Development and Evaluation of an Immunoinformatics-Based Multi-Peptide Vaccine against Acinetobacter baumannii Infection

Multi-drug-resistant (MDR) Acinetobacter baumannii is an opportunistic pathogen associated with hospital-acquired infections. Due to its environmental persistence, virulence, and limited treatment options, this organism causes both increased patient mortality and incurred healthcare costs. Thus, prophylactic vaccination could be ideal for intervention against MDR Acinetobacter infection in susceptible populations. In this study, we employed immunoinformatics to identify peptides containing both putative B- and T-cell epitopes from proteins associated with A. baumannii pathogenesis. A novel Acinetobacter Multi-Epitope Vaccine (AMEV2) was constructed using an A. baumannii thioredoxin A (TrxA) leading protein sequence followed by five identified peptide antigens. Antisera from A. baumannii infected mice demonstrated reactivity to rAMEV2, and subcutaneous immunization of mice with rAMEV2 produced high antibody titer against the construct as well as peptide components. Immunization results in increased frequency of IL-4-secreting splenocytes indicative of a Th2 response. AMEV2-immunized mice were protected against intranasal challenge with a hypervirulent strain of A. baumannii and demonstrated reduced bacterial burden at 48 h. In contrast, all mock vaccinated mice succumbed to infection within 3 days. Results presented here provide insight into the effectiveness of immunoinformatic-based vaccine design and its potential as an effective strategy to combat the rise of MDR pathogens.

Thioredoxin-mediated alteration of protein content and cytotoxicity of Acinetobacter baumannii outer membrane vesicles

Acinetobacter baumannii is a Gram-negative bacterium responsible for many hospital-acquired infections including ventilator-associated pneumonia and sepsis. We have previously identified A. baumannii thioredoxin A protein (TrxA) as a virulence factor with a multitude of functions including reduction of protein disulfides. TrxA plays an important role in resistance to oxidative stress facilitating host immune evasion in part by alteration of type IV pili and cell surface hydrophobicity. Other virulence factors such as outer membrane vesicles (OMV) shed by bacteria have been shown to mediate bacterial intercellular communication and modulate host immune response. To investigate whether OMVs can be modulated by TrxA, we isolated OMVs from wild type (WT) and TrxA-deficient (ΔtrxA) A. baumannii clinical isolate Ci79 and carried out a functional and proteomic comparison. Despite attenuation of ΔtrxA in a mouse challenge model, pulmonary inoculation of ΔtrxA OMVs resulted in increased lung permeability compared to WT OMVs. Furthermore, ΔtrxA OMVs induced more J774 macrophage-like cell death than WT OMVs. This ΔtrxA OMV-mediated cell death was abrogated when cells were incubated with protease-K-treated OMVs suggesting OMV proteins were responsible for cytotoxicity. We therefore compared WT and mutant OMV proteins using proteomic analysis. We observed that up-regulated and unique ΔtrxA OMV proteins consisted of many membrane bound proteins involved in small molecule transport as well as proteolytic activity. Bacterial OmpA, metalloprotease, and fimbrial protein have been shown to enhance mammalian cell apoptosis through various mechanisms. Differential packaging of these proteins in ΔtrxA OMVs may contribute to the increased cytotoxicity observed in this study.

Modulation of Immune Response to Chlamydia muridarum by Host miR-135a

Previously, our laboratory established the role of small, noncoding RNA species, i.e., microRNA (miRNA) including miR-135a in anti-chlamydial immunity in infected hosts. We report here chlamydial infection results in decreased miR-135a expression in mouse genital tissue and a fibroblast cell line. Several chemokine and chemokine receptor genes (including CXCL10, CCR5) associated with chlamydial pathogenesis were identified in silico to contain putative miR-135a binding sequence(s) in the 3' untranslated region. The role of miR-135a in the host immune response was investigated using exogenous miR-135a mimic to restore the immune phenotype associated with decreased miR-135a following Chlamydia muridarum (Cm) infection. We observed miR-135a regulation of Cm-primed bone marrow derived dendritic cells (BMDC) via activation of Cm-immune CD4⁺ T cells for clonal expansion and CCR5 expression. Using a transwell cell migration assay, we explore the role of miR-135a in regulation of genital tract CXCL10 expression and recruitment of CXCR3⁺ CD4⁺ T cells via the CXCL10/CXCR3 axis. Collectively, data reported here support miR-135a affecting multiple cellular processes in response to chlamydial infection.

The Role of MicroRNA-155 in Chlamydia muridarum Infected lungs

Our laboratory has investigated the role of an evolutionarily conserved RNA species called microRNAs (miRs) in regulation of anti-chlamydial protective immunity. MiRs including miR-155 expressed in specific immune effector cells are critical for antigen specific protective immunity and IFN-γ production. Using miR-155 deficient mice, and a murine pulmonary model for chlamydial infection, we report here 1) the effect of host miR-155 on bacterial burden, and 2) identify probable immune genes regulated by miR-155.

Thioredoxin Modulates Cell Surface Hydrophobicity in Acinetobacter baumannii

Acinetobacter baumannii, a Gram-negative coccobacillus, has become a prevalent nosocomial health threat affecting the majority of hospitals both in the U.S. and around the globe. Microbial cell surface hydrophobicity (CSH) has previously been correlated with virulence, uptake by immune cells, and attachment to epithelial cells. A mutant strain of A. baumannii (ΔtrxA) lacking the redox protein thioredoxin A was found to be more hydrophobic than its wild type (WT) and complemented counterparts, as measured by both Microbial Adhesion to Hydrocarbon (MATH) and salt aggregation. The hydrophobicity of the mutant could be abrogated through treatment with sodium cyanoborohydride (SCBH). This modulation correlated with reduction of disulfide bonds, as SCBH was able to reduce 5,5′-dithio-bis-[2-nitrobenzoic acid] and treatment with the known disulfide reducer, β-mercaptoethanol, also decreased ΔtrxA CSH. Additionally, the ΔtrxA mutant was more readily taken up than WT by J774 macrophages and this differential uptake could be abrogated though SCBH treatment. When partitioned into aqueous and hydrophobic phases, ΔtrxA recovered from the hydrophobic partition was phagocytosed more readily than from the aqueous phase further supporting the contribution of CSH to A. baumannii uptake by phagocytes. A second Gram-negative bacterium, Francisella novicida, also showed the association of TrxA deficiency (FnΔtrxA) with increased hydrophobicity and uptake by J774 cells. We previously have demonstrated that modification of the type IV pilus system (T4P) was associated with the A. baumannii ΔtrxA phenotype, and the Francisella FnΔtrxA mutant also was found to have a marked T4P deficiency. Interestingly, a F. novicida mutant lacking pilT also showed increased hydrophobicity over FnWT. Collective evidence presented in this study suggests that Gram-negative bacterial thioredoxin mediates CSH through multiple mechanisms including disulfide-bond reduction and T4P modulation.

Thioredoxin-A is a virulence factor and mediator of the type IV pilus system in Acinetobacter baumannii

The Gram-negative pathogen, Acinetobacter baumannii has emerged as a global nosocomial health threat affecting the majority of hospitals in the U.S. and abroad. The redox protein thioredoxin has been shown to play several roles in modulation of cellular functions affecting various virulence factors in Gram-negative pathogens. This study aims to explore the role of thioredoxin-A protein (TrxA) in A. baumannii virulence. We determined that deletion of the TrxA gene did not significantly affect resistance to environmental stressors such as temperature, salt, and pH. However, TrxA was critical for survival in the presence of elevated levels of hydrogen peroxide. Lack of TrxA was associated with decreased expression of type IV pili related genes and an inability to undergo normal twitching motility. Interestingly, the TrxA-null mutant was able to form biofilms better than the wildtype (WT) and was observed to be significantly less virulent than the WT in a pulmonary infection model. These results are supportive of thioredoxin playing a key role in A. baumannii virulence.

