack of MlaA results in a complex sensitivity phenome. Herein we focused on MlaA function in cell envelope biogenesis and pathogenesis. We demonstrate the existence of two MlaA classes among 21 bacterial species, characterized by the presence or lack of a lipoprotein signal peptide. Purified truncated N. gonorrhoeae MlaA elicited antibodies that cross-reacted with a panel of different Neisseria. Little is known about MlaA expression; we provide the first evidence that MlaA levels increase in stationary phase and under anaerobiosis but decrease during iron starvation. Lack of MlaA resulted in higher cell counts during conditions mimicking different host niches; however, it also significantly decreased colony size. Antimicrobial peptides such as polymyxin B exacerbated the size difference while human defensin was detrimental to mutant viability. Consistent with the proposed role of MlaA in vesicle biogenesis, the ΔmlaA mutant released 1.7-fold more membrane vesicles. Comparative proteomics of cell envelopes and native membrane vesicles derived from ΔmlaA and wild type bacteria revealed enrichment of TadA–which recodes proteins through mRNA editing–as well as increased levels of adhesins and virulence factors. MlaA-deficient gonococci significantly outcompeted (up to 16-fold) wild-type bacteria in the murine lower genital tract, suggesting the growth advantage or increased expression of virulence factors afforded by inactivation of mlaA is advantageous in vivo. Based on these results, we propose N. gonorrhoeae restricts MlaA levels to modulate cell envelope homeostasis and fine-tune virulence.

The Gram-negative outer membrane is a formidable barrier, primarily because of its asymmetric composition. A layer of lipopolysaccharide is exposed to the external environment and phospholipids are on the internal face of the outer membrane. MlaA is part of a bacterial system that prevents phospholipid accumulation within the lipopolysaccharide layer. If MlaA is removed, membrane asymmetry is disrupted and bacteria become more vulnerable to certain antimicrobials. Neisseria gonorrhoeae causes millions of infections worldwide annually. A growing number are resistant to available antibiotics. Improving our understanding of gonococcal pathogenicity and basic biological processes is required to facilitate the discovery of new weapons against gonorrhea. We investigated the role of MlaA in N. gonorrhoeae and found that when MlaA was absent, bacteria were more sensitive to antibiotics and human defensins. However, the mutant bacteria produced more membrane vesicles–packages of proteins wrapped in membrane material. Mutant vesicles and cell envelopes were enriched in proteins that contribute to disease. These alterations significantly increased mutant fitness during experimental infection of the female mouse genital tract. Our results provide new insights into the processes N. gonorrhoeae uses to fine-tune its ability to stay fit in the hostile environment of the genital tract.

Quantitative Proteomics of the 2016 WHO Neisseria gonorrhoeae Reference Strains Surveys Vaccine Candidates and Antimicrobial Resistance Determinants

The sexually transmitted disease gonorrhea (causative agent: Neisseria gonorrhoeae) remains an urgent public health threat globally because of its reproductive health repercussions, high incidence, widespread antimicrobial resistance (AMR), and absence of a vaccine. To mine gonorrhea antigens and enhance our understanding of gonococcal AMR at the proteome level, we performed the first large-scale proteomic profiling of a diverse panel (n = 15) of gonococcal strains, including the 2016 World Health Organization (WHO) reference strains. These strains show all existing AMR profiles - established through phenotypic characterization and reference genome publication - and are intended for quality assurance in laboratory investigations. Herein, these isolates were subjected to subcellular fractionation and labeling with tandem mass tags coupled to mass spectrometry and multi-combinatorial bioinformatics. Our analyses detected 904 and 723 common proteins in cell envelope and cytoplasmic subproteomes, respectively. We identified nine novel gonorrhea vaccine candidates. Expression and conservation of new and previously selected antigens were investigated. In addition, established gonococcal AMR determinants were evaluated for the first time using quantitative proteomics. Six new proteins, WHO_F_00238, WHO_F_00635c, WHO_F_00745, WHO_F_01139, WHO_F_01144c, and WHO_F_01126, were differentially expressed in all strains, suggesting that they represent global proteomic AMR markers, indicate a predisposition toward developing or compensating gonococcal AMR, and/or act as new antimicrobial targets. Finally, phenotypic clustering based on the isolates' defined antibiograms and common differentially expressed proteins yielded seven matching clusters between established and proteome-derived AMR signatures. Together, our investigations provide a reference proteomics data bank for gonococcal vaccine and AMR research endeavors, which enables microbiological, clinical, or epidemiological projects and enhances the utility of the WHO reference strains.

The Meningococcal Cysteine Transport System Plays a Crucial Role in Neisseria meningitidis Survival in Human Brain Microvascular Endothelial Cells

Neisseria meningitidis colonizes at a nasopharynx of human as a unique host and has many strains that are auxotrophs for amino acids for their growth. To cause invasive meningococcal diseases (IMD) such as sepsis and meningitis, N. meningitidis passes through epithelial and endothelial barriers and infiltrates into blood and cerebrospinal fluid as well as epithelial and endothelial cells. However, meningococcal nutrients, including cysteine, become less abundant when it more deeply infiltrates the human body even during inflammation, such that N. meningitidis has to acquire nutrients in order to survive/persist, disseminate, and proliferate in humans. This was the first study to examine the relationship between meningococcal cysteine acquisition and the pathogenesis of meningococcal infections. The results of the present study provide insights into the mechanisms by which pathogens with auxotrophs acquire nutrients in hosts and may also contribute to the development of treatments and prevention strategies for IMD.

