A predominant role for antibody in acquired immunity to chlamydial genital tract reinfection

Immunohistochemical characterization of the immune cell response during chlamydial infection in the male and female koala (Phascolarctos cinereus) reproductive tract

Chlamydiosis is one of the main causes of the progressive decline of koala populations in eastern Australia. While histologic, immunologic, and molecular studies have provided insights into the basic function of the koala immune system, the in situ immune cell signatures during chlamydial infection of the reproductive tract in koalas have not been investigated. Thirty-two female koalas and 47 males presented to wildlife hospitals with clinical signs suggestive of Chlamydia infection were euthanized with the entire reproductive tract collected for histology; immunohistochemistry (IHC) for T-cell (CD3ε, CD4, and CD8α), B-cell (CD79b), and human leukocyte antigen (HLA)-DR markers; and quantitative real-time polymerase chain reaction (rtPCR) for Chlamydia pecorum. T-cells, B-cells, and HLA-DR-positive cells were observed in both the lower and upper reproductive tracts of male and female koalas with a statistically significant associations between the degree of the inflammatory reaction; the number of CD3, CD4, CD79b, and HLA-DR positive cells; and the PCR load. CD4-positive cells were negatively associated with the severity of the gross lesions. The distribution of immune cells was also variable according to the location within the genital tract in both male and female koalas. These preliminary results represent a step forward towards further exploring mechanisms behind chlamydial infection immunopathogenesis, thus providing valuable information about the immune response and infectious diseases in free-ranging koalas.

Safety and efficacy of C. muridarum vaccines adjuvanted with CpG-1826 and four concentrations of Montanide-ISA-720-VG

It is recommended that the adjuvant Montanide ISA 720 VG be used at a concentration of 70% v/v. At this concentration, Montanide causes at the site of immunization a local granuloma that can last for several weeks. To determine the safety and protective efficacy of a Chlamydia muridarum MOMP vaccine, formulated with CpG-1826 and four different concentrations of Montanide (70%, 50%, 30% and 10%), BALB/c (H-2d) female mice were immunized twice intramuscularly. Local reactogenicity was significant for vaccines formulated with 70% or 50% Montanide but not for those inoculated with 30% or 10% Montanide. Robust humoral and cell mediated memory immune responses were elicited by the 70%, 50% and 30% Montanide formulations. Mice were challenged intranasally with 104 C. muridarum inclusion forming units (IFU). Based on changes in body weight, lungs's weight and number of IFU recovered, mice vaccinated with the 70%, 50% and 30% Montanide formulations were significantly protected, but not mice receiving 10% Montanide. To conclude, we recommend the 30% Montanide concentration to be tested in humans and animal models to determine its safety and efficacy, in comparison to the 70% Montanide concentration currently used. The 30% Montanide formulation could significantly facilitate licensing of this adjuvant for human use.

Antibodies from chlamydia-infected individuals facilitate phagocytosis via Fc receptors

Non-neutralizing functions of antibodies, including phagocytosis, may play a role in Chlamydia trachomatis (CT) infection, but these functions have not been studied and assays are lacking. We utilized a flow-cytometry-based assay to determine whether serum samples from a well-characterized cohort of CT-infected and naïve control individuals enhanced phagocytosis via Fc-receptor-expressing THP-1 cells, and whether this activity correlated with antibody titers. Fc-receptor-mediated phagocytosis was detected only in CT+ donors. Phagocytosis generally did not correlate well with antibody titer. In addition, we found that complement from both CT+ and negative individuals enhanced phagocytosis of CT into primary neutrophils. These results suggest that anti-CT antibodies can have functions that are not reflected by titer. This method could be used to quantitively measure Fc-receptor-mediated function of anti-CT antibodies or complement activity and could reveal new immune correlates of protection.

In silico design and analysis of a multiepitope vaccine against Chlamydia

Chlamydia trachomatis (Ct) is the most common sexually transmitted bacterial infection worldwide, potentially leading to severe pathologies including pelvic inflammatory disease, ectopic pregnancy, and tubal infertility if left untreated. Current strategies, including screening and antibiotics, have limited effectiveness due to high rates of asymptomatic cases and logistical challenges. A multiepitope prophylactic vaccine could afford long-term protection against infection. Immunoinformatic analyses were employed to design a multiepitope Chlamydia vaccine antigen. B- and T-cell epitopes from five highly conserved and immunogenic Ct antigens were predicted and selected for the vaccine design. The final construct, adjuvanted with cholera toxin A1 subunit (CTA1), was further screened for immunogenicity. CTA1-MECA (multiepitope Chlamydia trachomatis antigen) was identified as antigenic and nonallergenic. A tertiary structure was predicted, refined, and validated as a good quality model. Molecular docking exhibited strong interactions between the vaccine and toll-like receptor 4 (TLR4). Additionally, immune responses consistent with protection including IFN-γ, IgG + IgM antibodies, and T- and B-cell responses were predicted following vaccination in an immune simulation. Expression of the construct in an Escherichia coli expression vector proved efficient. To further validate the vaccine efficacy, we assessed its immunogenicity in mice. Immunization with CTA1-MECA elicited high levels of Chlamydia-specific antibodies in mucosal and systemic compartments.

Antibody responses to Chlamydia trachomatis vaccine candidate antigens in Chlamydia-infected women and correlation with antibody-mediated phagocytosis of elementary bodies

Murine research has revealed a significant role for antibody responses in protection against Chlamydia reinfection. To explore potential humoral immune markers of protection elicited by Chlamydia trachomatis (CT) antigens in humans in the context of presumed clinical correlates of protection, we used both an IgG1-based ELISA and a conventional total IgG ELISA to evaluate antibody responses. We evaluated responses to five CT outer membrane proteins (PmpE, PmpF, PmpG, PmpH, and MOMP), along with other promising CT antigens (Pgp3 and HSP60), negative control antigens (RecO and AtpE), and CT elementary bodies (EBs) in sera from a well-characterized cohort of 60 women with different CT infection outcomes, including two outcomes that are likely clinical correlates of protective immunity: spontaneous resolution of infection and absence of reinfection after treatment. Furthermore, we used a flow cytometry-based assay to measure antibody-mediated phagocytosis by neutrophils in these sera. Results demonstrated that IgG1 ELISA displayed higher sensitivity than conventional total IgG ELISA in assessing antibody responses to CT EBs and antigens. Pgp3 IgG1 ELISA exhibited the highest sensitivity compared to IgG1 ELISA incorporating CT EBs or other antigens, confirming Pgp3 IgG1 ELISA as an ideal assay for CT antibody detection. Most (95%) sera from women with CT infection outcomes exhibited antibody-mediated phagocytosis of CT EBs, which was significantly correlated with IgG1 antibody responses to MOMP, Pgp3, HSP60, and PmpF. However, neither IgG1 responses to CT antigens and EBs nor antibody-mediated phagocytosis were associated with clinical correlates of protection. These findings suggest that neither CT IgG1 antibody detection nor antibody-mediated phagocytosis will be useful as immune correlates of protection against CT infection in humans.

Evaluation of three formulations based on Polymorphic membrane protein D in mice infected with Chlamydia trachomatis

The significant impact of Chlamydia trachomatis(Ct) infections worldwide highlights the need to develop a prophylactic vaccine that elicits effective immunity and protects the host from the immunopathological effects of Ct infection. The aim of this study was to evaluate a vaccine based on a fragment of the Polymorphic membrane protein D (FPmpD) of C. trachomatis as an immunogen using a heterologous DNA prime-protein boost strategy in female mice Three different formulations were evaluated as protein boost: free recombinant FPmpD (rFPmpD) or rFPmpD formulated with a liposomal adjuvant alternatively supplemented with CpG or a cationic gemini lipopeptide as immunostimulants. The three candidates induced an increase in the cervicovaginal and systemic titers of anti-rFPmpD antibodies in two strains of mice (BALB/c and C57BL/6), with no evidence of fertility alterations. The three formulations induced a rapid and robust humoral immune response upon the Ct challenge. However, the booster with free rFPmpD more efficiently reduced the shedding of infective Ct and prevented the development of immunopathology. The formulations containing adjuvant induced a strong inflammatory reaction in the uterine tissue. Hence, the prime-boost strategy with the adjuvant-free FPmpD vaccine formulation might constitute a promissory candidate to prevent C. trachomatis intravaginal infection.