Role of Acinetobacter baumannii thioredoxin in pulmonary bacterial dissemination following LPS induced lung injury

Despite medical advances, sepsis remains an increasing and major cause of death in hospitalized patients in the United States. Multiple-drug resistant Acinetobacter baumannii has emerged as an important hospital-acquired pathogen in both pulmonary infections and sepsis. Previously, our lab has shown the importance of bacterial thioredoxin during infection. A TrxA-null mutant (ΔTrxA) generated from A. baumannii Clinical isolate 79 (Ci79) showed a 100-fold decrease in virulence during systemic challenge. To further define the role of thioredoxin, our lab has created a pulmonary model of infection that leads to sepsis and death in C57BL/6 mice. This model is dependent on the induction of acute lung injury through E. coli lipopolysaccharide (LPS) injection. Lungs were analyzed for increased permeability using FITC-labeled dextran. Mice receiving the LPS showed significantly higher FITC-dextran particles in their serum compared to those that did not. Additionally, histopathology and cytokine production indicated limited immune response to the dose of LPS used. Using this model, mice showed significantly increased WT organ burdens in the lungs, liver, kidneys, cervical lymph nodes, and spleen compared to the mutant. Concurrently, mortality was significantly greater in the WT compared to ΔTrxA (~85%). Histopathological assessment showed increased cellular infiltrates and pulmonary inflammation during WT vs ΔTrxA infection. Finally, when the WT was treated with a thioredoxin blocker (PX-12) before challenge, mice survival improved from ~15% to ~75% with treatment. Together, this data demonstrates that thioredoxin plays a vital role in dissemination and virulence and could be a potential target to attenuate sepsis.

Microbial co-infection alters macrophage polarization, phagosomal escape, and microbial killing

Macrophages are important innate immune cells that respond to microbial insults. In response to multi-bacterial infection, the macrophage activation state may change upon exposure to nascent mediators, which results in different bacterial killing mechanism(s). In this study, we utilized two respiratory bacterial pathogens, Mycobacterium bovis (Bacillus Calmette Guẻrin, BCG) and Francisella tularensis live vaccine strain (LVS) with different phagocyte evasion mechanisms, as model microbes to assess the influence of initial bacterial infection on the macrophage response to secondary infection. Non-activated (M0) macrophages or activated M2-polarized cells (J774 cells transfected with the mouse IL-4 gene) were first infected with BCG for 24–48 h, subsequently challenged with LVS, and the results of inhibition of LVS replication in the macrophages was assessed. BCG infection in M0 macrophages activated TLR2-MyD88 and Mincle-CARD9 signaling pathways, stimulating nitric oxide (NO) production and enhanced killing of LVS. BCG infection had little effect on LVS escape from phagosomes into the cytosol in M0 macrophages. In contrast, M2-polarized macrophages exhibited enhanced endosomal acidification, as well as inhibiting LVS replication. Pre-infection with BCG did not induce NO production and thus did not further reduce LVS replication. This study provides a model for studies of the complexity of macrophage activation in response to multi-bacterial infection.

Vaccination with a live attenuated Acinetobacter baumannii deficient in thioredoxin provides protection against systemic Acinetobacter infection

Multi-drug resistant Acinetobacter baumannii (MDR-Ab), an opportunistic pathogen associated with nosocomial and combat related infections, has a high mortality due to its virulence and limited treatment options. Deletion of the thioredoxin gene (TrxA) from a clinical isolate of MDR-Ab resulted in a 100-fold increase in 50% lethal dose (LD₅₀) in a systemic challenge murine model. Thus, we investigated the potential use of this attenuated strain as a live vaccine against MDR-Ab. Mice were vaccinated by subcutaneous (s.c.) injection of 2×10⁵ CFU of the ΔtrxA mutant, boosted 14days later with an equivalent inoculum, and then challenged 30days post-vaccination by i.p. injection with 10 LD₅₀ of the wild type (WT) Ci79 strain. Efficacy of vaccination was evaluated by monitoring MDR-Ab specific antibody titers and cytokine production, observing pathology and organ burdens after WT challenge, and measuring levels of serum pentraxin-3, a molecular correlate of A. baumannii infection severity, before and after challenge. Mice vaccinated with ΔtrxA were fully protected against the lethal challenge of WT. However, minimal immunoglobulin class switching was observed with IgM predominating. Spleens harvested from vaccinated mice exhibited negligible levels of IL-4, IFN-γ and IL-17 production when stimulated with UV-inactivated WT Ci79. Importantly, tissues obtained from vaccinated mice displayed reduced pathology and organ burden compared to challenged non-vaccinated mice. Additionally, serum pentraxin-3 concentrations were not increased 24h after challenge in vaccinated mice, correlating with reduction of WT MDR-Ab infection in ΔtrxA immunized mice. Furthermore, passive immunization with ΔtrxA-immune sera provided protection against lethal systemic Ci79 challenge. Collectively, the defined live attenuated ΔtrxA strain is a vaccine candidate against emerging MDR Acinetobacter infection.

Role of Acinetobacter baumannii thioredoxin in bacterial dissemination by modulation of mucosal oxidative homeostasis

Acinetobacter baumannii is an increasing cause of hospital-acquired infections and a prominent cause of combat-related infections in the Middle East. Infections with this bacterium lead to a TLR4 response that initiates a potent innate immune response. Bacterial coinfection may occur in hospitalized patients, and endotoxin (LPS) released from one Gram-negative bacterium may have profound effects on pathogenesis of other co-infecting bacteria. Specifically, LPS induced oxidative stress has a significant impact on mucosal barrier function, leading to enhanced permeability and bacterial translocation. To delineate the importance of LPS in E. coli and Ab coinfection, we utilized a murine model of pulmonary Ab infection with oxidative stress induced via LPS injection. While the bacterial factors involved in translocation under oxidative stress are largely unknown, one plausible factor, based on previous research in our lab, is thioredoxin. Thioredoxin-1 (Trx1/TrxA) is a member of the thioredoxin protein superfamily that can be reversibly oxidized and reduced to facilitate reduction of disulfide bonds, as well as for protecting against free-radical damage. Our lab has created a mutant of Ab Clinical isolate 79 (Ci79) that lacks thioredoxin-1 (ΔTrxA). Using this mutant, the effects of thioredoxin on bacterial translocation during oxidative stress can be determined. Mice given E. coli LPS showed significantly increased translocation of Ci79 via organ burden. Mice infected with ΔTrxA showed significantly less translocation than the WT strains. Additionally, when Ci79 was treated with a TrxA blocker before infection, survival was increased and organ burden decreased.

Chlamydial protease-like activity factor mediated protection against C. trachomatis in guinea pigs

We have comprehensively demonstrated using the mouse model that intranasal immunization with recombinant chlamydial protease-like activity factor (rCPAF) leads to a significant reduction in bacterial burden, genital tract pathology and preserves fertility following intravaginal genital chlamydial challenge. In the present report, we evaluated the protective efficacy of rCPAF immunization in guinea pigs, a second animal model for genital chlamydial infection. Using a vaccination strategy similar to the mouse model, we intranasally immunized female guinea pigs with rCPAF plus CpG deoxynucleotides (CpG; as an adjuvant), and challenged intravaginally with C. trachomatis serovar D (CT-D). Immunization with rCPAF/CpG significantly reduced vaginal CT-D shedding and induced resolution of infection by day 24, compared to day 33 in CpG alone treated and challenged animals. Immunization induced robust anti-rCPAF serum IgG 2 weeks following the last immunization, and was sustained at a high level 4 weeks post challenge. Upregulation of antigen specific IFN-γ gene expression was observed in rCPAF/CpG vaccinated splenocytes. Importantly, a significant reduction in inflammation in the genital tissue in rCPAF/CpG-immunized guinea pigs compared to CpG-immunized animals was observed. Taken together, this study provides evidence of the protective efficacy of rCPAF as a vaccine candidate in a second animal model of genital chlamydial infection.

Antigen specific immune response in Chlamydia muridarum genital infection is dependent on murine microRNAs-155 and -182

Anti-chlamydial immunity involves efficient presentation of antigens (Ag) to effector cells resulting in Ag-specific immune responses. There is limited information on inherent underlying mechanisms regulating these events. Previous studies from our laboratory have established that select microRNAs (miRs) function as molecular regulators of immunity in Chlamydia muridarum (Cm) genital infection. In this report, we investigated immune cell type-specific miRs, i.e. miR-155 and -182, and the role in Ag-specific immunity. We observed significant up-regulation of miR-155 in C57BL/6 bone marrow derived dendritic cells (BMDC), and miR-182 in splenic Ag-specific CD4+ T-cells. Using mimics and inhibitors, we determined that miR-155 contributed to BMDC activation following Cm infection. Co-cultures of miR-155 over-expressed in BMDC and miR-182 over-expressed in Ag-specific CD4+ T-cells, or miR-155-/- BMDC with miR-182 inhibitor treated Ag-specific CD4+ T-cells, resulted in IFN-γ production comparable to Ag-specific CD4+ T-cells isolated from Cm infected mice. Additionally, miR-182 was significantly up-regulated in intranasally vaccinated mice protected against Cm infection. In vivo depletion of miR-182 resulted in reduction in Ag-specific IFN-γ and genital pathology in Cm infected mice. To the best of our knowledge, this is the first study to report an interaction of miR-155 (in Cm infected DC) and miR-182 (in CD4+ T-cell) resulting in Ag specific immune responses against genital Cm.