While Neisseria meningitidis typically exists in an asymptomatic nasopharyngeal carriage state, it may cause potentially lethal diseases in humans, such as septicemia or meningitis, by invading deeper sites in the body. Since the nutrient compositions of human cells are not always conducive to meningococci, N. meningitidis needs to exploit nutrients from host environments. In the present study, the utilization of cysteine by the meningococcal cysteine transport system (CTS) was analyzed for the pathogenesis of meningococcal infections. A N. meningitidis strain deficient in one of the three cts genes annotated as encoding cysteine-binding protein (cbp) exhibited approximately 100-fold less internalization into human brain microvascular endothelial cells (HBMEC) than the wild-type strain. This deficiency was restored by complementation with the three cts genes together, and the infectious phenotype of HBMEC internalization correlated with cysteine uptake activity. However, efficient accumulation of ezrin was observed beneath the cbp mutant. The intracellular survival of the cbp mutant in HBMEC was markedly reduced, whereas equivalent reductions of glutathione concentrations and of resistance to reactive oxygens species in the cbp mutant were not found. The cbp mutant grew well in complete medium but not in synthetic medium supplemented with less than 300 μM cysteine. Taking cysteine concentrations in human cells and other body fluids, including blood and cerebrospinal fluid, into consideration, the present results collectively suggest that the meningococcal CTS is crucial for the acquisition of cysteine from human cells and participates in meningococcal nutrient virulence.

Proteomics, Bioinformatics and Structure-Function Antigen Mining For Gonorrhea Vaccines

Expanding efforts to develop preventive gonorrhea vaccines is critical because of the serious health consequences combined with the prevalence and the dire possibility of untreatable gonorrhea. Reverse vaccinology, which includes genome and proteome mining, has proven successful in the discovery of vaccine candidates against many pathogenic bacteria. Here, we describe proteomic applications including comprehensive, quantitative proteomic platforms and immunoproteomics coupled with broad-ranging bioinformatics that have been applied for antigen mining to develop gonorrhea vaccine(s). We further focus on outlining the vaccine candidate decision tree, describe the structure-function of novel proteome-derived antigens as well as ways to gain insights into their roles in the cell envelope, and underscore new lessons learned about the fascinating biology of Neisseria gonorrhoeae.

Structure of the Recombinant Neisseria gonorrhoeae Adhesin Complex Protein (rNg-ACP) and Generation of Murine Antibodies with Bactericidal Activity against Gonococci

Neisseria gonorrhoeae (gonococcus [Ng]) is the causative organism of the sexually transmitted disease gonorrhoea, and the organism is listed by the World Health Organization as a high-priority pathogen for research and development of new control measures, including vaccines. In this study, we demonstrated that the N. gonorrhoeae adhesin complex protein (Ng-ACP) was conserved and expressed by 50 gonococcal strains and that recombinant proteins induced antibodies in mice that killed the bacteria in vitro. We determined the structure of Ng-ACP by X-ray crystallography and investigated structural conservation with Neisseria meningitidis ACP and MliC/PliC proteins from other bacteria which act as inhibitors of the human innate defense molecule lysozyme. These findings are important and suggest that Ng-ACP could provide a potential dual target for tackling gonococcal infections.

Neisseria gonorrhoeae (gonococcus [Ng]) is the causative organism of the sexually transmitted disease gonorrhoea, and no effective vaccine exists currently. In this study, the structure, biological properties, and vaccine potential of the Ng-adhesin complex protein (Ng-ACP) are presented. The crystal structure of recombinant Ng-ACP (rNg-ACP) protein was solved at 1.65 Å. Diversity and conservation of Ng-ACP were examined in different Neisseria species and gonococcal isolates (https://pubmlst.org/neisseria/ database) in silico, and protein expression among 50 gonococcal strains in the Centers for Disease Control and Prevention/Food and Drug Administration (CDCP/FDA) AR Isolate Bank was examined by Western blotting. Murine antisera were raised to allele 10 (strain P9-17)-encoded rNg-ACP protein with different adjuvants and examined by enzyme-linked immunosorbent assay (ELISA), Western blotting, and a human serum bactericidal assay. Rabbit antiserum to rNg-ACP was tested for its ability to prevent Ng-ACP from inhibiting human lysozyme activity in vitro. Ng-ACP is structurally homologous to Neisseria meningitidis ACP and MliC/PliC lysozyme inhibitors. Gonococci expressed predominantly allele 10- and allele 6-encoded Ng-ACP (81% and 15% of isolates, respectively). Murine antisera were bactericidal (titers of 64 to 512, P < 0.05) for the homologous P9-17 strain and heterologous (allele 6) FA1090 strain. Rabbit anti-rNg-ACP serum prevented Ng-ACP from inhibiting human lysozyme with ∼100% efficiency. Ng-ACP protein was expressed by all 50 gonococcal isolates examined with minor differences in the relative levels of expression. rNg-ACP is a potential vaccine candidate that induces antibodies that (i) are bactericidal and (ii) prevent the gonococcus from inhibiting the lytic activity of an innate defense molecule.

IMPORTANCENeisseria gonorrhoeae (gonococcus [Ng]) is the causative organism of the sexually transmitted disease gonorrhoea, and the organism is listed by the World Health Organization as a high-priority pathogen for research and development of new control measures, including vaccines. In this study, we demonstrated that the N. gonorrhoeae adhesin complex protein (Ng-ACP) was conserved and expressed by 50 gonococcal strains and that recombinant proteins induced antibodies in mice that killed the bacteria in vitro. We determined the structure of Ng-ACP by X-ray crystallography and investigated structural conservation with Neisseria meningitidis ACP and MliC/PliC proteins from other bacteria which act as inhibitors of the human innate defense molecule lysozyme. These findings are important and suggest that Ng-ACP could provide a potential dual target for tackling gonococcal infections.