Plasmid-mediated virulence in Chlamydia

Chlamydia trachomatis infection of ocular conjunctiva can lead to blindness, while infection of the female genital tract can lead to chronic pelvic pain, ectopic pregnancy, and/or infertility. Conjunctival and fallopian tube inflammation and the resulting disease sequelae are attributed to immune responses induced by chlamydial infection at these mucosal sites. The conserved chlamydial plasmid has been implicated in enhancing infection, via improved host cell entry and exit, and accelerating innate inflammatory responses that lead to tissue damage. The chlamydial plasmid encodes eight open reading frames, three of which have been associated with virulence: a secreted protein, Pgp3, and putative transcriptional regulators, Pgp4 and Pgp5. Although Pgp3 is an important plasmid-encoded virulence factor, recent studies suggest that chlamydial plasmid-mediated virulence extends beyond the expression of Pgp3. In this review, we discuss studies of genital, ocular, and gastrointestinal infection with C. trachomatis or C. muridarum that shed light on the role of the plasmid in disease development, and the potential for tissue and species-specific differences in plasmid-mediated pathogenesis. We also review evidence that plasmid-associated inflammation can be independent of bacterial burden. The functions of each of the plasmid-encoded proteins and potential molecular mechanisms for their role(s) in chlamydial virulence are discussed. Although the understanding of plasmid-associated virulence has expanded within the last decade, many questions related to how and to what extent the plasmid influences chlamydial infectivity and inflammation remain unknown, particularly with respect to human infections. Elucidating the answers to these questions could improve our understanding of how chlamydia augment infection and inflammation to cause disease.

Evaluation of Four Adjuvant Combinations, IVAX-1, IVAX-2, CpG-1826+Montanide ISA 720 VG and CpG-1018+Montanide ISA 720 VG, for Safety and for Their Ability to Elicit Protective Immune Responses in Mice against a Respiratory Challenge with Chlamydia muridarum

There is an urgent need to produce a vaccine for Chlamydia trachomatis infections. Here, using the Chlamydia muridarum major outer membrane protein (MOMP) as an antigen, four adjuvant combinations IVAX-1 (MPLA+CpG-1018+AddaVax), IVAX-2 (MPLA+CpG-1018+AS03), CpG-1826+Montanide ISA 720 VG (CpG-1826+Mont) and CpG-1018+Montanide ISA 720 VG (CpG-1018+Mont), were tested for their local reactogenicity and ability to elicit protection in BALB/c mice against a respiratory challenge with C. muridarum. Immunization with IVAX-1 or IVAX-2 induced no significant local reactogenicity following intramuscular immunization. In contrast, vaccines containing Montanide resulted in the formation of a local granuloma. Based on the IgG2a/IgG1 ratio in serum, the four adjuvant combinations elicited Th1-biased responses. IVAX-1 induced the highest in vitro neutralization titers while CpG-1018+Mont stimulated the lowest. As determined by the levels of IFN-γ produced by T-cells, the most robust cellular immune responses were elicited in mice immunized with CpG-1018+Mont, while the weakest responses were mounted by mice receiving IVAX-1. Following the respiratory challenge, mice immunized with CpG-1018+Mont lost the least amount of body weight and had the lowest number of C. muridarum inclusion-forming units (IFUs) in the lungs, while those receiving IVAX-2 had lost the most weight and had the highest number of IFUs in their lungs. Animals vaccinated with CpG-1826+Mont had the lightest lungs while those immunized using IVAX-2 had the heaviest. To conclude, due to their safety and adjuvanticity, IVAX formulations should be considered for inclusion in human vaccines against Chlamydia.

IFNγ and Antibody Synergize To Enhance Protective Immunity against Chlamydia Dissemination and Female Reproductive Tract Reinfections

CD4 T cell-dependent IFNγ production and antibody are the two best known effectors for protective immunity against Chlamydia female reproductive tract (FRT) infection. Nevertheless, mice lacking either IFNγ or B cells can clear the vast majority of Chlamydia from the FRT, while suffering from varying degrees of disseminated infection. In this study, we investigated whether IFNγ and B cells play complementary roles in host defense against Chlamydia and evaluated their relative contributions in systemic and mucosal tissues. Using mice deficient in both IFNγ and B cells (IFNγ^-/- x μMT), we showed that mice lacking both effectors were highly susceptible to lethal systemic bacterial dissemination following Chlamydia muridarum intravaginal infection. Passive transfer of immune convalescent serum, but not recombinant IFNγ, reduced bacterial burden in both systemic and mucosal tissues in IFNγ^-/- x μMT mice. Notably, over the course of primary infection, we observed a reduction of bacterial shedding of more than 2 orders of magnitude in IFNγ^-/- x μMT mice following both C. muridarum and C. trachomatis FRT infections. In contrast, no protective immunity against C. muridarum reinfection was detected in the absence of IFNγ and B cells. Together, our results suggest that IFNγ and B cells synergize to combat systemic Chlamydia dissemination, while additional IFNγ and B cell-independent mechanisms exist for host resistance to Chlamydia in the lower FRT.

Heterologous prime-boost vaccination based on Polymorphic protein D protects against intravaginal Chlamydia trachomatis infection in mice

The control of the worldwide spread of sexually transmitted Chlamydia trachomatis (Ct) infection urgently demands the development of a preventive vaccine. In this work, we designed a vaccine based on a fragment of polymorphic protein D (FPmpD) that proved to be immunogenic enough to generate a robust systemic and mucosal IgG humoral immune response in two strains of mice. We used a heterologous prime-boost strategy, including simultaneous systemic and mucosal administration routes. The high titers of anti-PmpD antibodies elicited by this immunization scheme did not affect murine fertility. We tested the vaccine in a mouse model of Ct intravaginal infection. Anti-PmpD antibodies displayed potent neutralizing activity in vitro and protective effects in uterine tissues in vivo. Notably, the humoral immune response of PmpD-vaccinated mice was faster and stronger than the primary immune response of non-vaccinated mice when exposed to Ct. FPmpD-based vaccine effectively reduced Ct shedding into cervicovaginal fluids, bacterial burden at the genitourinary tract, and overall infectivity. Hence, the FPmpD-based vaccine might constitute an efficient tool to protect against Ct intravaginal infection and decrease the infection spreading.

The Role of IL-17 During Infections in the Female Reproductive Tract

Interleukin-17 (IL-17A) is a cytokine involved in a complex array of both protective and detrimental processes. Although early biological studies focused on the pro-inflammatory function of IL-17 in the context of autoimmune and inflammatory disorders, it has become increasingly evident that the roles of IL-17 are far more nuanced. Recent work has demonstrated that the functions of IL-17 are highly context- and tissue-dependent, and there is a fine balance between the pathogenic and protective functions of IL-17. This is especially evident in mucosal tissues such as the female reproductive tract, where IL-17 has been shown to play an important role in the immune response generated during fungal, bacterial and viral infections associated with protection, but also with inflammation. In this review, we discuss the evolving landscape of IL-17 biology within the context of the vaginal mucosa, focusing on key findings that highlight the importance of this cytokine in genital mucosal immunity.

