Reverse vaccinology-based identification of a novel surface lipoprotein that is an effective vaccine antigen against bovine infections caused by Pasteurella multocida.

Pasteurella multocida can infect a multitude of wild and domesticated animals, with infections in cattle resulting in hemorrhagic septicemia (HS) or contributing to bovine respiratory disease (BRD) complex. Current cattle vaccines against P. multocida consist of inactivated bacteria, which only offer limited and serogroup specific protection. Here, we describe a newly identified surface lipoprotein, PmSLP, that is present in nearly all annotated P. multocida strains isolated from cattle. Bovine associated variants span three of the four identified phylogenetic clusters, with PmSLP-1 and PmSLP-2 being restricted to BRD associated isolates and PmSLP-3 being restricted to isolates associated with HS. Recombinantly expressed, soluble PmSLP-1 (BRD-PmSLP) and PmSLP-3 (HS-PmSLP) vaccines were both able to provide full protection in a mouse sepsis model against the matched P. multocida strain, however no cross-protection and minimal serum IgG cross-reactivity was identified. Full protection against both challenge strains was achieved with a bivalent vaccine containing both BRD-PmSLP and HS-PmSLP, with serum IgG from immunized mice being highly reactive to both variants. Year-long stability studies with lyophilized antigen stored under various temperatures show no appreciable difference in biophysical properties or loss of efficacy in the mouse challenge model. PmSLP-1 and PmSLP-3 vaccines were each evaluated for immunogenicity in two independent cattle trials involving animals of different age ranges and breeds. In all four trials, vaccination with PmSLP resulted in an increase in antigen specific serum IgG over baseline. In a blinded cattle challenge study with a recently isolated HS strain, the matched HS-PmSLP vaccine showed strong efficacy (75-87.5% survival compared to 0% in the control group). Together, these data suggest that cattle vaccines composed of PmSLP antigens can be a practical and effective solution for preventing HS and BRD related P. multocida infections.

A Slam-dependent hemophore contributes to heme acquisition in the bacterial pathogen Acinetobacter baumannii.

Nutrient acquisition systems are often crucial for pathogen growth and survival during infection, and represent attractive therapeutic targets. Here, we study the protein machinery required for heme uptake in the opportunistic pathogen Acinetobacter baumannii. We show that the hemO locus, which includes a gene encoding the heme-degrading enzyme, is required for high-affinity heme acquisition from hemoglobin and serum albumin. The hemO locus includes a gene coding for a heme scavenger (HphA), which is secreted by a Slam protein. Furthermore, heme uptake is dependent on a TonB-dependent receptor (HphR), which is important for survival and/or dissemination into the vasculature in a mouse model of pulmonary infection. Our results indicate that A. baumannii uses a two-component receptor system for the acquisition of heme from host heme reservoirs.

Development of a non-biased, high-throughput ELISA for the rapid evaluation of immunogenicity and cross-reactivity.

Traditional ELISA-based protein analysis has been predicated on the assumption that proteins bind randomly to the solid surface of the ELISA plate polymer (polystyrene or polyvinyl chloride). Random adherence to the plate ensures equal access to all faces of the protein, an important consideration when evaluating immunogenicity of polyclonal serum samples as well as when examining the cross-reactivity of immune serum against different antigenic variants of a protein. In this study we demonstrate that the soluble form of the surface lipoprotein transferrin binding protein B (TbpB) from three different bacterial pathogens (Neisseria meningitidis, Actinobacillus pleuropneumoniae, and Mannheimia haemolytica) bind the ELISA plate in a manner that consistently obscures the transferrin binding face of the proteins' N-lobe. In order to develop a non-biased ELISA where all faces of the protein are accessible, the strong interaction between biotin and avidin has been exploited by adding a biotin tag to these proteins during Escherichia coli-based cytoplasmic expression and utilizing streptavidin or neutravidin coated ELISA plates for protein capture and display. The use of avidin coated ELISA plates also allows for rapid purification of biotin-tagged proteins from crude E. coli lysates, removing the requirement of prior affinity purification of each protein to be included in the ELISA-based analyses. In proof of concept experiments we demonstrate the utility of this approach for evaluating immunogenicity and cross-reactivity of serum from mice and pigs immunized with TbpBs from human and porcine pathogens.