Neisseria gonorrhoeae employs two protein inhibitors to evade killing by human lysozyme

The bacterial pathogen Neisseria gonorrhoeae (Gc) infects mucosal sites rich in antimicrobial proteins, including the bacterial cell wall-degrading enzyme lysozyme. Certain Gram-negative bacteria produce protein inhibitors that bind to and inhibit lysozyme. Here, we identify Ng_1063 as a new inhibitor of lysozyme in Gc, and we define its functions in light of a second, recently identified lysozyme inhibitor, Ng_1981. In silico analyses indicated that Ng_1063 bears sequence and structural homology to MliC-type inhibitors of lysozyme. Recombinant Ng_1063 inhibited lysozyme-mediated killing of a susceptible mutant of Gc and the lysozyme-sensitive bacterium Micrococcus luteus. This inhibitory activity was dependent on serine 83 and lysine 103 of Ng_1063, which are predicted to interact with lysozyme’s active site residues. Lysozyme co-immunoprecipitated with Ng_1063 and Ng_1981 from intact Gc. Ng_1063 and Ng_1981 protein levels were also increased in Gc exposed to lysozyme. Gc lacking both ng1063 and ng1981 was significantly more sensitive to killing by lysozyme than wild-type or single mutant bacteria. When exposed to human tears or saliva, in which lysozyme is abundant, survival of Δ1981Δ1063 Gc was significantly reduced compared to wild-type, and survival was restored upon addition of recombinant Ng_1981. Δ1981Δ1063 mutant Gc survival was additionally reduced in the presence of human neutrophils, which produce lysozyme. We found that while Ng_1063 was exposed on the surface of Gc, Ng_1981 was both in an intracellular pool and extracellularly released from the bacteria, suggesting that Gc employs these two proteins at multiple spatial barriers to fully neutralize lysozyme activity. Together, these findings identify Ng_1063 and Ng_1981 as critical components for Gc defense against lysozyme. These proteins may be attractive targets for antimicrobial therapy aimed to render Gc susceptible to host defenses and/or for vaccine development, both of which are urgently needed against drug-resistant gonorrhea.

The mucosal pathogen Neisseria gonorrhoeae has acquired resistance to almost all recommended antibiotics, and no gonorrhea vaccine currently exists. Attractive targets for therapeutic discovery include bacterial factors that, when inactivated, enhance bacterial susceptibility to host-derived antimicrobial components. The bacterial cell wall-degrading enzyme lysozyme is abundant in mucosal secretions and innate immune cells. To resist killing by lysozyme, some bacteria produce proteins that bind to and directly inhibit the activity of lysozyme. Here, we demonstrate lysozyme inhibitory activity in the N. gonorrhoeae protein Ng_1063. We found that both Ng_1063 and a second, recently described lysozyme inhibitor, Ng_1981, contribute to full resistance of N. gonorrhoeae to lysozyme, including resistance to lysozyme-rich mucosal secretions and human neutrophils. Although Ng_1063 and Ng_1981 are both inhibitors of lysozyme, they are distinct in their sequences, biological activities, and cellular localizations. Because both Ng_1063 and Ng_1981 are extracellular, we propose they can be targeted for vaccines and drugs that sensitize Gc to human antimicrobial defenses.

SliC is a surface-displayed lipoprotein that is required for the anti-lysozyme strategy during Neisseria gonorrhoeae infection

Lysozymes are nearly omnipresent as the first line of immune defense against microbes in animals. They exert bactericidal action through antimicrobial peptide activity and peptidoglycan hydrolysis. Gram-negative bacteria developed several weapons to battle lysozymes, including inhibitors of c-type lysozymes in the MliC/PliC family and the Neisseria adhesin complex protein (ACP). Until the recent discovery of ACP, no proteinaceous lysozyme inhibitors were reported for the genus Neisseria, including the important human pathogen N. gonorrhoeae. Here, we describe a previously unrecognized gonococcal virulence mechanism involving a protein encoded by the open reading frame ngo1063 that acts to counteract c-type Iysozyme and provides a competitive advantage in the murine model of gonorrhea. We named this protein SliC as a surface-exposed lysozyme inhibitor of c-type lysozyme. SliC displays low overall primary sequence similarity to the MliC/PliC inhibitors, but we demonstrate that it has a parallel inhibitory mechanism. Our studies provide the first evidence that bacterial proteinaceous lysozyme inhibitors protect against host lysozyme during infection based on lack of attenuation of the ΔsliC mutant in lysozyme knock-out mice, and that the conserved residues involved in lysozyme inhibition, S83 and K103, are functionally indispensable during infection in wild type mice. Recombinant SliC completely abrogated the lytic activity of human and chicken c-type lysozymes, showing a preference towards human lysozyme with an IC₅₀ of 1.85 μM and calculated K_D value of 9.2 ± 1.9 μM. In contrast, mutated SliC bearing S83A and K103A substitutions failed to protect fluorescein-labeled cell-wall from lysozyme-mediated hydrolysis. Further, we present data revealing that SliC is a surface-displayed lipoprotein released in membrane vesicles that is expressed throughout all phases of growth, in conditions relevant to different niches of the human host, and during experimental infection of the murine genital tract. SliC is also highly conserved and expressed by diverse gonococcal isolates as well as N. meningitidis, N. lactamica, and N. weaveri. This study is the first to highlight the importance of an anti-lysozyme strategy to escape the innate immune response during N. gonorrhoeae infection.

Neisseria gonorrhoeae, the etiologic agent of gonorrhea, is a clinically important pathogen due to the emergence of multi-drug resistance and the lack of a vaccine(s). During host colonization, pathogenic and commensal Neisseria inevitably encounter lysozyme, a major host innate defense factor that is abundantly present in epithelial secretions and phagocytic cells. Although Neisseria spp produce a c-type lysozyme inhibitor, the Adhesin Complex Protein, the significance of lysozyme inhibition for host colonization has not been addressed. Here we demonstrate the existence of a new c-type lysozyme inhibitor in Neisseria. We show that it is a surface-displayed lipoprotein in N. gonorrhoeae and, through its lysozyme-blocking function, plays a critical role in colonization of genital tract mucosae during infection in the female gonorrhea mouse model. We named the protein SliC as a surface-exposed lysozyme inhibitor of c-type lysozyme. Understanding the mechanisms underlying anti-lysozyme strategies may facilitate antimicrobial development.