Immunogenicity and Protective Capacity of a Virus-like Particle Vaccine against Chlamydia trachomatis Type 3 Secretion System Tip Protein, CT584

An effective vaccine against Chlamydia trachomatis is urgently needed as infection rates continue to rise and C. trachomatis causes reproductive morbidity. An obligate intracellular pathogen, C. trachomatis employs a type 3 secretion system (T3SS) for host cell entry. The tip of the injectosome is composed of the protein CT584, which represents a potential target for neutralization with vaccine-induced antibody. Here, we investigate the immunogenicity and efficacy of a vaccine made of CT584 epitopes coupled to a bacteriophage virus-like particle (VLP), a novel platform for Chlamydia vaccines modeled on the success of HPV vaccines. Female mice were immunized intramuscularly, challenged transcervically with C. trachomatis, and assessed for systemic and local antibody responses and bacterial burden in the upper genital tract. Immunization resulted in a 3-log increase in epitope-specific IgG in serum and uterine homogenates and in the detection of epitope-specific IgG in uterine lavage at low levels. By contrast, sera from women infected with C. trachomatis and virgin controls had similarly low titers to CT584 epitopes, suggesting these epitopes are not systemically immunogenic during natural infection but can be rendered immunogenic by the VLP platform. C. trachomatis burden in the upper genital tract of mice varied after active immunization, yet passive protection was achieved when immune sera were pre-incubated with C. trachomatis prior to inoculation into the genital tract. These data demonstrate the potential for antibody against the T3SS to contribute to protection against C. trachomatis and the value of VLPs as a novel platform for C. trachomatis vaccines.

Human genital antibody-mediated inhibition of Chlamydia trachomatis infection and evidence for ompA genotype-specific neutralization

The endocervix, the primary site of Chlamydia trachomatis (Ct) infection in women, has a unique repertoire of locally synthesized IgG and secretory IgA (SIgA) with contributions from serum IgG. Here, we assessed the ability of genital and serum-derived IgG and IgA from women with a recent positive Ct test to neutralize Ct elementary bodies (EBs) and inhibit inclusion formation in vitro in human endocervical epithelial cells. We also determined if neutralization was influenced by the major outer membrane protein (MOMP) of the infecting strain, as indicated by ompA gene sequencing and genotyping. At equivalent low concentrations of Ct EB (D/UW-3/Cx + E/UW-5/Cx)-specific antibody, genital-derived IgG and IgA and serum IgA, but not serum IgG, significantly inhibited inclusion formation, with genital IgA being most effective, followed by genital IgG, then serum IgA. The well-characterized Ct genotype D strain, D/UW-3/Cx, was neutralized by serum-derived IgG from patients infected with genotype D strains, genital IgG from patients infected with genotype D or E strains, and by genital IgA from patients infected with genotype D, E, or F strains. Additionally, inhibition of D/UW-3/Cx infection by whole serum, rather than purified immunoglobulin, was associated with levels of serum EB-specific IgG rather than the genotype of infecting strain. In contrast, a Ct genotype Ia clinical isolate, Ia/LSU-56/Cx, was neutralized by whole serum in a genotype and genogroup-specific manner, and inhibition also correlated with EB-specific IgG concentrations in serum. Taken together, these data suggest that (i) genital IgA most effectively inhibits Ct infection in vitro, (ii) human antibody-mediated inhibition of Ct infection is significantly influenced by the ompA genotype of the infecting strain, (iii) the genital antibody repertoire develops or matures differently compared to systemic antibody, and (iv) ompA genotype-specificity of inhibition of infection by whole serum can be overcome by high concentrations of Ct-specific IgG.

Chlamydia trachomatis Cross-Serovar Protection during Experimental Lung Reinfection in Mice

Chlamydia trachomatis causes most bacterial sexually transmitted diseases worldwide. Different major outer membrane proteins (MOMPs) define various serovars of this intracellular pathogen: In women, D to L3 can cause urethritis, cervicitis, salpingitis, and oophoritis, and, thus, infertility. Protective immunity might be serovar-specific since chlamydial infection does not appear to induce an effective acquired immunity and reinfections occur. A better understanding of induced cross-serovar protection is essential for the selection of suitable antigens in vaccine development. In our mouse lung infection screening model, we evaluated the urogenital serovars D, E, and L2 in this regard. Seven weeks after primary infection or mock-infection, respectively, mice were infected a second time with the identical or one of the other serovars. Body weight and clinical score were monitored for 7 days. Near the peak of the second lung infection, bacterial load, myeloperoxidase, IFN-γ, and TNF-α in lung homogenate, as well as chlamydia-specific IgG levels in blood were determined. Surprisingly, compared with mice that were infected then for the first time, almost independent of the serovar combination used, all acquired parameters of disease were similarly diminished. Our reinfection study suggests that efficient cross-serovar protection could be achieved by a vaccine combining chlamydial antigens that do not include nonconserved MOMP regions.

Induction of Protection in Mice against a Chlamydia muridarum Respiratory Challenge by a Vaccine Formulated with the Major Outer Membrane Protein in Nanolipoprotein Particles

Chlamydia trachomatis is a sexually transmitted bacterium that infects over 130 million individuals worldwide annually. To implement a vaccine, we developed a cell-free co-translational system to express the Chlamydia muridarum major outer membrane protein (MOMP). This approach uses a nanolipoprotein particles (tNLP) made from ApoA1 protein, amphiphilic telodendrimer and lipids that self-assemble to form 10-25 nm discs. These tNLP provide a protein-encapsulated lipid support to solubilize and fold membrane proteins. The cell-free system co-translated MOMP and ApoA1 in the presence of telodendrimer mixed with lipids. The MOMP-tNLP complex was amenable to CpG and FSL-1 adjuvant addition. To investigate the ability of MOMP-tNLP+CpG+FSL-1 to induce protection against an intranasal (i.n.) C. muridarum challenge, female mice were vaccinated intramuscularly (i.m.) or i.n. and i.m. simultaneously 4 weeks apart. Following vaccination with MOMP-tNLP+CpG+FSL-1, mice mounted significant humoral and cell-mediated immune responses. Following the i.n. challenge, mice vaccinated with MOMP-tNLP+CpG+FSL-1 i.n. + i.m. group were protected as determined by the percentage change in body weight and by the number of C. muridarum inclusion forming units (IFU) recovered from the lungs. To our knowledge, this is the first time a MOMP-based vaccine formulated in tNLP has been shown to protect against C. muridarum.

Cellular Basis for the Enhanced Efficacy of the Fms-Like Tyrosine Kinase 3 Ligand (FL) Adjuvanted VCG-Based Chlamydia abortus Vaccine

Efficacious vaccines are needed to control genital chlamydial diseases in humans and the veterinary industry. We previously reported a C. abortus (Cab) vaccine comprising recombinant Vibrio cholerae ghosts (rVCG) expressing the conserved and immunogenic N-terminal region of the Cab polymorphic membrane protein D (rVCG-Pmp18.1) protein that protected mice against intravaginal challenge. In this study, we investigated the immunomodulatory effect of the hematopoietic progenitor activator cytokine, Fms-like tyrosine kinase 3-ligand (FL) when co-administered with the rVCG-Pmp18.1 vaccine as a strategy to enhance the protective efficacy and the potential mechanism of immunomodulation. Groups of female C57BL/6J mice were immunized and boosted twice intranasally (IN) with rVCG-PmpD18.1 with and without FL or purified rPmp18.1 or rVCG-gD2 (antigen control) or PBS (medium) per mouse. The results revealed that co-administration of the vaccine with FL enhanced antigen-specific cellular and humoral immune responses and protected against live Cab genital infection. Comparative analysis of immune cell phenotypes infiltrating mucosal and systemic immune inductive tissue sites following immunization revealed that co-administration of rVCG-Pmp18.1 with FL significantly enhanced the number of macrophages, dendritic and NK cells, γδ and NK T cells in the spleen (systemic) and iliac lymph nodes (ILN) draining the genital tract (mucosal) tissues compared to rVCG-Pmp18.1 alone. Furthermore, FL enhanced monocyte infiltration in the ILN, while CD19+ B cells and CD4+ T cells were enhanced in the spleen. These results indicate that the immunomodulatory effect of FL is associated with its ability to mobilize innate immune cells and subsequent activation of robust antigen-specific immune effectors in mucosal and systemic lymphoid tissues.