Contribution of FcɛRI-associated vesicles to mast cell-macrophage communication following Francisella tularensis infection

Understanding innate immune intercellular communication following microbial infection remains a key biological issue. Using live cell imaging, we demonstrate that mast cells actively extend cellular projections to sample the macrophage periphery during Francisella tularensis LVS infection. Mast cell MHCII(hi) expression was elevated from less than 1% to 13% during LVS infection. Direct contact during co-culture with macrophages further increased mast cell MHCII(hi) expression to approximately 87%. Confocal analyses of the cellular perimeter revealed mast cell caspase-1 was localized in close proximity with FcɛRI in uninfected mast cells, and repositioned to clustered regions upon LVS infection. Importantly, mast cell FcɛRI-encompassed vesicles are transferred to macrophages by trogocytosis, and macrophage caspase-1 expression is further up-regulated upon direct contact with mast cells. Our study reveals direct cellular interactions between innate cells that may impact the function of caspase-1, a known sensor of microbial danger and requirement for innate defense against many pathogenic microbes including F. tularensis.

M-Cells Contribute to the Entry of an Oral Vaccine but Are Not Essential for the Subsequent Induction of Protective Immunity against Francisella tularensis

M-cells (microfold cells) are thought to be a primary conduit of intestinal antigen trafficking. Using an established neutralizing anti-RANKL (Receptor Activator of NF-κB Ligand) antibody treatment to transiently deplete M-cells in vivo, we sought to determine whether intestinal M-cells were required for the effective induction of protective immunity following oral vaccination with ΔiglB (a defined live attenuated Francisella novicida mutant). M-cell depleted, ΔiglB-vaccinated mice exhibited increased (but not significant) morbidity and mortality following a subsequent homotypic or heterotypic pulmonary F. tularensis challenge. No significant differences in splenic IFN-γ, IL-2, or IL-17 or serum antibody (IgG1, IgG2a, IgA) production were observed compared to non-depleted, ΔiglB-vaccinated animals suggesting complementary mechanisms for ΔiglB entry. Thus, we examined other possible routes of gastrointestinal antigen sampling following oral vaccination and found that ΔiglB co-localized to villus goblet cells and enterocytes. These results provide insight into the role of M-cells and complementary pathways in intestinal antigen trafficking that may be involved in the generation of optimal immunity following oral vaccination.

Guinea pig genital tract lipidome reveals in vivo and in vitro regulation of phosphatidylcholine 16:0/18:1 and contribution to Chlamydia trachomatis serovar D infectivity

INTRODUCTION

Chlamydia trachomatis (Ct), is the leading cause of sexually transmitted infections worldwide. Host transcriptomic- or proteomic profiling studies have identified key molecules involved in establishment of Ct infection or the generation of anti Ct-immunity. However, the contribution of the host metabolome is not known.

OBJECTIVES

The objective of this study was to determine the contribution of host metabolites in genital Ct infection.

METHODS

We used high-performance liquid chromatography-mass spectrometry, and mapped lipid profiles in genital swabs obtained from female guinea pigs at days 3, 9, 15, 30 and 65 post Ct serovar D intravaginal infection.

RESULTS

Across all time points assessed, 13 distinct lipid species including choline, ethanolamine and glycerol were detected. Amongst these metabolites, phosphatidylcholine (PC) was the predominant phospholipid detected from animals actively shedding bacteria i.e., at 3, 9, and 15 days post infection. However, at days 30 and 65 when the animals had cleared the infection, PC was observed to be decreased compared to previous time points. Mass spectrometry analyses of PC produced in guinea pigs (in vivo) and 104C1 guinea pig cell line (in vitro) revealed distinct PC species following Ct D infection. Amongst these, PC 16:0/18:1 was significantly upregulated following Ct D infection (p < 0.05, >twofold change) in vivo and in vitro infection models investigated in this report. Exogenous addition of PC 16:0/18:1 resulted in significant increase in Ct D in Hela 229 cells.

CONCLUSION

This study demonstrates a role for host metabolite, PC 16:0/18:1 in regulating genital Ct infection in vivo and in vitro.

IgA modulates respiratory dysfunction as a sequela to pulmonary chlamydial infection as neonates

Neonatal Chlamydia lung infections are associated with serious sequelae such as asthma and airway hyper-reactivity in children and adults. Our previous studies demonstrated the importance of Th-1 type cytokines, IL-12 and IFN-γ in protection against neonatal pulmonary chlamydial challenge; however, the role of the humoral arm of defense has not been elucidated. We hypothesized that B-cells and IgA, the major mucosal antibody, play a protective role in newborns against development of later life respiratory sequelae to Chlamydia infection. Our studies using neonatal mice revealed that all WT and IgA-deficient (IgA(-/-)) animals survived a sublethal pulmonary Chlamydia muridarum challenge at one day after birth with similar reduction in bacterial burdens over time. In contrast, all B-cell-deficient (μMT) mice succumbed to infection at the same challenge dose correlating to failure to control bacterial burdens in the lungs. Although IgA may not be important for bacterial clearance, we observed IgA(-/-) mice displayed greater respiratory dysfunction 5 weeks post challenge. Specifically, comparative respiratory functional analyses revealed a significant shift upward in P-V loops, and higher dynamic resistance in IgA(-/-) animals. This study provides insight(s) into the protective role of IgA in neonates against pulmonary chlamydial infection induced respiratory pathological sequelae observed later in life.

Macrophage migration inhibitory factor promotes resistance to glucocorticoid treatment in EAE

Objective:

Glucocorticoids (GCs) are used as standard treatment for acute attacks of multiple sclerosis (MS). However, GCs eventually lose efficacy and do not prevent disease progression. Macrophage migration inhibitory factor (MIF) is the only known proinflammatory cytokine induced by GCs that inhibits their anti-inflammatory effects. Therefore, we investigated whether MIF plays a role in resistance to GC treatment in experimental autoimmune encephalomyelitis (EAE), an animal model of MS.

Methods:

EAE was induced in wild-type (Wt) and MIF knockout (MIF^−/−) mice followed by treatment with dexamethasone (Dex) before or upon disease onset. Splenocytes and brain mononuclear cells were harvested for cytokine ELISPOT assay and flow cytometry analysis.

Results:

Treatment of EAE with Dex was substantially more efficacious in MIF^−/− mice than Wt mice. Dex treatment decreased MOG35-55–induced cytokine production by Wt or MIF^−/− CD4⁺ T cells only at the onset of EAE but inhibited upregulation of T-bet during acute and chronic phases of disease, particularly in MIF^−/− mice. Furthermore, passive EAE induced by adoptive transfer of T cells showed that Dex was highly effective in ameliorating disease induced by MIF^−/− CD4⁺ T cells but not by Wt CD4⁺ T cells. The expression of T-bet and VLA-4 was decreased in CD4⁺ T cells in MIF^−/− mice compared with Wt mice.

Conclusions:

Our data establish MIF as a key molecule in resistance of pathogenic CD4⁺ T cells to GC treatment in EAE and as a potential target to enhance the effectiveness of steroid treatment in neuroinflammatory disorders.

In vivo whole animal body imaging reveals colonization of Chlamydia muridarum to the lower genital tract at early stages of infection

PURPOSE

The leading cause of sexually transmitted bacterial infection is Chlamydia trachomatis. The aim of this study is to investigate the early events in colonization of this bacterium within the murine genital tract.

PROCEDURES

An in vivo animal body imaging technology was used to track fluorophore labeled C. muridarum elementary bodies (EBs) inoculated intravaginally in C57BL/6 mice during the first 24 h of infection.

RESULTS

Ascension of viable EBs was observed (1) to be localized to the lower regions of the murine genital tract within the first 24 h post challenge and (2) was dose independent during this early exposure period. Molecular detection revealed enhanced bacterial load in lower regions of the genital tract with increasing bacterial load in the upper region beginning 12 h post inoculation.

CONCLUSION

This study provides additional insight into chlamydial colonization in the murine genital tract during the first 12-24 h following inoculation.