The meninges as barriers and facilitators for the movement of fluid, cells and pathogens related to the rodent and human CNS

Meninges that surround the CNS consist of an outer fibrous sheet of dura mater (pachymeninx) that is also the inner periosteum of the skull. Underlying the dura are the arachnoid and pia mater (leptomeninges) that form the boundaries of the subarachnoid space. In this review we (1) examine the development of leptomeninges and their role as barriers and facilitators in the foetal CNS. There are two separate CSF systems during early foetal life, inner CSF in the ventricles and outer CSF in the subarachnoid space. As the foramina of Magendi and Luschka develop, one continuous CSF system evolves. Due to the lack of arachnoid granulations during foetal life, it is most likely that CSF is eliminated by lymphatic drainage pathways passing through the cribriform plate and nasal submucosa. (2) We then review the fine structure of the adult human and rodent leptomeninges to establish their roles as barriers and facilitators for the movement of fluid, cells and pathogens. Leptomeningeal cells line CSF spaces, including arachnoid granulations and lymphatic drainage pathways, and separate elements of extracellular matrix from the CSF. The leptomeningeal lining facilitates the traffic of inflammatory cells within CSF but also allows attachment of bacteria such as Neisseria meningitidis and of tumour cells as CSF metastases. Single layers of leptomeningeal cells extend into the brain closely associated with the walls of arteries so that there are no perivascular spaces around arteries in the cerebral cortex. Perivascular spaces surrounding arteries in the white matter and basal ganglia relate to their two encompassing layers of leptomeninges. (3) Finally we examine the roles of ligands expressed by leptomeningeal cells for the attachment of inflammatory cells, bacteria and tumour cells as understanding these roles may aid the design of therapeutic strategies to manage developmental, autoimmune, infectious and neoplastic diseases relating to the CSF, the leptomeninges and the associated CNS.

Meningococcal Vaccines: Current Status and Emerging Strategies

Neisseria meningitidis causes most cases of bacterial meningitis. Meningococcal meningitis is a public health burden to both developed and developing countries throughout the world. There are a number of vaccines (polysaccharide-based, glycoconjugate, protein-based and combined conjugate vaccines) that are approved to target five of the six disease-causing serogroups of the pathogen. Immunization strategies have been effective at helping to decrease the global incidence of meningococcal meningitis. Researchers continue to enhance these efforts through discovery of new antigen targets that may lead to a broadly protective vaccine and development of new methods of homogenous vaccine production. This review describes current meningococcal vaccines and discusses some recent research discoveries that may transform vaccine development against N. meningitidis in the future.

Effect of Different Antibiotic Chemotherapies on Pseudomonas aeruginosa Infection In Vitro of Primary Human Corneal Fibroblast Cells

Pseudomonas aeruginosa is a major cause of bacterial keratitis (BK) worldwide. Inappropriate or non-optimal antibiotic chemotherapy can lead to corneal perforation and rapid sight loss. In this study, we tested the hypothesis that P. aeruginosa strain PAO1 invades primary human corneal fibroblasts (hCFs) in vitro and persists intracellularly, despite chemotherapy with antibiotics used commonly to treat BK. In rank order, ciprofloxacin, levofloxacin and polymyxin B showed the highest activity against planktonic PAO1 growth (100% inhibitory concentration ≤10 μg/mL; 50% inhibitory concentration ≤1 μg/mL), followed by gentamicin and ofloxacin (100% inhibitory concentration ≤50 μg/mL; 50% inhibitory concentration ≤10 μg/mL). These bactericidal antibiotics (50–200 μg/mL concentrations) all killed PAO1 in the extracellular environment of infected hCF monolayers. By contrast, the bactericidal antibiotic cefuroxime and the bacteriostatic antibiotic chloramphenicol failed to sterilize both PAO1 broth cultures, even at a concentration of ≥200 μg/mL) and infected hCF monolayers. Statistically, all antibiotics were able to prevent LDH release from PAO1-infected hCF monolayers at both concentrations tested. Intracellular Pseudomonas were significantly reduced (>99%, P < 0.05) following treatment with ciprofloxacin, levofloxacin and ofloxacin, whereas gentamicin, polymyxin B and cefuroxime failed to clear intracellular bacteria over 24 h. Intracellular Pseudomonas infection was resistant to chloramphenicol, with hCF death observed by 9 h. Eventual growth of remaining intracellular Pseudomonas was observed in hCF after removal of all antibiotics, resulting in re-infection cycles and cell death by 48 h. All of the antibiotics reduced significantly (P < 0.05) IL-1β secretion by hCF infected with a Multiplicity Of Infection (MOI) = 1 of PAO1. With higher MOI, no pro-inflammatory effects were observed with antibiotic treatment, expect with polymyxin B and ofloxacin, which induced significant increased IL-1β secretion (P < 0.001). The findings from our study demonstrated that bactericidal and bacteriostatic antibiotics, routinely used to treat BK, failed to eradicate Pseudomonas infection of hCFs in vitro and that their bactericidal efficacies were influenced by the cellular location of the organism.

Structure of the Neisseria Adhesin Complex Protein (ACP) and its role as a novel lysozyme inhibitor