Intranasal immunization with inactivated chlamydial elementary bodies formulated in VCG-chitosan nanoparticles induces robust immunity against intranasal Chlamydia psittaci challenge

Vaccines based on live attenuated Chlamydia elementary bodies (EBs) can cause disease in vaccinated animals and the comparably safer inactivated whole EBs are only marginally protective. Recent studies show that a vaccine formulation comprising UV-inactivated EBs (EB) and appropriate mucosal delivery systems and/or adjuvants induced significant protective immunity. We tested the hypothesis that intranasal delivery of UV-inactivated C. psittaci EB formulated in Vibrio cholerae ghosts (VCG)-chitosan nanoparticles will induce protective immunity against intranasal challenge in SPF chickens. We first compared the impact of VCG and CpG adjuvants on protective immunity following IN mucosal and IM systemic delivery of EB formulated in chitosan hydrogel/microspheres. Immunologic analysis revealed that IN immunization in the presence of VCG induced higher levels of IFN-γ response than IM delivery or the CpG adjuvanted groups. Also, vaccine efficacy evaluation showed enhanced pharyngeal bacterial clearance and protection against lung lesions with the VCG adjuvanted vaccine formulation, thereby establishing the superior adjuvanticity of VCG over CpG. We next evaluated the impact of different concentrations of VCG on protective immunity following IN mucosal immunization. Interestingly, the adjuvanticity of VCG was concentration-dependent, since protective immunity induced following IN mucosal immunization showed dose-dependent immune responses and protection. These studies reveal that formulation of inactivated chlamydial antigens with adjuvants, such as VCG and chitosan increases their ability to induce protective immune responses against challenge.

Using Epidemiology, Immunology, and Genomics to Study the Biology of Chlamydia trachomatis

ABSTRACT

The traditional framework in which to study the biology of human infectious diseases involves characterizing interactions and features of the host, pathogen, and environment. Using the tools of epidemiology, immunology, and genomics allows one to study the biology of infectious disease within this framework. The study of Chlamydia trachomatis biology vividly illustrates the usefulness for the approach. I note key findings from my own studies on C. trachomatis epidemiology, immunology, and genomics to show how important light has been shed on its biology and how this has impacted the Chlamydia field generally. In particular, the epidemiology of C. trachomatis diseases in women shows its impact on reproduction and how public health programs to detect and treat infection has reduced that impact but at the cost of arresting the development of protective immunity and increasing the risk of infection and reinfection. Immunological studies demonstrate the importance of CD4 Th1 cells in protection and that antibiotic treatment interferes with the development of protective immunity when given early in the course of infection. Evaluating the T-cell antigen landscape for C. trachomatis and Chlamydia muridarum demonstrates the role of surface proteins such as the major outer-membrane protein and the polymorphic membrane proteins as major protective CD4 T-cell antigens. Genomic studies reveal that the genome of organism has 3 loci of immunological interest. The antigen loci of the major outer-membrane protein and polymorphic membrane proteins are hotspots for both mutation and recombination, and the plasticity zone contains immune evasion genes that are highly variable from species to species. Interestingly, these 3 loci seem to have entered the Chlamydia phylum at the time of the evolution of the Chlamydiaceae when they became pathogens of vertebrates and encountered the adaptive immune system. In aggregate, these 3 approaches have shed light on human C. trachomatis infections and suggest paths for vaccine development. These approaches are likely to remain useful for the further study of C. trachomatis and for other human pathogens.

The Koala Immune Response to Chlamydial Infection and Vaccine Development-Advancing Our Immunological Understanding

Simple Summary

Chlamydia is a major pathogen of the Australian marsupial, the koala (Phascolarctos cinereus). One approach to improving this situation is to develop a vaccine. Human Chlamydia research suggests that an effective anti-chlamydial response will involve a balance between a cell-mediated Th1 response and a humoral Th2 responses, involving systemic IgG and mucosal IgA. Characterization of koalas with chlamydial disease suggests that increased expression for similar immunological pathways and monitoring of koalas’ post-vaccination can be successful and subsequently lead to improved vaccines. These findings offer optimism that a chlamydial vaccine for wider distribution to koalas is not far off.

Abstract

Chlamydia is a significant pathogen for many species, including the much-loved Australian marsupial, the koala (Phascolarctos cinereus). To combat this situation, focused research has gone into the development and refinement of a chlamydial vaccine for koalas. The foundation of this process has involved characterising the immune response of koalas to both natural chlamydial infection as well as vaccination. From parallels in human and mouse research, it is well-established that an effective anti-chlamydial response will involve a balance of cell-mediated Th1 responses involving interferon-gamma (IFN-γ), humoral Th2 responses involving systemic IgG and mucosal IgA, and inflammatory Th17 responses involving interleukin 17 (IL-17) and neutrophils. Characterisation of koalas with chlamydial disease has shown increased expression within all three of these major immunological pathways and monitoring of koalas’ post-vaccination has detected further enhancements to these key pathways. These findings offer optimism that a chlamydial vaccine for wider distribution to koalas is not far off. Recent advances in marsupial genetic knowledge and general nucleic acid assay technology have moved koala immunological research a step closer to other mammalian research systems. However, koala-specific reagents to directly assay cytokine levels and cell-surface markers are still needed to progress our understanding of koala immunology.

Chlamydia-Specific IgA Secretion in the Female Reproductive Tract Induced via Per-Oral Immunization Confers Protection against Primary Chlamydia Challenge

Chlamydia trachomatis is an obligate intracellular pathogen that causes sexually transmitted disease. In women, chlamydial infections may cause pelvic inflammatory disease (PID), ectopic pregnancy, and infertility. The role of antibodies in protection against a primary Chlamydia infection is unclear and was a focus of this work. Using the C. muridarum mouse infection model, we show that intestinal mucosa is infected via intranasal (i.n.) or per-oral (p.o.) Chlamydia inoculation and that unlike the female reproductive tract (FRT) mucosa, it halts systemic Chlamydia dissemination. Moreover, p.o. immunization or infection with Chlamydia confers protection against per-vaginal (p.v.) challenge, resulting in significantly decreased bacterial burden in the FRT, accelerated Chlamydia clearance, and reduced hydrosalpinx pathology. In contrast, subcutaneous (s.c.) immunization conferred no protection against the p.v. challenge. Both p.o. and s.c. immunizations induced Chlamydia-specific serum IgA. However, IgA was found only in the vaginal washes and fecal extracts of p.o.-immunized animals. Following a p.v. challenge, unimmunized control and s.c.-s.c.-immunized animals developed Chlamydia-specific intestinal IgA yet failed to develop IgA in the FRT, indicating that IgA response in the FRT relies on the FRT to gastrointestinal tract (GIT) antigen transport. Vaginal secretions of p.o.-immunized animals neutralize Chlamydia in vivo, resulting in significantly lower Chlamydia burden in the FRT and Chlamydia transport to the GIT. We also show that infection of the GIT is not necessary for induction of protective immunity in the FRT, a finding that is important for the development of p.o. subunit vaccines to target Chlamydia and possibly other sexually transmitted pathogens.

Discordance in the Epithelial Cell-Dendritic Cell Major Histocompatibility Complex Class II Immunoproteome: Implications for Chlamydia Vaccine Development

BACKGROUND

Chlamydia trachomatis and Chlamydia muridarum are intracellular bacterial pathogens of mucosal epithelial cells. CD4 T cells and major histocompatibility complex (MHC) class II molecules are essential for protective immunity against them. Antigens presented by dendritic cells (DCs) expand naive pathogen-specific T cells (inductive phase), whereas antigens presented by epithelial cells identify infected epithelial cells as targets during the effector phase. We previously showed that DCs infected by C trachomatis or C muridarum present epitopes from a limited spectrum of chlamydial proteins recognized by Chlamydia-specific CD4 T cells from immune mice.

METHODS

We hypothesized that Chlamydia-infected DCs and epithelial cells present overlapping sets of Chlamydia-MHC class II epitopes to link inductive and effector phases to generate protective immunity. We tested that hypothesis by infecting an oviductal epithelial cell line with C muridarum, followed by immunoaffinity isolation and sequencing of MHC class I- and II-bound peptides.

RESULTS

We identified 26 class I-bound and 4 class II-bound Chlamydia-derived peptides from infected epithelial cells. We were surprised to find that none of the epithelial cell class I- and class II-bound chlamydial peptides overlapped with peptides presented by DCs.

CONCLUSIONS

We suggest the discordance between the DC and epithelial cell immunoproteomes has implications for delayed clearance of Chlamydia and design of a Chlamydia vaccine.