Murine MicroRNA-214 regulates intracellular adhesion molecule (ICAM1) gene expression in genital Chlamydia muridarum infection

The hallmark of chlamydial infection is the development of upper genital pathology in the form of hydrosalpinx and oviduct and/or tubal dilatation. Although molecular events leading to genital tissue presentation and cellular architectural remodelling are unclear, early-stage host immune responses are believed to contribute to these long-term sequelae. Recently, we reported the contribution of selected infection-associated microRNAs (miRs) in the generation of host immunity at early-stage infection (day 6 after intravaginal Chlamydia muridarum challenge in C57BL/6 mice). In this report, we describe the contribution of an infection-associated microRNA, i.e. miR-214, to host immunity. Chlamydia muridarum infection in the C57BL/6 mouse genital tract significantly down-regulated miR-214 while up-regulating intracellular adhesion molecule 1 (ICAM1) gene expression. These in vivo observations were confirmed by establishing direct regulation of ICAM-1 by miR-214 in ex vivo genital cell cultures in the presence of miR-214 mimic and inhibitor. Because, ICAM-1 contributes to recruitment of neutrophils following infection, we also demonstrated that alteration of ICAM1 by miR-214 in interleukin-17A-deficient (IL-17A(-/-) ) mice correlated with reduction of neutrophils infiltrating genital tissue at day 6 after challenge. Additionally, these early-stage events resulted in significantly decreased genital pathology in IL-17A(-/-) mice compared with C57BL/6 mice. This report provides evidence for early-stage regulation of ICAM1 by microRNAs, resulting in reduction of genital pathology associated with chlamydial infection.

Use of a Guinea pig-specific transcriptome array for evaluation of protective immunity against genital chlamydial infection following intranasal vaccination in Guinea pigs

Guinea pigs have been used as a second animal model to validate putative anti-chlamydial vaccine candidates tested in mice. However, the lack of guinea pig-specific reagents has limited the utility of this animal model in Chlamydia sp. vaccine studies. Using a novel guinea pig-specific transcriptome array, we determined correlates of protection in guinea pigs vaccinated with Chlamydia caviae (C. caviae) via the intranasal route, previously reported by us and others to provide robust antigen specific immunity against subsequent intravaginal challenge. C. caviae vaccinated guinea pigs resolved genital infection by day 3 post challenge. In contrast, mock vaccinated animals continued to shed viable Chlamydia up to day 18 post challenge. Importantly, at day 80 post challenge, vaccinated guinea pigs experienced significantly reduced genital pathology - a sequelae of genital chlamydial infections, in comparison to mock vaccinated guinea pigs. Sera from vaccinated guinea pigs displayed antigen specific IgG responses and increased IgG1 and IgG2 titers capable of neutralizing GPIC in vitro. Th1-cellular/inflammatory immune genes and Th2-humoral associated genes were also found to be elevated in vaccinated guinea pigs at day 3 post-challenge and correlated with early clearance of the bacterium. Overall, this study provides the first evidence of guinea pig-specific genes involved in anti-chlamydial vaccination and illustrates the enhancement of the utility of this animal model in chlamydial pathogenesis.

Severe Acinetobacter baumannii sepsis is associated with elevation of pentraxin 3

Multidrug-resistant Acinetobacter baumannii is among the most prevalent bacterial pathogens associated with trauma-related wound and bloodstream infections. Although septic shock and disseminated intravascular coagulation have been reported following fulminant A. baumannii sepsis, little is known about the protective host immune response to this pathogen. In this study, we examined the role of PTX3, a soluble pattern recognition receptor with reported antimicrobial properties and stored within neutrophil granules. PTX3 production by murine J774a.1 macrophages was assessed following challenge with A. baumannii strains ATCC 19606 and clinical isolates (CI) 77, 78, 79, 80, and 86. Interestingly, only CI strains 79, 80, and 86 induced PTX3 synthesis in murine J774a.1 macrophages, with greatest production observed following CI 79 and 86 challenge. Subsequently, C57BL/6 mice were challenged intraperitoneally with CI 77 and 79 to assess the role of PTX3 in vivo. A. baumannii strain CI 79 exhibited significantly (P < 0.0005) increased mortality, with an approximate 50% lethal dose (LD50) of 10(5) CFU, while an equivalent dose of CI 77 exhibited no mortality. Plasma leukocyte chemokines (KC, MCP-1, and RANTES) and myeloperoxidase activity were also significantly elevated following challenge with CI 79, indicating neutrophil recruitment/activation associated with significant elevation in serum PTX3 levels. Furthermore, 10-fold-greater PTX3 levels were observed in mouse serum 12 h postchallenge, comparing CI 79 to CI 77 (1,561 ng/ml versus 145 ng/ml), with concomitant severe pathology (liver and spleen) and coagulopathy. Together, these results suggest that elevation of PTX3 is associated with fulminant disease during A. baumannii sepsis.

Enhancement of vaccine efficacy by expression of a TLR5 ligand in the defined live attenuated Francisella tularensis subsp. novicida strain U112ΔiglB::fljB

Oral vaccination with the defined live attenuated Francisella novicida vaccine strain U112ΔiglB has been demonstrated to induce protective immunity against pulmonary challenge with the highly human virulent Francisella tularensis strain SCHU S4. However, this vaccination regimen requires a booster dose in mice and Exhibits 50% protective efficacy in the Fischer 344 rat model. To enhance the efficacy of this vaccine strain, we engineered U112ΔiglB to express the Salmonella typhimurium FljB flagellin D1 domain, a TLR5 agonist. The U112ΔiglB::fljB strain was highly attenuated for intracellular macrophage replication, and although the FljB protein was expressed within the cytosol, it exhibited TLR5 activation in a TLR5-expressing HEK cell line. Additionally, infection of splenocytes and lymphocytes with U112ΔiglB::fljB induced significantly greater TNF-α production than infection with U112ΔiglB. Oral vaccination with U112ΔiglB::fljB also induced significantly greater protection than U112ΔiglB against pulmonary SCHU S4 challenge in rats. The enhanced protection was accompanied by higher IgG2a production and serum-mediated reduction of Francisella infectivity. Thus, the U112ΔiglB::fljB strain may serve as a potential vaccine candidate against pneumonic tularemia.

Chlamydia muridarum infection associated host MicroRNAs in the murine genital tract and contribution to generation of host immune response

PROBLEM

Chlamydia trachomatis (CT) is the leading sexually transmitted bacterial infection in humans and is associated with reproductive tract damage. However, little is known about the involvement and regulation of microRNAs (miRs) in genital CT.

METHODS

We analyzed miRs in the genital tract (GT) following C. muridarum (murine strain of CT) challenge of wild type (WT) and CD4(+) T-cell deficient (CD4(-/-)) C57BL/6 mice at days 6 and 12 post-challenge.

RESULTS

At day 6, miRs significantly downregulated in the lower GT were miR-125b-5p, -16, -214, -23b, -135a, -182, -183, -30c, and -30e while -146 and -451 were significantly upregulated, profiles not exhibited at day 12 post-bacterial challenge. Significant differences in miR-125b-5p (+5.06-fold change), -135a (+4.9), -183 (+7.9), and -182 (+3.2) were observed in C. muridarum-infected CD4(-/-) compared to WT mice. In silico prediction and mass spectrometry revealed regulation of miR-135a and -182 and associated proteins, that is, heat-shock protein B1 and alpha-2HS-glycoprotein.

CONCLUSION

This study provides evidence on regulation of miRs following genital chlamydial infection suggesting a role in pathogenesis and host immunity.

A T cell epitope-based vaccine protects against chlamydial infection in HLA-DR4 transgenic mice

Vaccination with recombinant chlamydial protease-like activity factor (rCPAF) has been shown to provide robust protection against genital Chlamydia infection. Adoptive transfer of IFN-γ competent CPAF-specific CD4⁺ T cells was sufficient to induce early resolution of chlamydial infection and reduction of subsequent pathology in recipient IFN-γ-deficient mice indicating the importance of IFN-γ secreting CD4⁺ T cells in host defense against Chlamydia. In this study, we identify CD4⁺ T cell reactive CPAF epitopes and characterize the activation of epitope-specific CD4⁺ T cells following antigen immunization or Chlamydia challenge. Using the HLA-DR4 (HLA-DRB1*0401) transgenic mouse for screening overlapping peptides that induced T cell IFN-γ production, we identified at least 5 CPAF T cell epitopes presented by the HLA-DR4 complex. Immunization of HLA-DR4 transgenic mice with a rCPAFep fusion protein containing these 5 epitopes induced a robust cell-mediated immune response and significantly accelerated the resolution of genital and pulmonary Chlamydia infection. rCPAFep vaccination induced CPAF-specific CD4⁺ T cells in the spleen were detected using HLA-DR4/CPAF-epitope tetramers. Additionally, CPAF-specific CD4⁺ clones could be detected in the mouse spleen following Chlamydia muridarum and a human Chlamydia trachomatis strain challenge using these novel tetramers. These results provide the first direct evidence that a novel CPAF epitope vaccine can provide protection and that HLA-DR4/CPAF-epitope tetramers can detect CPAF epitope-specific CD4⁺ T cells in HLA-DR4 mice following C. muridarum or C. trachomatis infection. Such tetramers could be a useful tool for monitoring CD4⁺ T cells in immunity to Chlamydia infection and in developing epitope-based human vaccines using the murine model.