Pathogenic and commensal Neisseria species produce an Adhesin Complex Protein, which was first characterised in Neisseria meningitidis (Nm) as a novel surface-exposed adhesin with vaccine potential. In the current study, the crystal structure of a recombinant (r)Nm-ACP Type I protein was determined to 1.4 Å resolution: the fold resembles an eight-stranded β-barrel, stabilized by a disulphide bond between the first (Cys38) and last (Cys121) β-strands. There are few main-chain hydrogen bonds linking β4-β5 and β8-β1, so the structure divides into two four-stranded anti-parallel β-sheets (β1-β4 and β5-β8). The computed surface electrostatic charge distribution showed that the β1-β4 sheet face is predominantly basic, whereas the β5-β8 sheet is apolar, apart from the loop between β4 and β5. Concentrations of rNm-ACP and rNeisseria gonorrhoeae-ACP proteins ≥0.25 μg/ml significantly inhibited by ~80–100% (P<0.05) the in vitro activity of human lysozyme (HL) over 24 h. Specificity was demonstrated by the ability of murine anti-Neisseria ACP sera to block ACP inhibition and restore HL activity. ACP expression conferred tolerance to HL activity, as demonstrated by significant 3–9 fold reductions (P<0.05) in the growth of meningococcal and gonococcal acp gene knock-out mutants in the presence of lysozyme. In addition, wild-type Neisseria lactamica treated with purified ACP-specific rabbit IgG antibodies showed similar fold reductions in bacterial growth, compared with untreated bacteria (P<0.05). Nm-ACPI is structurally similar to the MliC/PliC protein family of lysozyme inhibitors. However, Neisseria ACP proteins show <20% primary sequence similarity with these inhibitors and do not share any conserved MliC/PliC sequence motifs associated with lysozyme recognition. These observations suggest that Neisseria ACP adopts a different mode of lysozyme inhibition and that the ability of ACP to inhibit lysozyme activity could be important for host colonization by both pathogenic and commensal Neisseria organisms. Thus, ACP represents a dual target for developing Neisseria vaccines and drugs to inhibit host-pathogen interactions.

The genus Neisseria contains two major human pathogens: N. meningitidis (Nm) causes meningitis and sepsis, and N. gonorrhoeae (Ng) causes the sexually transmitted disease gonorrhoea. In addition, the genus contains a larger number of commensal organisms, including N. lactamica (Nl). Common to all of these organisms is the ability to colonize exposed mucosal epithelia. Recently, we identified a novel surface-exposed adhesin in Neisseria spp., the Adhesin Complex Protein (ACP), which was capable also of generating a functional bactericidal antibody response in mice. In the current study, we have determined the crystal structure of a recombinant (r)Nm-ACP and shown that it shares structural homology to bacterial lysozyme inhibitors. We demonstrate that Neisseria ACP functions as an inhibitor of mammalian lysozyme but the mechanism appears to be different from other bacterial family lysozyme inhibitors. Expression of ACP enables Neisseria spp. to tolerate human lysozyme. We propose that ACP-mediated inhibition of lysozyme activity could be important for host colonization by both pathogenic and commensal Neisseria organisms and that ACP represents not only a target for developing Neisseria vaccines but also drugs to inhibit host-pathogen interactions.

Impact of Moderate Temperature Changes on Neisseria meningitidis Adhesion Phenotypes and Proteome

Neisseria meningitidis, the meningococcus, bears the potential to cause life-threatening invasive diseases, but it usually colonizes the nasopharynx without causing any symptoms. Within the nasopharynx, Neisseria meningitidis must face temperature changes depending on the ambient air temperature. Indeed, the nasopharyngeal temperature can be substantially lower than 37°C, the temperature commonly used in experimental settings. Here, we compared the levels of meningococcal biofilm formation, autoaggregation, and cellular adherence at 32°C and 37°C and found a clear increase in all these phenotypes at 32°C suggestive of a stronger in vivo colonization capability at this temperature. A comparative proteome analysis approach revealed differential protein expression levels between 32°C and 37°C, predominantly affecting the bacterial envelope. A total of 375 proteins were detected. Use of database annotation or the PSORTb algorithm predicted 49 of those proteins to be localized in the outer membrane, 21 in either the inner or outer membrane, 35 in the periplasm, 56 in the inner membrane, and 208 in the cytosol; for 6 proteins, no annotation or prediction was available. Temperature-dependent regulation of protein expression was seen particularly in the periplasm as well as in the outer and inner membranes. Neisserial heparin binding antigen (NHBA), NMB1030, and adhesin complex protein (ACP) showed the strongest upregulation at 32°C and were partially responsible for the observed temperature-dependent phenotypes. Screening of different global regulators of Neisseria meningitidis suggested that the extracytoplasmic sigma factor σ^E might be involved in temperature-dependent biofilm formation. In conclusion, subtle temperature changes trigger adaptation events promoting mucosal colonization by meningococci.

Neisserial Heparin Binding Antigen (NHBA) Contributes to the Adhesion of Neisseria meningitidis to Human Epithelial Cells

Neisserial Heparin Binding Antigen (NHBA) is a surface-exposed lipoprotein ubiquitously expressed by Neisseria meningitidis strains and an antigen of the Bexsero^® vaccine. NHBA binds heparin through a conserved Arg-rich region that is the target of two proteases, the meningococcal NalP and human lactoferrin (hLf). In this work, in vitro studies showed that recombinant NHBA protein was able to bind epithelial cells and mutations of the Arg-rich tract abrogated this binding. All N-terminal and C-terminal fragments generated by NalP or hLf cleavage, regardless of the presence or absence of the Arg-rich region, did not bind to cells, indicating that a correct positioning of the Arg-rich region within the full length protein is crucial. Moreover, binding was abolished when cells were treated with heparinase III, suggesting that this interaction is mediated by heparan sulfate proteoglycans (HSPGs). N. meningitidis nhba knockout strains showed a significant reduction in adhesion to epithelial cells with respect to isogenic wild-type strains and adhesion of the wild-type strain was inhibited by anti-NHBA antibodies in a dose-dependent manner. Overall, the results demonstrate that NHBA contributes to meningococcal adhesion to epithelial cells through binding to HSPGs and suggest a possible role of anti-Bexsero^® antibodies in the prevention of colonization.

Interactions of meningococcal virulence factors with endothelial cells at the human blood-cerebrospinal fluid barrier and their role in pathogenicity

The Gram-negative extracellular bacterium Neisseria meningitidis is one of the most common aetiological agents of bacterial meningitis affecting predominantly young children worldwide. This bacterium is normally a quiescent coloniser of the upper respiratory tract, but in some individuals it enters the blood stream and causes invasive diseases, such as septicaemia and meningitis. Interactions of N. meningitidis with human endothelial cells are crucially involved in pathogencitiy, and great efforts have been made to understand these molecular interactions. The aim of this review article is to provide an overview of the interactions of meningococcal virulence factors with host endothelial cells at the blood-cerebrospinal fluid barrier.