Utility of Hybrid Transferrin Binding Protein Antigens for Protection Against Pathogenic Neisseria Species.

The surface transferrin receptor proteins from Neisseria gonorrhoeae have been recognized as ideal vaccine targets due to their critical role in survival in the human male genitourinary tract. Recombinant forms of the surface lipoprotein component of the receptor, transferrin binding protein B (TbpB), can be readily produced at high levels in the Escherichia coli cytoplasm and is suitable for commercial vaccine production. In contrast, the integral outer membrane protein, transferrin binding protein A (TbpA), is produced at relatively low levels in the outer membrane and requires detergents for solubilization and stabilization, processes not favorable for commercial applications. Capitalizing on the core ß-barrel structural feature common to the lipoprotein and integral outer membrane protein we engineered the lipoprotein as a scaffold for displaying conserved surface epitopes from TbpA. A stable version of the C-terminal domain of TbpB was prepared by replacing four larger exposed variable loops with short linking peptide regions. Four surface regions from the plug and barrel domains of Neisseria TbpA were transplanted onto this TbpB C-lobe scaffold, generating stable hybrid antigens. Antisera generated in mice and rabbits against the hybrid antigens recognized TbpA at the surface of Neisseria meningitidis and inhibited transferrin-dependent growth at levels comparable or better than antisera directed against the native TbpA protein. Two of the engineered hybrid antigens each elicited a TbpA-specific bactericidal antibody response comparable to that induced by TbpA. A hybrid antigen generated using a foreign scaffold (TbpB from the pig pathogen Haemophilus parasuis) displaying neisserial TbpA loop 10 was evaluated in a model of lower genital tract colonization by N. gonorrhoeae and a model of invasive infection by N. meningitidis. The loop 10 hybrid antigen was as effective as full length TbpA in eliminating N. gonorrhoeae from the lower genital tract of female mice and was protective against the low dose invasive infection by N. meningitidis. These results demonstrate that TbpB or its derivatives can serve as an effective scaffold for displaying surface epitopes of integral outer membrane antigens and these antigens can elicit protection against bacterial challenge.

Murine host response to Neisseria gonorrhoeae upper genital tract infection reveals a common transcriptional signature, plus distinct inflammatory responses that vary between reproductive cycle phases.

BACKGROUND: The emergence of fully antimicrobial resistant Neisseria gonorrhoeae has led global public health agencies to identify a critical need for next generation anti-gonococcal pharmaceuticals. The development and success of these compounds will rely upon valid pre-clinical models of gonorrhoeae infection. We recently developed and reported the first model of upper genital tract gonococcal infection. During initial characterization, we observed significant reproductive cycle-based variation in infection outcome. When uterine infection occurred in the diestrus phase, there was significantly greater pathology than during estrus phase. The aim of this study was to evaluate transcriptional profiles of infected uterine tissue from mice in either estrus or diestrus phase in order to elucidate possible mechanisms for these differences. RESULTS: Genes and biological pathways with phase-independent induction during infection showed a chemokine dominant cytokine response to Neisseria gonorrhoeae. Despite general induction being phase-independent, this common anti-gonococcal response demonstrated greater induction during diestrus phase infection. Greater activity of granulocyte adhesion and diapedesis regulators during diestrus infection, particularly in chemokines and diapedesis regulators, was also shown. In addition to a greater induction of the common anti-gonococcal response, Gene Set Enrichment Analysis identified a diestrus-specific induction of type-1 interferon signaling pathways. CONCLUSIONS: This transcriptional analysis of murine uterine gonococcal infection during distinct points in the natural reproductive cycle provided evidence for a common anti-gonococcal response characterized by significant induction of granulocyte chemokine expression and high proinflammatory mediators. The basic biology of this host response to N. gonorrhoeae in estrus and diestrus is similar at the pathway level but varies drastically in magnitude. Overlaying this, we observed type-1 interferon induction specifically in diestrus infection where greater pathology is observed. This supports recent work suggesting this pathway has a significant, possibly host-detrimental, function in gonococcal infection. Together these findings lay the groundwork for further examination of the role of interferons in gonococcal infection. Additionally, this work enables the implementation of the diestrus uterine infection model using the newly characterized host response as a marker of pathology and its prevention as a correlate of candidate vaccine efficacy and ability to protect against the devastating consequences of N. gonorrhoeae-associated sequelae.