Mast cells: multitalented facilitators of protection against bacterial pathogens

Mast cells are crucial effector cells evoking immune responses against bacterial pathogens. The positioning of mast cells at the host-environment interface, and the multitude of pathogen-recognition receptors and preformed mediator granules make these cells potentially the earliest to respond to an invading pathogen. In this review, the authors summarize the receptors used by mast cells to recognize invading bacteria and discuss the function of immune mediators released by mast cells in control of bacterial infection. The interaction of mast cells with other immune cells, including macrophages, dendritic cells and T cells, to induce protective immunity is highlighted. The authors also discuss mast cell-based vaccine strategies and the potential application in control of bacterial disease.

Vaginal chlamydial clearance following primary or secondary infection in mice occurs independently of TNF-α

The role of TNF-α in chlamydial clearance is uncertain. Antibody-mediated depletion of TNF-α in mice and guinea pigs has been shown not to significantly affect chlamydial clearance, whereas production of TNF-α in addition to IFN-γ from T cells has been shown to correlate with enhanced clearance. The aim of our study is to evaluate the mechanistic role of TNF-α in clearance of primary and secondary chlamydial infection from the genital tract (GT) using C57BL/6 TNF-α deficient (TNF-α^−/−) and wild type (WT) mice. Chlamydial shedding from the lower GT was evaluated following primary and secondary intravaginal challenge. Also, antibody and antigen specific cytokine responses were analyzed from the infected GT and spleens, and oviduct pathology determined to analyze the role of TNF-α in upper GT pathological sequelae. MHC II^−/− mice, known to display muted adaptive immune responses and failure to resolve genital chlamydial infections, were used as a negative control. Following both primary and secondary genital chlamydial infection, TNF-α^−/− mice exhibited elevated granzyme B production, but similar IFN-γ and antibody responses. Importantly, absence of TNF-α did not significantly alter the resolution of infection. However, TNF-α^−/− mice displayed significantly reduced upper genital tract (UGT) pathology compared to WT mice. This study demonstrates mechanistically that optimal chlamydial clearance following primary and secondary chlamydial genital infection can occur in the complete absence of TNF-α, and considered with the reduction of upper GT pathology in TNF-α^−/− mice, suggests that targeted induction of anti-chlamydial TNF-α responses by vaccination may be unnecessary, and moreover could be potentially pathogenic.

Comparison of bone marrow-derived and mucosal mast cells in controlling intramacrophage Francisella tularensis replication

Although the importance of mast cells (MCs) in response to allergens has been characterized extensively, the contribution of these cells in host defense against bacterial pathogens is not well understood. Previously, we have demonstrated that the release of interleukin-4 by bone marrow-derived MCs inhibits intramacrophage replication of Francisella tularensis live vaccine strain (LVS). Because pneumonic tularemia is one of the several manifestations of infection by Francisella, it is important to determine whether MCs present in mucosal tissues, i.e. the lung, exhibit similar effects on LVS replication. On the basis of this rationale, we phenotypically compared mucosal mast cells (MMCs) to traditional bone marrow-derived MCs. Both cell types exhibited similar levels of cell surface expression of fragment crystal epsilon receptor I (FcεRI), mast/stem cell growth factor receptor (c-Kit) and major histocompatibility complex I (MHCI), as well as patterns of granulation. MMCs exhibited a comparable, but somewhat greater uptake of fluorescent-labeled beads compared with MCs, suggesting an increased phagocytic ability. MCs and MMCs co-cultured with primary macrophages exhibited comparable significant decreases in LVS replication compared with macrophages cultured alone. Collectively, these results suggest that MMCs are phenotypically similar to MCs and appear equally effective in the control of intramacrophage F. tularensis LVS replication.

Mast cell TLR2 signaling is crucial for effective killing of Francisella tularensis

TLR signaling is critical for early host defense against pathogens, but the contributions of mast cell TLR-mediated mechanisms and subsequent effector functions during pulmonary infection are largely unknown. We have previously demonstrated that mast cells, through the production of IL-4, effectively control Francisella tularensis replication. In this study, the highly human virulent strain of F. tularensis SCHU S4 and the live vaccine strain were used to investigate the contribution of mast cell/TLR regulation of Francisella. Mast cells required TLR2 for effective bacterial killing, regulation of the hydrolytic enzyme cathepsin L, and for coordination and trafficking of MHC class II and lysosomal-associated membrane protein 2. Infected TLR2(-/-) mast cells, in contrast to wild-type and TLR4(-/-) cells, lacked detectable IL-4 and displayed increased cell death with a 2-3 log increase of F. tularensis replication, but could be rescued with rIL-4 treatment. Importantly, MHC class II and lysosomal-associated membrane protein 2 localization with labeled F. tularensis in the lungs was greater in wild-type than in TLR2(-/-) mice. These results provide evidence for the important effector contribution of mast cells and TLR2-mediated signaling on early innate processes in the lung following pulmonary F. tularensis infection and provide additional insight into possible mechanisms by which intracellular pathogens modulate respiratory immune defenses.

Immunization with dendritic cells pulsed ex vivo with recombinant chlamydial protease-like activity factor induces protective immunity against genital chlamydiamuridarum challenge

We have shown that immunization with soluble recombinant chlamydial protease-like activity factor (rCPAF) and a T helper 1 type adjuvant can induce significantly enhanced bacterial clearance and protection against Chlamydia-induced pathological sequelae in the genital tract. In this study, we investigated the use of bone marrow derived dendritic cells (BMDCs) pulsed ex vivo with rCPAF + CpG in an adoptive subcutaneous immunization for the ability to induce protective immunity against genital chlamydial infection. We found that BMDCs pulsed with rCPAF + CpG efficiently up-regulated the expression of activation markers CD86, CD80, CD40, and major histocompatibility complex class II (MHC II), and secreted interleukin-12, but not IL-10 and IL-4. Mice adoptively immunized with rCPAF + CpG-pulsed BMDCs or UV-EB + CpG-pulsed BMDCs produced elevated levels of antigen-specific IFN-γ and enhanced IgG1 and IgG2a antibodies. Moreover, mice immunized with rCPAF + CpG-pulsed BMDCs or UV-EB + CpG-pulsed BMDCs exhibited significantly reduced genital Chlamydia shedding, accelerated resolution of infection, and reduced oviduct pathology when compared to infected mock-immunized animals. These results suggest that adoptive subcutaneous immunization with ex vivo rCPAF-pulsed BMDCs is an effective approach, comparable to that induced by UV-EB–BMDCs, for inducing robust anti-Chlamydia immunity.

Non-FcεR bearing mast cells secrete sufficient interleukin-4 to control Francisella tularensis replication within macrophages

Mast cells have classically been implicated in the triggering of allergic and anaphylactic reactions. However, recent findings have elucidated the ability of these cells to selectively release a variety of cytokines leading to bacterial clearance through neutrophil and dendritic cell mobilization, and suggest an important role in innate host defenses. Our laboratory has established a primary bone marrow derived mast cell-macrophage co-culture system and found that mast cells mediated a significant inhibition of Francisella tularensis live vaccine strain (LVS) uptake and replication within macrophages through contact and the secreted product interleukin-4 (IL-4). In this study, we utilized P815 mast cells and J774 macrophages to further investigate whether mast cell activation by non-FcεR driven signals could produce IL-4 and control intramacrophage LVS replication. P815 supernatants collected upon activation by the mast cell activating peptide MP7, as well as P815 cells co-cultured with J774 macrophages, exhibited marked inhibition of bacterial uptake and replication, which correlated with the production of IL-4. The inhibition noted in vitro was titratable and preserved at ratios relevant to cellular infiltration events following pulmonary challenge. Collectively, our data suggest that both primary mast cell and P815 mast cell (lacking FcεR) secreted IL-4 can control intramacrophage Francisella replication.