Analysis of complement deposition and processing on Chlamydia trachomatis

Chlamydia trachomatis (C. trachomatis) is the leading cause of sexually transmitted bacterial infections worldwide, with over 120 million annual cases. C. trachomatis infections are associated with severe reproductive complications in women such as extrauterine pregnancy and tubal infertility. The infections are often long lasting, associated with immunopathology, and fail to elicit protective immunity which makes recurrent infections common. The immunological mechanisms involved in C. trachomatis infections are only partially understood. Murine infection models suggest that the complement system plays a significant role in both protective immunity and immunopathology during primary Chlamydia infections. However, only limited structural and mechanistic evidence exists on complement-mediated immunity against C. trachomatis. To expand our current knowledge on this topic, we analyzed global complement deposition on C. trachomatis using comprehensive in-depth mass spectrometry-based proteomics. We show that factor B, properdin, and C4b bind to C. trachomatis demonstrating that C. trachomatis-induced complement activation proceeds through at least two activation pathways. Complement activation leads to cleavage and deposition of C3 and C5 activation products, causing initiation of the terminal complement pathway and deposition of C5b, C6, C7, C8, C9 on C. trachomatis. Interestingly, using immunoelectron microscopy, we show that C5b-9 deposition occurred sporadically and only in rare cases formed complete lytic terminal complexes, possibly caused by the presence of the negative regulators vitronectin and clusterin. Finally, cleavage analysis of C3 demonstrated that deposited C3b is degraded to the opsonins iC3b and C3dg and that this complement opsonization facilitates C. trachomatis binding to human B-cells.

Chlamydia trachomatis L2c Infection in a Porcine Model Produced Urogenital Pathology and Failed to Induce Protective Immune Responses Against Re-Infection

The current study was designed to evaluate the pathogenesis, pathology and immune response of female genital tract infection with Chlamydia trachomatis L2c, the most recently discovered lymphogranuloma venereum strain, using a porcine model of sexually transmitted infections. Pigs were mock infected, infected once or infected and re-infected intravaginally, and samples were obtained for chlamydial culture, gross and microscopic pathology, and humoral and cell-mediated immunity. Intravaginal inoculation of pigs with this bacterium resulted in an infection that was confined to the urogenital tract, where inflammation and pathology were caused that resembled what is seen in human infection. Re-infection resulted in more severe gross pathology than primary infection, and chlamydial colonization of the urogenital tract was similar for primary infected and re-infected pigs. This indicates that primary infection failed to induce protective immune responses against re-infection. Indeed, the proliferative responses of mononuclear cells from blood and lymphoid tissues to C. trachomatis strain L2c were never statistically different among groups, suggesting that C. trachomatis-specific lymphocytes were not generated following infection or re-infection. Nevertheless, anti-chlamydial antibodies were elicited in sera and vaginal secretions after primary infection and re-infection, clearly resulting in a secondary systemic and mucosal antibody response. While primary infection did not protect against reinfection, the porcine model is relevant for evaluating immune and pathogenic responses for emerging and known C. trachomatis strains to advance drug and/or vaccine development in humans.

Use of Chlamydial Elementary Bodies as Probes to Isolate Pathogen-Specific Human Monoclonal Antibodies

Chlamydia trachomatis is one of the most prevalent sexually transmitted infectious agents in the world and the leading cause of infectious blindness. The role of antibodies in the prevention and clearance of infection is still not fully understood, but the analysis of the immunoglobulin response to novel vaccine candidates is an important part of many of these studies. In this chapter, we describe a novel method to identify and isolate Chlamydia-specific memory B cells by fluorescence-activated cell sorting (FACS) using fluorescently labeled whole bacteria from cryopreserved human PBMC samples. This method allows for live single cells to be sorted for cell culture, in vitro assays, single-cell RNA sequencing, and cloning of paired heavy and light chains for recombinant monoclonal antibody production.

Shift work influences the outcomes of Chlamydia infection and pathogenesis

Shift work, performed by approximately 21 million Americans, is irregular or unusual work schedule hours occurring after 6:00 pm. Shift work has been shown to disrupt circadian rhythms and is associated with several adverse health outcomes and chronic diseases such as cancer, gastrointestinal and psychiatric diseases and disorders. It is unclear if shift work influences the complications associated with certain infectious agents, such as pelvic inflammatory disease, ectopic pregnancy and tubal factor infertility resulting from genital chlamydial infection. We used an Environmental circadian disruption (ECD) model mimicking circadian disruption occurring during shift work, where mice had a 6-h advance in the normal light/dark cycle (LD) every week for a month. Control group mice were housed under normal 12/12 LD cycle. Our hypothesis was that compared to controls, mice that had their circadian rhythms disrupted in this ECD model will have a higher Chlamydia load, more pathology and decreased fertility rate following Chlamydia infection. Results showed that, compared to controls, mice that had their circadian rhythms disrupted (ECD) had higher Chlamydia loads, more tissue alterations or lesions, and lower fertility rate associated with chlamydial infection. Also, infected ECD mice elicited higher proinflammatory cytokines compared to mice under normal 12/12 LD cycle. These results imply that there might be an association between shift work and the increased likelihood of developing more severe disease from Chlamydia infection.

HIV, progestins, genital epithelial barrier function, and the burden of objectivity†

Contributions from a diverse set of scientific disciplines will be needed to help individuals make fully informed decisions regarding contraceptive choices least likely to promote HIV susceptibility. This commentary recaps contrasting interpretations of results from the Evidence for Contraceptive Options and HIV Outcomes (ECHO) Trial, a study that compared HIV risk in women using the progestin-only injectable contraceptive depot medroxyprogesterone acetate (DMPA) vs. two other contraceptive choices. It also summarizes results from basic and translational research that establish biological plausibility for earlier clinical studies that identified enhanced HIV susceptibility in women using DMPA.

NK Cells Contribute to Protective Memory T Cell Mediated Immunity to Chlamydia muridarum Infection

We previously reported that NK cells can promote type 1 T cell immune response that is essential for protection to a primary infection of Chlamydia muridarum. In this study, we have investigated the contribution of NK cells to memory T cells associated immunity during chlamydial infection. We have found that NK cell depletion led to impaired production of IFN-γ by memory T cells upon re-stimulation with chlamydial antigens in vitro. Mice with depleted NK cells also exhibited reduced type 1 T cell recall responses, with increased production of IL-4 from CD4⁺ T cells and a lower level of Chlamydia-specific IgG2a titers compared to control mice. In addition, Tregs response was significantly increased in mice with NK cell depletion. Moreover, NK cell-depleted mice showed an increased bacterial loads and more severe inflammatory pathological changes than control mice. These findings indicate that NK cells contribute to protective memory T cell associated immunity to chlamydial re-infection through modulating the cytokine pattern of T cell and inhibition of Tregs response.

Antibody, but not B-cell-dependent antigen presentation, plays an essential role in preventing Chlamydia systemic dissemination in mice

The obligate intracellular bacterium Chlamydia trachomatis causes the most prevalent bacterial sexually transmitted infection worldwide. CD4 T cells play a central role in the protective immunity against Chlamydia female reproductive tract (FRT) infection, while B cells are thought to be dispensable for resolution of primary Chlamydia infection in mouse models. We recently reported an unexpected requirement of B cells in local Chlamydia-specific CD4 T-cell priming and bacterial containment within the FRT. Here, we sought to tackle the precise effector function of B cells during Chlamydia primary infection. Using mixed bone marrow chimeras that lack B-cell-dependent Ag presentation (MHCII^B - / - ) or devoid of circulating antibodies (AID^-/- × μS^-/- ), we show that Chlamydia-specific CD4 T-cell expansion does not rely on Ag presentation by B cells. Importantly, we demonstrate that antibody, but not B-cell-dependent Ag presentation, is required for preventing systemic bacterial dissemination following Chlamydia FRT infection.