Vaccine Potential and Diversity of the Putative Cell Binding Factor (CBF, NMB0345/NEIS1825) Protein of Neisseria meningitidis

The cbf gene from Neisseria meningitidis strain MC58 encoding the putative Cell Binding Factor (CBF, NMB0345/NEIS1825) protein was cloned into the pRSETA system and a ~36-kDa recombinant (r)CBF protein expressed in Escherichia coli and purified by metal affinity chromatography. High titres of rCBF antibodies were induced in mice following immunization with rCBF-saline, rCBF-Al(OH)3, rCBF-Liposomes or rCBF-Zwittergent (Zw) 3-14 micelles, both with and without incorporated monophosphoryl lipid A (MPLA) adjuvant. Anti-rCBF sera reacted in western blots of meningococcal lysates with a single protein band of molecular mass ~29.5 kDa, indicative of mature CBF protein, but did not react with a lysate of a Δnmb0345 mutant (CBF-), demonstrating specificity of the murine immune responses. CBF protein was produced by all strains of meningococci studied thus far and the protein was present on the surface of MC58 (CBF+) bacteria, but absent on Δnmb0345 mutant (CBF-) bacteria, as judged by FACS reactivity of anti-rCBF sera. Analysis of the NEIS1825 amino acid sequences from 6644 N. meningitidis isolates with defined Alleles in the pubmlst.org/Neisseria database showed that there were 141 ST types represented and there were 136 different allelic loci encoding 49 non-redundant protein sequences. Only 6/6644 (<0.1%) of N. meningitidis isolates lacked the nmb0345 gene. Amongst serogroup B isolates worldwide, ~68% and ~20% expressed CBF encoded by Allele 1 and 18 respectively, with the proteins sharing >99% amino acid identity. Murine antisera to rCBF in Zw 3-14 micelles + MPLA induced significant serum bactericidal activity (SBA) against homologous Allele 1 and heterologous Allele 18 strains, using both baby rabbit serum complement and human serum complement (h)SBA assays, but did not kill strains expressing heterologous protein encoded by Alelle 2 or 3. Furthermore, variable bactericidal activity was induced by murine antisera against different meningococcal strains in the hSBA assay, which may correlate with variable surface exposure of CBF. Regardless, the attributes of amino acid sequence conservation and protein expression amongst different strains and the ability to induce cross-strain bactericidal antibodies indicates that rCBF could be a potential meningococcal vaccine antigen and merits further testing.

Neisseria cinerea isolates can adhere to human epithelial cells by type IV pilus-independent mechanisms

In pathogenic Neisseria species the type IV pili (Tfp) are of primary importance in host-pathogen interactions. Tfp mediate initial bacterial attachment to cell surfaces and formation of microcolonies via pilus-pilus interactions. Based on genome analysis, many non-pathogenic Neisseria species are predicted to express Tfp, but aside from studies on Neisseria elongata, relatively little is known about the formation and function of pili in these organisms. Here, we have analysed pilin expression and the role of Tfp in Neisseria cinerea. This non-pathogenic species shares a close taxonomic relationship to the pathogen Neisseria meningitidis and also colonizes the human oropharyngeal cavity. Through analysis of non-pathogenic Neisseria genomes we identified two genes with homology to pilE, which encodes the major pilin of N. meningitidis. We show which of the two genes is required for Tfp expression in N. cinerea and that Tfp in this species are required for DNA competence, similar to other Neisseria. However, in contrast to the meningococcus, deletion of the pilin gene did not impact the association of N. cinerea to human epithelial cells, demonstrating that N. cinerea isolates can adhere to human epithelial cells by Tfp-independent mechanisms.

In silico analysis and modeling of ACP-MIP-PilQ chimeric antigen from Neisseria meningitidis serogroup B

BACKGROUND

Neisseria meningitidis, a life-threatening human pathogen with the potential to cause large epidemics, can be isolated from the nasopharynx of 5-15% of adults. The aim of the current study was to evaluate biophysical and biochemical properties and immunological aspects of chimeric acyl-carrier protein-macrophage infectivity potentiator protein-type IV pilus biogenesis protein antigen (ACP-MIP-PilQ) from N. meningitidis serogroup B strain.

METHODS

Biochemical properties and multiple alignments were predicted by appropriate web servers. Secondary molecular structures were predicted based on Chou and Fasman, Garnier-Osguthorpe-Robson, and Neural Network methods. Tertiary modeling elucidated conformational properties of the chimeric protein. Proteasome cleavage and transporter associated with antigen processing (TAP) binding sites, and T- and B-cell antigenic epitopes, were predicted using bioinformatic web servers.

RESULTS

Based on our in silico and immunoinformatics analyses, the ACP-MIP-PilQ protein (AMP) can induce high-level cross-strain bactericidal activity. In addition, several immune proteasomal cleavage sites were detected. The 22 epitopes associated with MHC class I and class II (DR) alleles were confirmed in the AMP. Thirty linear B-cell epitopes as antigenic regions were predicted from the full-length protein.

CONCLUSION

All predicted properties of the AMP indicate it could be a good candidate for further immunological in vitro and in vivo studies.