The elucidation of the oral/respiratory axis in inducing protective immunity against Francisella tularensis (161.22)

Using a Francisella tularensis subspecies novicida live attenuated vaccine strain (U112ΔiglB), we have shown that oral vaccination of C57BL/6 mice induces significant protective immunity against pulmonary challenge with the highly human virulent F. tularensis strain SCHU S4. This protection is primarily mediated by antigen-specific CD4+ T cells and IFN-γ production and is dependent on mucosal IgA expression. We are examining the mechanism(s) by which the oral/respiratory axis induces optimal protective immunity against F. tularensis. Intestinal M-cells play an important role in oral vaccination by trafficking antigens from the lumen to the lamina propria and in presentation of antigens to underlying APCs for the subsequent induction of mucosal immunity. We have shown that mCherry-labeled U112ΔiglB co-localizes to intestinal mouse M-cells by 90 minutes following vaccination. Localization to M-cells was further verified with mouse ileal loops. Translocation of U112ΔiglB has also been demonstrated through M-cell-like-cells in an in vitro transwell co-culture system similar to M-cell trophic enteric bacteria. Current studies are examining the functional importance of intestinal M-cells in induction of mucosal immunity for the rational development of an effective oral vaccine against pulmonary tularemia. These studies will provide information for the general design of oral vaccines using live attenuated bacterial strains.

Intranasal vaccination with a defined live attenuated vaccine strain (ΔFTN0109) induces protective immunity against heterotypic pulmonary bacterial challenge. (106.29)

The need for an efficacious vaccine against the potential bioterrorism agent Francisella tularensis is a consequence of its low infectious dose, high mortality rate, and ability to be spread via aerosol, leading to pneumonic disease. FTN0109 is a novel protein that may be associated with the outer membrane of the bacterium and which is expressed across all subspecies of Francisella. In this study, we sought to determine the efficacy of ΔFTN0109 as a putative vaccine candidate. Using intramacrophage replication assays, ΔFTN0109 has been shown to be highly attenuated for growth. Moreover, the LD50 for this defined vaccine strain is &gt;105 CFU in BALB/c and C57BL/6 mice following intranasal challenge in comparison to its parental strain U112 (LD50&lt;10 CFU). Intranasal vaccination with ΔFTN0109 induces the expression of splenic antigen-specific IFN-γ and IL-2, with concurrent induction of preferential Th1 humoral responses (increased serum IgG2a over IgG1). Intranasal immunization with ΔFTN0109 confers complete protection in BALB/c mice against a subsequent pulmonary challenge with the heterotypic subspecies holarctica Live Vaccine Strain (LVS). Lungs, livers, and spleens of vaccinated and LVS-challenged mice exhibited significant reductions in bacterial burdens compared to mock-vaccinated and challenged animals. Current studies are ongoing to further clarify the mechanisms by which protection is conferred following vaccination with ΔFTN0109.

Evasion of IFN-γ signaling by Francisella novicida is dependent upon Francisella outer membrane protein C

Background

Francisella tularensis is a Gram-negative facultative intracellular bacterium and the causative agent of the lethal disease tularemia. An outer membrane protein (FTT0918) of F. tularensis subsp. tularensis has been identified as a virulence factor. We generated a F. novicida (F. tularensis subsp. novicida) FTN_0444 (homolog of FTT0918) fopC mutant to study the virulence-associated mechanism(s) of FTT0918.

Methods and Findings

The ΔfopC strain phenotype was characterized using immunological and biochemical assays. Attenuated virulence via the pulmonary route in wildtype C57BL/6 and BALB/c mice, as well as in knockout (KO) mice, including MHC I, MHC II, and µmT (B cell deficient), but not in IFN-γ or IFN-γR KO mice was observed. Primary bone marrow derived macrophages (BMDM) prepared from C57BL/6 mice treated with rIFN-γ exhibited greater inhibition of intracellular ΔfopC than wildtype U112 strain replication; whereas, IFN-γR KO macrophages showed no IFN-γ-dependent inhibition of ΔfopC replication. Moreover, phosphorylation of STAT1 was downregulated by the wildtype strain, but not the fopC mutant, in rIFN-γ treated macrophages. Addition of N^G-monomethyl-L-arginine, an NOS inhibitor, led to an increase of ΔfopC replication to that seen in the BMDM unstimulated with rIFN-γ. Enzymatic screening of ΔfopC revealed aberrant acid phosphatase activity and localization. Furthermore, a greater abundance of different proteins in the culture supernatants of ΔfopC than that in the wildtype U112 strain was observed.

Conclusions

F. novicida FopC protein facilitates evasion of IFN-γ-mediated immune defense(s) by down-regulation of STAT1 phosphorylation and nitric oxide production, thereby promoting virulence. Additionally, the FopC protein also may play a role in maintaining outer membrane stability (integrity) facilitating the activity and localization of acid phosphatases and other F. novicida cell components.

Mast cell/IL-4 control of Francisella tularensis replication and host cell death is associated with increased ATP production and phagosomal acidification

Mast cells are now recognized as effective modulators of innate immunity. We recently reported that mast cells and secreted interleukin-4 (IL-4) effectively control intramacrophage replication of Francisella tularensis Live Vaccine Strain (LVS), and that mice deficient in mast cells or IL-4 receptor (IL-4R(-/-)) exhibit greater susceptibility to pulmonary challenge. In this study, we further evaluated the mechanism(s) by which mast cells/IL-4 control intramacrophage bacterial replication and host cell death, and found that IL-4R(-/-) mice exhibited significantly greater induction of active caspase-3 within lung macrophages than wild-type animals following intranasal challenge with either LVS or the human virulent type A strain SCHU S4. Treatment of LVS-infected bone-marrow-derived macrophages with a pancaspase inhibitor (zVAD) did not alter bacterial replication, but minimized active caspase-3 and other markers (Annexin V and propidium iodide) of cell death, whereas treatment with both rIL-4 and zVAD resulted in concomitant reduction of both parameters, suggesting that inhibition of bacterial replication by IL-4 was independent of caspase activation. Interestingly, IL-4-treated infected macrophages exhibited significantly increased ATP production and phagolysosomal acidification, as well as enhanced mannose receptor upregulation and increased internalization with acidification, which correlated with observations in mast cell-macrophage co-cultures, with resultant decreases in F. tularensis replication.

Mannose-containing oligosaccharides of non-specific human secretory immunoglobulin A mediate inhibition of Vibrio cholerae biofilm formation

The role of antigen-specific secretory IgA (SIgA) has been studied extensively, whereas there is a limited body of evidence regarding the contribution of non-specific SIgA to innate immune defenses against invading pathogens. In this study, we evaluated the effects of non-specific SIgA against infection with Vibrio cholerae O139 strain MO10 and biofilm formation. Seven day old infant mice deficient in IgA (IgA^-/- mice) displayed significantly greater intestinal MO10 burden at 24 hr post-challenge when compared to IgA^+/+ pups. Importantly, cross-fostering of IgA^-/- pups with IgA^+/+ nursing dams reversed the greater susceptibility to MO10 infection, suggesting a role for non-specific SIgA in protection against the infection. Since biofilm formation is associated with virulence of MO10, we further examined the role of human non-specific SIgA on this virulence phenotype of the pathogen. Human non-specific SIgA, in a dose-dependent fashion, significantly reduced the biofilm formation by MO10 without affecting the viability of the bacterium. Such an inhibitory effect was not induced by human serum IgA, IgG, or IgM, suggesting a role for the oligosaccharide-rich secretory component (SC) of SIgA. This was supported by the demonstration that SIgA treated with endoglycosidase H, to cleave the high-mannose containing terminal chitobiose residues, did not induce a reduction in biofilm formation by MO10. Furthermore, the addition of free mannose per se, across a wide dose range, induced significant reduction in MO10 biofilm formation. Collectively, these results suggest that mannose containing oligosacchardies within human non-specific secretory IgA can alter important virulence phenotypes of Vibrio cholerae such as biofilm formation, without affecting viability of the microorganism. Such effects may contribute significantly to innate immune defenses against invading pathogens in vivo in the gastrointestinal tract.