Comparison of Chlamydia outer membrane complex to recombinant outer membrane proteins as vaccine

The Chlamydial outer membrane complex (COMC) from the elementary body (EB) is a protein rich insoluble outer membrane shell from which cytosolic proteins have been extracted with detergent. In this study we conducted mass spectrometry experiments to detect proteins in the COMC prepared from C. muridarum EB. Proteomic analysis showed that the COMC contained 75 proteins that included 10 outer membrane proteins (OMPs) such as the major outer membrane protein (MOMP) and polymorphic membrane proteins (Pmps) that were previously identified as CD4 T cell vaccine candidates. We tested the vaccine efficacy of COMC in comparison to individual or combination of recombinant OMPs formulated with Th1 polarizing adjuvant DDA/MPL in two murine genital tract models (C. muridarum and C. trachomatis) by measuring organismal shedding, tubal pathology and immune responses including neutralizing antibodies. In the C. muridarum model, the COMC vaccine generated broadly reactive immune responses against multiple outer membrane proteins, high levels of EB binding and neutralizing antibody and exhibited superior protection against genital infection and pathology when compared to the recombinant PmpG vaccine. Denaturing the COMC by boiling significantly reduced protection. In the C. trachomatis model, the COMC vaccine also conferred greater protection compared to individual or multiple recombinant outer membrane proteins. Immunization with multiple COMCs from C. trachomatis serovars D, F and J generated neutralizing antibodies against multiple C. trachomatis serovars. We conclude that broader immunogenicity and generation of neutralizing antibody may explain the superior efficacy of COMC vaccine. The study suggests that conformationally intact proteins will be necessary for a successful recombinant OMP vaccine.

Exogenous oestrogen inhibits genital transmission of cell-associated HIV-1 in DMPA-treated humanized mice

Introduction

HIV affects more women than any other life‐threatening infectious agent, and most infections are sexually transmitted. HIV must breach the female genital tract mucosal barrier to establish systemic infection, and clinical studies indicate virus more easily evades this barrier in women using depot‐medroxyprogesterone acetate (DMPA) and other injectable progestins for contraception. Identifying a potential mechanism for this association, we learned DMPA promotes susceptibility of wild‐type mice to genital herpes simplex virus type 2 (HSV‐2) infection by reducing genital tissue expression of the cell‐cell adhesion molecule desmoglein‐1 (DSG‐1) and increasing genital mucosal permeability. Conversely, DMPA‐mediated increases in genital mucosal permeability and HSV‐2 susceptibility were eliminated in mice concomitantly administered exogenous oestrogen (E). To confirm and extend these findings, herein we used humanized mice to define effects of systemic DMPA and intravaginal (ivag) E administration on susceptibility to genital infection with cell‐associated HIV‐1.

Methods

Effects of DMPA or an intravaginal (ivag) E cream on engraftment of NOD‐scid‐IL‐2Rgc^null (NSG) mice with human peripheral blood mononuclear cells (hPBMCs) were defined with flow cytometry. Confocal microscopy was used to evaluate effects of DMPA, DMPA and E cream, or DMPA and the pharmacologically active component of the cream on vaginal tissue DSG‐1 expression and genital mucosal permeability to low molecular weight (LMW) molecules and hPBMCs. In other studies, hPBMC‐engrafted NSG mice (hPBMC‐NSG) received DMPA or DMPA and ivag E cream before genital inoculation with 10⁶ HIV‐1‐infected hPBMCs. Mice were euthanized 10 days after infection, and plasma HIV‐1 load quantified by qRT‐PCR and splenocytes used to detect HIV‐1 p24 antigen via immunohistochemistry and infectious virus via TZM‐bl luciferase assay.

Results

Whereas hPBMC engraftment was unaffected by DMPA or E treatment, mice administered DMPA and E (cream or the pharmacologically active cream component) displayed greater vaginal tissue expression of DSG‐1 protein and decreased vaginal mucosal permeability to LMW molecules and hPBMCs versus DMPA‐treated mice. DMPA‐treated hPBMC‐NSG mice were also uniformly susceptible to genital transmission of cell‐associated HIV‐1, while no animal concomitantly administered DMPA and E cream acquired systemic HIV‐1 infection.

Conclusion

Exogenous E administration reduces susceptibility of DMPA‐treated humanized mice to genital HIV‐1 infection.

Co-delivery of amphipol-conjugated adjuvant with antigen, and adjuvant combinations, enhance immune protection elicited by a membrane protein-based vaccine against a mucosal challenge with Chlamydia

INTRODUCTION

Chlamydial infections are spread worldwide and a vaccine is needed to control this pathogen. The goals of this study were to determine if the delivery of an adjuvant associated to the antigen, via a derivatized amphipol, and adjuvant combinations improve vaccine protection.

METHODS

A novel approach, trapping the Chlamydia muridarum (Cm) native MOMP (nMOMP) with amphipols (A8-35), bearing a covalently conjugated peptide (EP67), was used. Adjuvants incorporated were: EP67 either conjugated to A8-35, which was used to trap nMOMP (nMOMP/EP67-A8-35), or free as a control, added to nMOMP/A8-35 complexes (nMOMP/A8-35+EP67); Montanide ISA 720 to enhance humoral responses, and CpG-1826 to elicit robust cell-mediated immunity (CMI). BALB/c mice were immunized by mucosal and systemic routes. Intranasal immunization with live Cm was used as positive control and three negative controls were included. Mice were challenged intranasally with Cm and changes in body weight, lungs weight and number of Cm-inclusion forming units (IFU) recovered from the lungs were evaluated to establish protection. To assess local responses levels of IFN- γ and Cm-specific IgA were determined in lungs' supernatants.

RESULTS

Structural assays demonstrated that nMOMP secondary structure and thermal stability were maintained when A8-35 was covalently modified. Mice vaccinated with nMOMP/EP67-A8-35 were better protected than animals immunized with nMOMP/A8-35+EP67. Addition of Montanide enhanced Th2 responses and improved protection. Including CpG-1826 further broadened, intensified and switched to Th1-biased immune responses. With delivery of nMOMP and the three adjuvants, as determined by changes in body weight, lungs weight and number of IFU recovered from lungs, protection at 10 days post-challenge was equivalent to that induced by immunization with live Cm.

CONCLUSIONS

Covalent association of EP67 to A8-35, used to keep nMOMP water-soluble, improves protection over that conferred by free EP67. Adjuvant combinations including EP67+Montanide+CpG-1826, by broadening and intensifying cellular and humoral immune responses, further enhanced protection.

The Chlamydia M278 Major Outer Membrane Peptide Encapsulated in the Poly(lactic acid)-Poly(ethylene glycol) Nanoparticulate Self-Adjuvanting Delivery System Protects Mice Against a Chlamydia muridarum Genital Tract Challenge by Stimulating Robust Systemic and Local Mucosal Immune Responses

Recently, we reported that our PPM chlamydial nanovaccine [a biodegradable co-polymeric PLA-PEG (poly(lactic acid)-poly(ethylene glycol))-encapsulated M278 peptide (derived from the major outer membrane protein (MOMP) of Chlamydia)] exploits the caveolin-mediated endocytosis pathway for endosomal processing and MHC class II presentation to immune-potentiate Chlamydia-specific CD4⁺ T-cell immune effector responses. In the present study, we employed the Chlamydia muridarum mouse infection model to evaluate the protective efficacy of PPM against a genital tract challenge. Our results show that mice immunized with PPM were significantly protected against a homologous genital tract challenge evidently by reduced vaginal bacterial loads. Protection of mice correlated with enhanced Chlamydia-specific adaptive immune responses predominated by IFN-γ along with CD4⁺ T-cells proliferation and their differentiation to CD4⁺ memory (CD44^high CD62L^high) and effector (CD44^high CD62L^low) T-cell phenotypes. We observed the elevation of M278- and MOMP-specific serum antibodies with high avidity in the ascending order IgG1 > IgG2b > IgG2a. A key finding was the elevated mucosal IgG1 and IgA antibody titers followed by an increase in MOMP-specific IgA after the challenge. The Th1/Th2 antibody titer ratios (IgG2a/IgG1 and IgG2b/IgG1) revealed that PPM evoked a Th2-directed response, which skewed to a Th1-dominated antibody response after the bacterial challenge of mice. In addition, PPM immune sera neutralized the infectivity of C. muridarum in McCoy cells, suggesting the triggering of functional neutralizing antibodies. Herein, we reveal for the first time that subcutaneous immunization with the self-adjuvanting biodegradable co-polymeric PPM nanovaccine immune-potentiated robust CD4⁺ T cell-mediated immune effector responses; a mixed Th1 and Th2 antibody response and local mucosal IgA to protect mice against a chlamydial genital tract challenge.