How the Knowledge of Interactions between Meningococcus and the Human Immune System Has Been Used to Prepare Effective Neisseria meningitidis Vaccines

In the last decades, tremendous advancement in dissecting the mechanisms of pathogenicity of Neisseria meningitidis at a molecular level has been achieved, exploiting converging approaches of different disciplines, ranging from pathology to microbiology, immunology, and omics sciences (such as genomics and proteomics). Here, we review the molecular biology of the infectious agent and, in particular, its interactions with the immune system, focusing on both the innate and the adaptive responses. Meningococci exploit different mechanisms and complex machineries in order to subvert the immune system and to avoid being killed. Capsular polysaccharide and lipooligosaccharide glycan composition, in particular, play a major role in circumventing immune response. The understanding of these mechanisms has opened new horizons in the field of vaccinology. Nowadays different licensed meningococcal vaccines are available and used: conjugate meningococcal C vaccines, tetravalent conjugate vaccines, an affordable conjugate vaccine against the N. menigitidis serogroup A, and universal vaccines based on multiple antigens each one with a different and peculiar function against meningococcal group B strains.

A putative amino acid ABC transporter substrate-binding protein, NMB1612, from Neisseria meningitidis, induces murine bactericidal antibodies against meningococci expressing heterologous NMB1612 proteins

The nmb1612 (NEIS1533) gene encoding the ~27-kDa putative amino acid ATP-binding cassette (ABC) transporter, periplasmic substrate-binding protein from Neisseria meningitidis serogroup B (MenB) strain MC58 was cloned and expressed in Escherichia coli, and the purified recombinant (r)NMB1612 was used for animal immunization studies. Immunization of mice with rNMB1612 adsorbed to Al(OH)3 and in liposomes with and without MPLA, induced antiserum with bactericidal activity in an assay using baby rabbit complement, against the homologous strain MC58 (encoding protein representative of Allele 62) and killed heterologous strains encoding proteins of three other alleles (representative of Alleles 1, 64 and 68), with similar SBA titres. However, strain MC58 was not killed (titre <4) in a human serum bactericidal assay (hSBA) using anti-rNMB1612 sera, although another strain (MC168) expressing the same protein was killed (median titres of 16-64 in the hSBA). Analysis of the NMB1612 amino acid sequences from 4351 meningococcal strains in the pubmlst.org/Neisseria database and a collection of 13 isolates from colonized individuals and from patients, showed that antibodies raised against rNMB1612 could potentially kill at least 72% of the MenB strains in the complete sequence database. For MenB disease occurring specifically in the UK from 2013 to 2015, >91% of the isolates causing disease in this recent period expressed NMB1612 protein encoded by Allele 1 and could be potentially killed by sera raised to the recombinant antigen in the current study. The NMB1612 protein was surface-accessible and expressed by different meningococcal strains. In summary, the properties of (i) NMB1612 protein conservation and expression, (ii) limited amino acid sequence variation between proteins encoded by different alleles, and (iii) the ability of a recombinant protein to induce cross-strain bactericidal antibodies, would all suggest a promising antigen for consideration for inclusion in new meningococcal vaccines.

Recombinant protein truncation strategy for inducing bactericidal antibodies to the macrophage infectivity potentiator protein of Neisseria meningitidis and circumventing potential cross-reactivity with human FK506-binding proteins

A recombinant macrophage infectivity potentiator (rMIP) protein of Neisseria meningitidis induces significant serum bactericidal antibody production in mice and is a candidate meningococcal vaccine antigen. However, bioinformatics analysis of MIP showed some amino acid sequence similarity to human FK506-binding proteins (FKBPs) in residues 166 to 252 located in the globular domain of the protein. To circumvent the potential concern over generating antibodies that could recognize human proteins, we immunized mice with recombinant truncated type I rMIP proteins that lacked the globular domain and the signal leader peptide (LP) signal sequence (amino acids 1 to 22) and contained the His purification tag at either the N or C terminus (C-term). The immunogenicity of truncated rMIP proteins was compared to that of full (i.e., full-length) rMIP proteins (containing the globular domain) with either an N- or C-terminal His tag and with or without the LP sequence. By comparing the functional murine antibody responses to these various constructs, we determined that C-term His truncated rMIP (-LP) delivered in liposomes induced high levels of antibodies that bound to the surface of wild-type but not Δmip mutant meningococci and showed bactericidal activity against homologous type I MIP (median titers of 128 to 256) and heterologous type II and III (median titers of 256 to 512) strains, thereby providing at least 82% serogroup B strain coverage. In contrast, in constructs lacking the LP, placement of the His tag at the N terminus appeared to abrogate bactericidal activity. The strategy used in this study would obviate any potential concerns regarding the use of MIP antigens for inclusion in bacterial vaccines.

A Moraxella catarrhalis two-component signal transduction system necessary for growth in liquid media affects production of two lysozyme inhibitors

There are a paucity of data concerning gene products that could contribute to the ability of Moraxella catarrhalis to colonize the human nasopharynx. Inactivation of a gene (mesR) encoding a predicted response regulator of a two-component signal transduction system in M. catarrhalis yielded a mutant unable to grow in liquid media. This mesR mutant also exhibited increased sensitivity to certain stressors, including polymyxin B, SDS, and hydrogen peroxide. Inactivation of the gene (mesS) encoding the predicted cognate sensor (histidine) kinase yielded a mutant with the same inability to grow in liquid media as the mesR mutant. DNA microarray and real-time reverse transcriptase PCR analyses indicated that several genes previously shown to be involved in the ability of M. catarrhalis to persist in the chinchilla nasopharynx were upregulated in the mesR mutant. Two other open reading frames upregulated in the mesR mutant were shown to encode small proteins (LipA and LipB) that had amino acid sequence homology to bacterial adhesins and structural homology to bacterial lysozyme inhibitors. Inactivation of both lipA and lipB did not affect the ability of M. catarrhalis O35E to attach to a human bronchial epithelial cell line in vitro. Purified recombinant LipA and LipB fusion proteins were each shown to inhibit human lysozyme activity in vitro and in saliva. A lipA lipB deletion mutant was more sensitive than the wild-type parent strain to killing by human lysozyme in the presence of human apolactoferrin. This is the first report of the production of lysozyme inhibitors by M. catarrhalis.