Vaccination with the defined chlamydial secreted protein CPAF induces robust protection against female infertility following repeated genital chlamydial challenge

We previously have shown the efficacy of recombinant (r) chlamydial protease-like activity factor (CPAF) vaccination against hydrosalpinx development following primary genital chlamydial challenge. In this study, we evaluated further the protection induced by rCPAF vaccination against infertility. Following primary challenge, fertility levels were not significantly different between the mock- and CPAF-vaccinated and Chlamydia alone challenged mice. However, following secondary genital chlamydial challenge, mock (PBS) immunized mice displayed a significant reduction of fertility compared to age-matched naïve mice, while mice vaccinated intranasally with rCPAF+CpG displayed significant prevention of infertility. These results suggest that hydrosalpinx may be a reliable indicator of impending infertility, and that rCPAF is a promising candidate to prevent infertility resulting from repeated genital chlamydial infections.

The contribution of interleukin-12/interferon-gamma axis in protection against neonatal pulmonary Chlamydia muridarum challenge

Neonatal Chlamydia trachomatis pneumonia has been associated with respiratory sequelae in later life. We recently established a mouse model of neonatal pulmonary Chlamydia muridaum infection and found an important contribution of IFN-gamma to protective immunity. In this study, we further characterized the role of Th1-type cytokines; IL-12, IFN-gamma, and IFN-gamma signaling using mice genetically deficient in IL-12, IFN-gamma, or IFN-gamma receptor 1. All 3 knockout (KO) mice challenged intranasally with C. muridarum 1 day after birth exhibited 100% mortality by day 17 post-challenge whereas wild-type (WT) animals survived the monitoring period of 1 month. The KO mice exhibited greater lung bacterial burdens and enhanced dissemination to the liver, compared to WT animals. The inflammatory cellular infiltration in C. muridarum-challenged KO animals was significantly reduced in the lungs, but markedly enhanced in the livers of the KO mice compared to similarly challenged WT mice. It was also found that a deficiency in IL-12 or IFN-gamma resulted in correspondingly reduced IFN-gamma or IL-12 production, respectively, suggesting an intricate interdependence in the induction of these cytokines. Collectively, these results suggest that the IL-12/ IFN-gamma axis induces pulmonary cellular infiltration, induces bacterial clearance from the lung, reduces dissemination to other organs, and promotes the survival of the host during neonatal pulmonary chlamydial infection.

The Fischer 344 rat reflects human susceptibility to francisella pulmonary challenge and provides a new platform for virulence and protection studies

Background

The pathogenesis of Francisella tularensis, the causative agent of tularemia, has been primarily characterized in mice. However, the high degree of sensitivity of mice to bacterial challenge, especially with the human virulent strains of F. tularensis, limits this animal model for screening of defined attenuated vaccine candidates for protection studies.

Methods and Findings

We analyzed the susceptibility of the Fischer 344 rat to pulmonary (intratracheal) challenge with three different subspecies (subsp) of F. tularensis that reflect different levels of virulence in humans, and characterized the bacterial replication profile in rat bone marrow-derived macrophages (BMDM). In contrast to the mouse, Fischer 344 rats exhibit a broader range of sensitivity to pulmonary challenge with the human virulent subsp. tularensis and holarctica. Unlike mice, Fischer rats exhibited a high degree of resistance to pulmonary challenge with LVS (an attenuated derivative of subsp. holarctica) and subsp. novicida. Within BMDM, subsp. tularensis and LVS showed minimal replication, subsp. novicida showed marginal replication, and subsp. holartica replicated robustly. The limited intramacrophage replication of subsp. tularensis and novicida strains was correlated with the induction of nitric oxide production. Importantly, Fischer 344 rats that survived pulmonary infection with subsp. novicida were markedly protected against subsequent pulmonary challenge with subsp. tularensis, suggesting that subsp. novicida may be a useful platform for the development of vaccines against subsp. tularensis.

Conclusions

The Fischer 344 rat exhibits similar sensitivity to F. tularensis strains as that reported for humans, and thus the Fischer 344 ray may serve as a better animal model for tularemia vaccine development.

Heat denatured enzymatically inactive recombinant chlamydial protease-like activity factor induces robust protective immunity against genital chlamydial challenge

We have shown previously that vaccination with recombinant chlamydial protease-like activity factor (rCPAF) plus interleukin-12 as an adjuvant induces robust protective immunity against primary genital Chlamydia muridarum challenge in mice. Since CPAF is a protease, we compared the effects of enzymatically active and inactive (heat denatured) rCPAF to determine whether proteolytic activity is expendable for the induction of protective immunity against chlamydial challenge. Active, but not inactive, rCPAF immunization induced high levels of anti-active CPAF antibody, whereas both induced robust splenic CPAF-specific IFN-gamma production. Vaccination with active or inactive rCPAF induced enhanced vaginal chlamydial clearance as early as day 6 with complete resolution of infection by day 18, compared to day 30 in mock-vaccinated and challenged animals. Importantly, significant and comparable reductions in oviduct pathology were observed in active and inactive rCPAF-vaccinated mice compared to mock-vaccinated animals. Thus, rCPAF induced anti-chlamydial immunity is largely independent of enzymatic activity and secondary or higher order protein conformation.

Chlamydial protease-like activity factor--insights into immunity and vaccine development

Chlamydia trachomatis is a Gram-negative obligate intracellular pathogen that remains the leading cause of bacterial sexually transmitted disease worldwide, despite the availability of efficacious antimicrobial therapy. Given that chlamydial infections cause severe pathological sequelae in the upper genital tract, a licensed vaccine to prevent infection and disease would be an ideal solution. Chlamydial protease-like activity factor (CPAF) is a protein secreted in considerable amounts into the cytosol of infected cells and released into the extracellular milieu upon cellular lysis, which therefore is accessible to the host immune system. This is further substantiated by the observation that CPAF is immunodominant among other antigens in Chlamydia sero-positive humans. The efficacy of vaccination with CPAF against genital chlamydial challenge has been evaluated extensively in the murine model. This review will discuss important insights into the potential of CPAF as a component of an anti-chlamydial vaccine.

Proteolytic bacteria in the lower digestive tract of poultry may affect avian influenza virus pathogenicity

Proteolytic cleavage of hemagglutinin is required for cell entry by receptor-mediated endocytosis and plays a key role in pathogenicity of the influenza virus. Despite several studies describing relationships between bacterial proteases and influenza A viral activation in mammals, very little is known about the role of the normal bacterial flora of birds on hemagglutinin activation. We examined the indigenous intestinal microflora of 100 mixed-sex, 27-d-old Ross chickens from a commercial poultry facility for protease-secreting bacteria. Protease-secreting bacteria were isolated from 82 of 100 chickens with 50 birds exhibiting 2 or more protease-secreting bacterial species. A total of 20 protease-secreting bacterial species were identified: 17 gram-positive cocci, 2 gram-positive rods, and 1 gram-negative rod. Enterococcus faecalis, Enterococcus gallinarum, and Proteus mirabilis were the most frequently observed protease-secreting bacterial species. The presence of proteolytic bacteria in the intestinal tract of poultry in this study suggests the possibility of yet-to-be-described role(s) in cleavage of hemagglutinin that may alter the pathogenicity of avian influenza viruses.

A limited role for antibody in protective immunity induced by rCPAF and CpG vaccination against primary genital Chlamydia muridarum challenge

Mice deficient in B cells (micromT mice) were used to evaluate the role of antibody in enhanced chlamydial clearance and reduction of pathology afforded by vaccination with recombinant chlamydial protease-like activity factor (rCPAF). Enhanced, but comparable, chlamydial clearance was observed in micromT and wild-type (WT) mice after rCPAF+CpG vaccination. Chlamydia-induced pathology was present in mock-immunized animals, but at significantly greater levels in micromT than WT mice, whereas vaccinated micromT and WT mice exhibited similar reductions in pathology. Thus, antibodies may play a role in protection against chlamydial pathology after primary infection, but were largely dispensable in rCPAF+CpG-induced chlamydial clearance and reduction in pathology.