Specific Binding to Differentially Expressed Human Carcinoembryonic Antigen-Related Cell Adhesion Molecules Determines the Outcome of Neisseria gonorrhoeae Infections along the Female Reproductive Tract.

The gonococcal Opa proteins are an antigenically variable family of surface adhesins that bind human carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1), CEACAM3, CEACAM5, and/or CEACAM6, cell surface glycoproteins that are differentially expressed on a broad spectrum of human cells and tissues. While they are presumed to be important for infection, the significance of various Opa-CEACAM-mediated cellular interactions in the context of the genital tract has remained unclear. Here, we observed that CEACAM1 and CEACAM5 are differentially expressed on epithelia lining the upper and lower portions of the human female genital tract, respectively. Using transgenic mouse lines expressing human CEACAMs in a manner that reflects this differential pattern, we considered the impact of Opa-CEACAM interactions during uncomplicated lower genital tract infections versus during pelvic inflammatory disease. Our results demonstrate that Opa-CEACAM5 binding on vaginal epithelia facilitates the long-term colonization of the lower genital tract, while Opa protein binding to CEACAM1 on uterine epithelia enhances gonococcal association and penetration into these tissues. While these Opa-dependent interactions with CEACAM-expressing epithelial surfaces promote infection, Opa binding by neutrophil-expressed CEACAMs counterbalances this by facilitating more effective gonococcal clearance. Furthermore, during uterine infections, CEACAM-dependent tissue invasion aggravates disease pathology by increasing the acute inflammatory response. Together, these findings demonstrate that the outcome of infection is determined by both the cell type-specific expression of human CEACAMs and the CEACAM specificity of the Opa variants expressed, which combine to determine the level of gonococcal association with the genital mucosa versus the extent of CEACAM-dependent inflammation and gonococcal clearance by neutrophils.

Global analysis of neutrophil responses to Neisseria gonorrhoeae reveals a self-propagating inflammatory program.

An overwhelming neutrophil-driven response causes both acute symptoms and the lasting sequelae that result from infection with Neisseria gonorrhoeae. Neutrophils undergo an aggressive opsonin-independent response to N. gonorrhoeae, driven by the innate decoy receptor CEACAM3. CEACAM3 is exclusively expressed by human neutrophils, and drives a potent binding, phagocytic engulfment and oxidative killing of Opa-expressing bacteria. In this study, we sought to explore the contribution of neutrophils to the pathogenic inflammatory process that typifies gonorrhea. Genome-wide microarray and biochemical profiling of gonococcal-infected neutrophils revealed that CEACAM3 engagement triggers a Syk-, PKCδ- and Tak1-dependent signaling cascade that results in the activation of an NF-κB-dependent transcriptional response, with consequent production of pro-inflammatory cytokines. Using an in vivo model of N. gonorrhoeae infection, we show that human CEACAM-expressing neutrophils have heightened migration toward the site of the infection where they may be further activated upon Opa-dependent binding. Together, this study establishes that the role of CEACAM3 is not restricted to the direct opsonin-independent killing by neutrophils, since it also drives the vigorous inflammatory response that typifies gonorrhea. By carrying the potential to mobilize increasing numbers of neutrophils, CEACAM3 thereby represents the tipping point between protective and pathogenic outcomes of N. gonorrhoeae infection.