Diversity in the T cell response to Chlamydia-sum are better than one

Chlamydia trachomatis is responsible for an increasing number of sexually transmitted infections in the United States and is a common cause of serious pathology in the female reproductive tract (FRT). Given the impact and incidence of these infections, the production of an effective Chlamydia vaccine is a public health priority. Mouse models of Chlamydia infection have been utilized to develop a detailed and mechanistic understanding of protective immunity in the FRT. These studies reveal that MHC class-II restricted Chlamydia-specific CD4 T cells are critical for primary bacterial clearance and provide effective protection against secondary infection in the FRT. Despite the clear importance of IFN- γ produced by CD4 Th1 cells, there are also suggestions of wider functional heterogeneity in the CD4 T cell response to Chlamydia infection. Understanding the role of this diversity in the CD4 T helper cell response in the FRT should allow a more nuanced view of CD4 T cell biology in the context of Chlamydia infection and may be critical for vaccine development. Here, we summarize our current understanding of CD4 T helper subsets in the clearance of Chlamydia and discuss some areas where knowledge needs to be further extended by additional experimentation.

T Cell-Independent Gamma Interferon and B Cells Cooperate To Prevent Mortality Associated with Disseminated Chlamydia muridarum Genital Tract Infection

CD4 T cells and antibody are required for optimal acquired immunity to Chlamydia muridarum genital tract infection, and T cell-mediated gamma interferon (IFN-γ) production is necessary to clear infection in the absence of humoral immunity. However, the role of T cell-independent immune responses during primary infection remains unclear. We investigated this question by inoculating wild-type and immune-deficient mice with C. muridarum CM001, a clonal isolate capable of enhanced extragenital replication. Genital inoculation of wild-type mice resulted in transient dissemination to the lungs and spleen that then was rapidly cleared from these organs. However, CM001 genital infection proved lethal for STAT1-/- and IFNG-/- mice, in which IFN-γ signaling was absent, and for Rag1-/- mice, which lacked T and B cells and in which innate IFN-γ signaling was retained. In contrast, B cell-deficient muMT mice, which can generate a Th1 response, and T cell-deficient mice with intact B cell and innate IFN-γ signaling survived. These data collectively indicate that IFN-γ prevents lethal CM001 dissemination in the absence of T cells and suggests a B cell corequirement. Adoptive transfer of convalescent-phase immune serum but not naive IgM to Rag1-/- mice infected with CM001 significantly increased the survival time, while transfer of naive B cells completely rescued Rag1-/- mice from CM001 lethality. Protection was associated with a significant reduction in the lung chlamydial burden of genitally infected mice. These data reveal an important cooperation between T cell-independent B cell responses and innate IFN-γ in chlamydial host defense and suggest that interactions between T cell-independent antibody and IFN-γ are essential for limiting extragenital dissemination.

In silico prediction of T- and B-cell epitopes in PmpD: First step towards to the design of a Chlamydia trachomatis vaccine

BACKGROUND

Chlamydia trachomatis is the most common sexually transmitted bacterial infection globally. Currently, there are no vaccines available despite the efforts made to develop a protective one. Polymorphic membrane protein D (PmpD) is an attractive immunogen candidate as it is conserved among strains and it is target of neutralizing antibodies. However, its high molecular weight and its complex structure make it difficult to handle by recombinant DNA techniques. Our aim is to predict B-cell and T-cell epitopes of PmpD.

METHOD

A sequence (Genbank AAK69391.2) having 99-100% identity with various serovars of C. trachomatis was used for predictions. NetMHC and NetMHCII were used for T-cell epitope linked to MHC I or MHC II alleles prediction, respectively. BepiPred predicted linear B-cell epitopes. For three dimensional epitopes, PmpD was homology-modeled by Raptor X. Surface epitopes were predicted on its globular structure using DiscoTope.

RESULTS

NetMHC predicted 271 T-cell epitopes of 9-12aa with weak affinity, and 70 with strong affinity to MHC I molecules. NetMHCII predicted 2903 T-cell epitopes of 15aa with weak affinity, and 742 with strong affinity to MHC II molecules. Twenty four linear B-cell epitopes were predicted. Raptor X was able to model 91% of the three-dimensional structure whereas 57 residues of discontinuous epitopes were suggested by DiscoTope. Six regions containing B-cell and T-cell epitopes were identified by at least two predictors.

CONCLUSIONS

PmpD has potential B-cell and T-cell epitopes distributed throughout the sequence. Thus, several fragments were identified as valuable candidates for subunit vaccines against C. trachomatis.

Oral Chlamydia vaccination induces transmucosal protection in the airway

Although Chlamydia has been frequently detected in the gastrointestinal tracts of both humans and animals, it is not associated with any gastrointestinal pathology. We have recently shown that gastrointestinal Chlamydiamuridarum is not only non-pathogenic but also induces protective immunity in the genital tract. We now report that the transmucosal immunity induced by a single oral immunization with C.muridarum protected the mouse airway from a subsequent challenge infection. The oral immunization significantly reduced chlamydial burden in the airway as early as day 3 after intranasal challenge. As a result, the airway chlamydial spreading to extra-airway tissues was completely prevented on day 3 and significantly reduced on day 9. The immunized mice were protected from any significant systemic toxicity caused by the intranasal challenge since there was no significant bodyweight drop in the immunized mice. This robust protection correlated well with Chlamydia-specific antibodies that recognize chlamydial organism surface antigens and T cell responses that are dominated with a Th1 phenotype. The immunized mice developed high ratios of IgG2b/c over IgG1 levels and IFNγ-producing over IL-5- or IL-13-producing lymphocytes. Thus, we have demonstrated that oral vaccination with C. muridarum can induce Th1-dominant transmucosal immunity in the airway. Together with previous studies, we propose that non-pathogenic colonization of Chlamydia in the gastrointestinal tract be explored as an oral delivery system for inducing protection against infections and pathologies in extra-gastrointestinal tissues.

B Cell Presentation of Chlamydia Antigen Selects Out Protective CD4γ13 T Cells: Implications for Genital Tract Tissue-Resident Memory Lymphocyte Clusters

Surveillance and defense of the enormous mucosal interface with the nonsterile world are critical to protecting the host from a wide range of pathogens. Chlamydia trachomatis is an intracellular bacterial pathogen that replicates almost exclusively in the epithelium of the reproductive tract. The fallopian tubes and vagina are poorly suited to surveillance and defense, with limited immune infrastructure positioned near the epithelium. However, a dynamic process during clearing primary infections leaves behind new lymphoid clusters immediately beneath the epithelium. These memory lymphocyte clusters (MLCs) harboring tissue-resident memory (Trm) T cells are presumed to play an important role in protection from subsequent infections. Histologically, human Chlamydia MLCs have prominent B cell populations. We investigated the status of genital tract B cells during C. muridarum infections and the nature of T cells recovered from immune mice using immune B cells as antigen-presenting cells (APCs). These studies revealed a genital tract plasma B cell population and a novel genital tract CD4 T cell subset producing both gamma interferon (IFN-γ) and interleukin-13 (IL-13). A panel of CD4 T cell clones and microarray analysis showed that the molecular fingerprint of CD4γ13 T cells includes a Trm-like transcriptome. Adoptive transfer of a Chlamydia-specific CD4γ13 T cell clone completely prevented oviduct immunopathology without accelerating bacterial clearance. Existence of a CD4γ13 T cell subset provides a plausible explanation for the observation that human peripheral blood mononuclear cell (PBMC) Chlamydia-specific IFN-γ and IL-13 responses predict resistance to reinfection.