Identification of vaccine antigens using integrated proteomic analyses of surface immunogens from serogroup B Neisseria meningitidis

Meningococcal surface proteins capable of evoking a protective immune response are candidates for inclusion in protein-based vaccines against serogroup B Neisseria meningitidis (NmB). In this study, a 2-dimensional (2-D) gel-based platform integrating surface and immune-proteomics was developed to characterize NmB surface protein antigens. The surface proteome was analyzed by differential 2-D gel electrophoresis following treatment of live bacteria with proteinase K. Alongside, proteins recognized by immune sera from mice challenged with live meningococci were detected using 2-D immunoblots. In combination, seventeen proteins were identified including the well documented antigens PorA, OpcA and factor H-binding protein, previously reported potential antigens and novel potential immunogens. Results were validated for the macrophage infectivity potentiator (MIP), a recently proposed NmB vaccine candidate. MIP-specific antisera bound to meningococci in whole-cell ELISA and facilitated opsonophagocytosis and deposition of complement factors on the surface of meningococcal isolates of different serosubtypes. Cleavage by proteinase K was confirmed in western blots and shown to occur in a fraction of the MIP expressed by meningococci suggesting transient or limited surface exposure. These observations add knowledge for the development of a protein NmB vaccine. The proteomic workflow presented here may be used for the discovery of vaccine candidates against other pathogens.

BIOLOGICAL SIGNIFICANCE

This study presents an integrated proteomic strategy to identify proteins from N. meningitidis with desirable properties (i.e. surface exposure and immunogenicity) for inclusion in subunit vaccines against bacterial meningitis. The effectiveness of the method was demonstrated by the identification of some of the major meningococcal vaccine antigens. Information was also obtained about novel potential immunogens as well as the recently described potential antigen macrophage infectivity potentiator which can be useful for its consideration as a vaccine candidate. Additionally, the proteomic strategy presented in this study provides a generic 2-D gel-based platform for the discovery of vaccine candidates against other bacterial infections.

Identification of the immunoproteome of the meningococcus by cell surface immunoprecipitation and MS

Most healthy adults are protected from meningococcal disease by the presence of naturally acquired anti-meningococcal antibodies; however, the identity of the target antigens of this protective immunity remains unclear, particularly for protection against serogroup B disease. To identify the protein targets of natural protective immunity we developed an immunoprecipitation and proteomics approach to define the immunoproteome of the meningococcus. Sera from 10 healthy individuals showing serum bactericidal activity against both a meningococcal C strain (L91543) and the B strain MC58, together with commercially available pooled human sera, were used as probe antisera. Immunoprecipitation was performed with each serum sample and live cells from both meningococcal strains. Immunoprecipitated proteins were identified by MS. Analysis of the immunoproteome from each serum demonstrated both pan-reactive antigens that were recognized by most sera as well as subject-specific antigens. Most antigens were found in both meningococcal strains, but a few were strain-specific. Many of the immunoprecipitated proteins have been characterized previously as surface antigens, including adhesins and proteases, several of which have been recognized as vaccine candidate antigens, e.g. factor H-binding protein, NadA and neisserial heparin-binding antigen. The data demonstrate clearly the presence of meningococcal antibodies in healthy individuals with no history of meningococcal infection and a wide diversity of immune responses. The identification of the immunoreactive proteins of the meningococcus provides a basis for understanding the role of each antigen in the natural immunity associated with carriage and may help to design vaccination strategies.

The biology of Neisseria adhesins

Members of the genus Neisseria include pathogens causing important human diseases such as meningitis, septicaemia, gonorrhoea and pelvic inflammatory disease syndrome. Neisseriae are found on the exposed epithelia of the upper respiratory tract and the urogenital tract. Colonisation of these exposed epithelia is dependent on a repertoire of diverse bacterial molecules, extending not only from the surface of the bacteria but also found within the outer membrane. During invasive disease, pathogenic Neisseriae also interact with immune effector cells, vascular endothelia and the meninges. Neisseria adhesion involves the interplay of these multiple surface factors and in this review we discuss the structure and function of these important molecules and the nature of the host cell receptors and mechanisms involved in their recognition. We also describe the current status for recently identified Neisseria adhesins. Understanding the biology of Neisseria adhesins has an impact not only on the development of new vaccines but also in revealing fundamental knowledge about human biology.

Immunization with recombinant Chaperonin60 (Chp60) outer membrane protein induces a bactericidal antibody response against Neisseria meningitidis

Sera from individuals colonized with Neisseria meningitidis and from patients with meningococcal disease contain antibodies specific for the neisserial heat-shock/chaperonin (Chp)60 protein. In this study, immunization of mice with recombinant (r)Chp60 in saline; adsorbed to aluminium hydroxide; in liposomes and detergent micelles, with and without the adjuvant MonoPhosphoryl Lipid A (MPLA), induced high and similar (p>0.05) levels of antibodies that recognized Chp60 in outer membranes (OM). FACS analysis and immuno-fluorescence experiments demonstrated that Chp60 was surface-expressed on meningococci. By western blotting, murine anti-rChp60 sera recognized a protein of Mr 60kDa in meningococcal cell lysates. However, cross-reactivity with human HSP60 protein was also observed. By comparing translated protein sequences of strains, 40 different alleles were found in meningococci in the Bacterial Isolate Genome Sequence database with an additional 5 new alleles found in our selection of 13 other strains from colonized individuals and patients. Comparison of the non-redundant translated amino acid sequences from all the strains revealed ≥97% identity between meningococcal Chp60 proteins, and in our 13 strains the protein was expressed to high and similar levels. Bactericidal antibodies (median reciprocal titres of 32-64) against the homologous strain MC58 were induced by immunization with rChp60 in liposomes, detergent micelles and on Al(OH)3. Bactericidal activity was influenced by the addition of MPLA and the delivery formulation used. Moreover, the biological activity of anti-Chp60 antisera did not extend significantly to heterologous meningococcal strains. Thus, in order to provide broad coverage, vaccines based on Chp60 would require multiple proteins and specific bactericidal epitope identification.