Mast cells induce alternative activation and inhibit caspase-3 mediated apoptosis of Francisella tularensis infected macrophages (44.24)

Francisella tularensis is a highly infectious Gram-negative bacterial pathogen and the causative agent of pneumonic tularemia. We recently demonstrated inhibition of F. tularensis LVS replication in macrophages via mast cell production of interleukin-4 (IL-4). We have further analyzed the interactions of mast cells and macrophages using a primary bone marrow derived mast cell-macrophage co-culture system and determined that mast cells inhibit F. tularensis-induced macrophage apoptosis. Specifically, mast cells co-cultured with macrophages significantly reduced intramacrophage LVS growth and expression of apoptotic proteins caspase-3 (19.9%) and PARP (Poly-ADP ribose polymerase, 16.0%) compared to macrophages cultured alone (48.2% and 56.4%, respectively). The inhibition of LVS-induced apoptosis within infected macrophages also was seen by the direct addition of recombinant IL-4 and corresponded with up-regulation of mannose receptor expression and arginase activity which are associated with the alternative activation of macrophages. Moreover, IL4R-/- mice were more susceptible to intranasal challenge and exhibited greater caspase-3 activity in lung macrophages (12.9%) compared to similarly challenged wild-type (4.7%) animals. These results support a role for mast cells and IL-4 in control of bacterial replication and apoptosis following pulmonary LVS infection.

National Institutes of Health grant PO1 AI057986; NIH/NIGMS MBRS-RISE GM60655

Antigen-specific CD4+ T cells produce sufficient IFN-gamma to mediate robust protective immunity against genital Chlamydia muridarum infection

Chlamydia has been shown to evade host-specific IFN-gamma-mediated bacterial killing; however, IFN-gamma-deficient mice exhibit suboptimal late phase vaginal Chlamydia muridarum clearance, greater dissemination, and oviduct pathology. These findings introduce constraints in understanding results from murine chlamydial vaccination studies in context of potential implications to humans. In this study, we used mice deficient in either IFN-gamma or the IFN-gamma receptor for intranasal vaccination with a defined secreted chlamydial Ag, chlamydial protease-like activity factor (CPAF), plus CpG and examined the role of IFN-gamma derived from adoptively transferred Ag-specific CD4+ T cells in protective immunity against genital C. muridarum infection. We found that early Ag-specific IFN-gamma induction and CD4+ T cell infiltration correlates with the onset of genital chlamydial clearance. Adoptively transferred IFN-gamma competent CPAF-specific CD4+ T cells failed to enhance the resolution of genital chlamydial infection within recipient IFN-gamma receptor-deficient mice. Conversely, IFN-gamma production from adoptively transferred CPAF-specific CD4+ T cells was sufficient in IFN-gamma-deficient mice to induce early resolution of infection and reduction of subsequent pathology. These results provide the first direct evidence that enhanced anti-C. muridarum protective immunity induced by Ag-specific CD4+ T cells is dependent upon IFN-gamma signaling and that such cells produce sufficient IFN-gamma to mediate the protective effects. Additionally, MHC class II pathway was sufficient for induction of robust protective anti-C. muridarum immunity. Thus, targeting soluble candidate Ags via MHC class II to CD4+ T cells may be a viable vaccine strategy to induce optimal IFN-gamma production for effective protective immunity against human genital chlamydial infection.

Endogenous IFN-gamma production is induced and required for protective immunity against pulmonary chlamydial infection in neonatal mice

Chlamydia trachomatis infection in neonates, not adults, has been associated with the development of chronic respiratory sequelae. Adult chlamydial infections induce Th1-type responses that subsequently clear the infection, whereas the neonatal immune milieu in general has been reported to be biased toward Th2-type responses. We examined the protective immune responses against intranasal Chlamydia muridarum challenge in 1-day-old C57BL/6 and BALB/c mice. Infected C57BL/6 pups displayed earlier chlamydial clearance (day 14) compared with BALB/c pups (day 21). However, challenged C57BL/6 pups exhibited prolonged deficits in body weight gain (days 12-30) compared with BALB/c pups (days 9-12), which correlated with continual pulmonary cellular infiltration. Both strains exhibited a robust Th1-type response, including elevated titers of serum antichlamydial IgG2a and IgG2b, not IgG1, and elevated levels of splenic C. muridarum-specific IFN-gamma, not IL-4, production. Additionally, elevated IFN-gamma, not IL-4 expression, was observed locally in the infected lungs of both mouse strains. The immune responses in C57BL/6 pups were significantly greater compared with BALB/c pups after chlamydial challenge. Importantly, infected mice deficient in IFN-gamma or IFN-gamma receptor demonstrated enhanced chlamydial dissemination, and 100% of animals died by 2 wk postchallenge. Collectively, these results indicate that neonatal pulmonary chlamydial infection induces a robust Th1-type response, with elevated pulmonary IFN-gamma production, and that endogenous IFN-gamma is important in protection against this infection. The enhanced IFN-gamma induction in the immature neonatal lung also may be relevant to the development of respiratory sequelae in adult life.

Intranasal immunization with chlamydial protease-like activity factor and CpG deoxynucleotides enhances protective immunity against genital Chlamydia muridarum infection

We have reported recently that intranasal (i.n.) vaccination with chlamydial protease-like activity factor (CPAF) and interleukin-12 (IL-12) enhances protective immunity against genital chlamydial challenge. In this study, we show that i.n. or intraperitoneal (i.p.) vaccination with CPAF plus CpG deoxynucleotides (CpG), an alternative T helper 1 (Th1) adjuvant, induced robust CPAF-specific IFN-gamma responses and elevated levels of serum antibody and vaginal IgA production. CPAF+CpG vaccinated animals displayed accelerated genital chlamydial clearance, and minimal hydrosalpinx and inflammatory cellular infiltration compared to mock-immunized (PBS) challenged animals. Together, CpG dexoynucleotides are an efficacious alternative Th1 adjuvant with CPAF to induce protective anti-chlamydial immunity.

The protective efficacy of chlamydial protease-like activity factor vaccination is dependent upon CD4+ T cells

We have previously determined the protective efficacy of intranasal vaccination with chlamydial protease-like activity factor (CPAF) against genital chlamydial infection. Since T-helper 1 (Th1) responses are important for anti-chlamydial immunity, we examined the contribution of CD4(+) T cells in CPAF mediated immunity against intravaginal (i.vag.) Chlamydia muridarum infection in C57BL/6 mice. CPAF+IL-12 vaccination induced antigen-specific CD4(+) T cells that secreted elevated levels of IFN-gamma, and generated strong humoral responses. The protective effects of CPAF vaccination against genital chlamydial challenge were abrogated by anti-CD4 neutralizing antibody treatment. Moreover, anti-chlamydial immunity could be adoptively transferred to naïve recipients using CPAF-specific CD4(+) T cells. Therefore, CPAF mediated anti-chlamydial immunity is highly dependent upon antigen-specific CD4(+) T cells.

Chlamydial protease-like activity factor induces protective immunity against genital chlamydial infection in transgenic mice that express the human HLA-DR4 allele

There is no licensed vaccine available against Chlamydia trachomatis, the leading cause of bacterial sexually transmitted disease. We have found that intranasal immunization with recombinant chlamydial protease-like activity factor (CPAF) induces CD4(+) T-cell- and gamma interferon (IFN-gamma)-dependent protective immunity against murine genital chlamydial infection, thus making CPAF a viable vaccine candidate for further characterization. HLA-DR4 is the predominant allele involved in chlamydial antigen presentation to CD4(+) T cells in humans. We used engineered mice that lack endogenous major histocompatibility complex class II (MHC-II) alleles but express a human HLA allele (HLA-DR4 transgenic [tg] mice) to examine primary immune and CPAF-mediated responses against genital Chlamydia muridarum challenge. Upon primary bacterial exposure, HLA-DR4 tg mice developed Chlamydia-specific IFN-gamma and antibody production and resolved the infection within 30 days, similar to challenged conventional C57BL/6 animals. Moreover, C. muridarum-challenged HLA-DR4 tg mice exhibited CPAF-specific antibody and IFN-gamma production. Upon CPAF-plus-interleukin-12 (IL-12) vaccination, HLA-DR4 tg animals exhibited robust CPAF-specific IFN-gamma production and elevated titers of anti-CPAF total antibody and immunoglobulin G2a (IgG2a) and lower titers of IgG2b and IgG1 antibodies. HLA-DR4 tg and C57BL/6 mice vaccinated with CPAF plus IL-12 resolved the primary genital chlamydial infection significantly earlier than mock-immunized animals, whereas similarly vaccinated MHC class II-deficient mice displayed minimal antigen-specific immune responses and failed to resolve the infection even at 30 days postchallenge. Together, these results demonstrate the importance of human HLA-DR4 molecules in the recognition and presentation of CPAF epitopes, leading to the generation of protective antichlamydial immunity and making these mice a valuable model for mapping HLA-DR4-restricted chlamydial epitopes.