Structural and Immunological Characterization of Novel Recombinant MOMP-Based Chlamydial Antigens

Chlamydia is the most common cause of bacterial sexually transmitted infections worldwide. While infections resolve with antibiotic treatment, this is often neglected in women due to frequent asymptomatic infections, leading to disease progression and severe sequelae (pelvic inflammatory disease, ectopic pregnancy, infertility). Development of a vaccine against Chlamydia is crucial. Whole organism-based vaccines have short-lived activity, serovar/subgroup-specific immunity and can cause adverse reactions in vaccinated subjects. The Chlamydia major outer membrane protein (MOMP) is a prime candidate for a subunit vaccine. MOMP contains four regions of sequence variability (variable domains, VDs) with B-cell and T-cell epitopes that elicit protective immunity. However, barriers for developing a MOMP-based vaccine include solubility, yield and refolding. We have engineered novel recombinant antigens in which the VDs are expressed into a carrier protein structurally similar to MOMP and suitable for recombinant expression at a high yield in a correctly folded and detergent-free form. Using a carrier such as the PorB porin from the human commensal organism N. lactamica, we show that PorB/VD chimeric proteins are immunogenic, antigenic and cross-reactive with MOMP. VDs are unique for each serovar but if combined in a single vaccine, a broad coverage against the major Chlamydia serovars can be ensured.

Protective Effect of Vaccine Promoted Neutralizing Antibodies against the Intracellular Pathogen Chlamydia trachomatis

There is an unmet need for a vaccine to control Chlamydia trachomatis (C.t.) infections. We have recently designed a multivalent heterologous immuno-repeat 1 (Hirep1) vaccine construct based on major outer membrane protein variable domain (VD) 4 regions from C.t. serovars (Svs) D–F. Hirep1 administered in the Cationic Adjuvant Formulation no. 1 (CAF01) promoted neutralizing antibodies in concert with CD4⁺ T cells and protected against genital infection. In the current study, we examined the protective role of the antibody (Ab) response in detail. Mice were vaccinated with either Hirep1 or a vaccine construct based on a homologous multivalent construct of extended VD4’s from SvF (extVD4^F*4), adjuvanted in CAF01. Hirep1 and extVD4^F*4 induced similar levels of Ab and cell-mediated immune responses but differed in the fine specificity of the B cell epitopes targeted in the VD4 region. Hirep1 induced a strong response toward a neutralizing epitope (LNPTIAG) and the importance of this epitope for neutralization was demonstrated by competitive inhibition with the corresponding peptide. Immunization with extVD4^F*4 skewed the response to a non-neutralizing epitope slightly upstream in the sequence. Vaccination with Hirep1 as opposed to extVD4^F*4 induced significant protection against infection in mice both in short- and long-term vaccination experiments, signifying a key role for Hirep1 neutralizing antibodies during protection against C.t. Finally, we show that passive immunization of Rag1 knockout mice with Hirep1 antibodies completely prevented the establishment of infection in 48% of the mice, demonstrating an isolated role for neutralizing antibodies in controlling infection. Our data emphasize the role of antibodies in early protection against C.t. and support the inclusion of neutralizing targets in chlamydia vaccines.

IL-6-mediated signaling pathways limit Chlamydia muridarum infection and exacerbate its pathogenicity in the mouse genital tract

Chlamydia muridarum induction of mouse hydrosalpinx, depending on both tubal infection and inflammation, has been used for investigating Chlamydia trachomatis pathogenesis. We now report that IL-6 both inhibits C. muridarum infection and exacerbates pathogenicity in the mouse genital tract. When intravaginally inoculated with a high dose of C. muridarum, IL-6-deficient mice developed more extensive genital tract infection with severe hydrosalpinx, suggesting that IL-6 is required for controlling the high dose infection but not essential for C. muridarum-induced pathology. However, at a low dose, IL-6-deficient mice still developed more extensive infection in the genital tract but no longer with significant pathology, suggesting that IL-6 is required for both controlling the low dose infection and exacerbating the low dose infection-induced pathology. The lack of hydrosalpinx in IL-6-deficient mice correlated with significantly reduced inflammatory infiltration in the oviduct tissue and decreased spleen CD4+ and CD8+ T cells that produce TNFα. Thus, IL-6-dependent pathways are important for both limiting chlamydial colonization in the genital tract mucosal tissues regardless of the infection doses and exacerbating chlamydial pathogenicity in the upper genital tract when IL-6-independent pathogenic mechanisms are not yet activated with a low infection dose.

A Chlamydia-Specific TCR-Transgenic Mouse Demonstrates Th1 Polyfunctionality with Enhanced Effector Function

Chlamydia is responsible for millions of new infections annually, and current efforts focus on understanding cellular immunity for targeted vaccine development. The Chlamydia-specific CD4 T cell response is characterized by the production of IFN-γ, and polyfunctional Th1 responses are associated with enhanced protection. A major limitation in studying these responses is the paucity of tools available for detection, quantification, and characterization of polyfunctional Ag-specific T cells. We addressed this problem by developing a TCR-transgenic (Tg) mouse with CD4 T cells that respond to a common Ag in Chlamydia muridarum and Chlamydia trachomatis Using an adoptive-transfer approach, we show that naive Tg CD4 T cells become activated, proliferate, migrate to the infected tissue, and acquire a polyfunctional Th1 phenotype in infected mice. Polyfunctional Tg Th1 effectors demonstrated enhanced IFN-γ production compared with polyclonal cells, protected immune-deficient mice against lethality, mediated bacterial clearance, and orchestrated an anamnestic response. Adoptive transfer of Chlamydia-specific CD4 TCR-Tg T cells with polyfunctional capacity offers a powerful approach for analysis of protective effector and memory responses against chlamydial infection and demonstrates that an effective monoclonal CD4 T cell response may successfully guide subunit vaccination strategies.

Neutrophils Are Central to Antibody-Mediated Protection against Genital Chlamydia

Determining the effector populations involved in humoral protection against genital chlamydia infection is crucial to development of an effective chlamydial vaccine. Antibody has been implicated in protection studies in multiple animal models, and we previously showed that the passive transfer of immune serum alone does not confer immunity in the mouse. Using the Chlamydia muridarum model of genital infection, we demonstrate a protective role for both Chlamydia-specific immunoglobulin G (IgG) and polymorphonuclear neutrophils and show the importance of an antibody/effector cell interaction in mediating humoral immunity. While neutrophils were found to contribute significantly to antibody-mediated protection in vivo, natural killer (NK) cells were dispensable for protective immunity. Furthermore, gamma interferon (IFN-γ)-stimulated primary peritoneal neutrophils (PPNs) killed chlamydiae in vitro in an antibody-dependent manner. The results from this study support the view that an IFN-γ-activated effector cell population cooperates with antibody to protect against genital chlamydia and establish neutrophils as a key effector cell in this response.

Genome-wide profiling of humoral immunity and pathogen genes under selection identifies immune evasion tactics of Chlamydia trachomatis during ocular infection

The frequency and duration of Chlamydia trachomatis (Ct) ocular infections decrease with age, suggesting development of partial immunity. However, there is a lack of clear correlates of immunity to Ct infection in humans. We screened sera from a cohort of Gambian children followed for six-months against a Ct-proteome microarray. At genome sequence level, we detected signatures of selection from a population of ocular Ct isolates from Guinea-Bissau. Together these approaches allowed us to highlight the focus of humoral responses and hypothesise new modes of pathogen immune evasion. Children who were susceptible to frequent and/or prolonged Ct infection had a less focussed antibody response, including preferential recognition of forty-two antigens. There was evidence of positive and purifying selection across the genome, but little balancing selection. In contrast, most antigens that were associated with susceptibility were under neutral selection. These data suggest an evasion strategy in which Ct presents a large panel of irrelevant antigens to the immune system to block or misdirect protective responses. Development of a focused immune response, possibly induced through vaccination, may be an effective strategy to promote protection to Ct infection.

CCR7 Deficiency Allows Accelerated Clearance of Chlamydia from the Female Reproductive Tract

Immune mechanisms responsible for pathogen clearance from the female reproductive tract (FRT) are incompletely defined; in particular, the contribution of lymphocyte trafficking to this process is unclear. CCR7-deficient mice have profoundly altered lymphocyte recirculation and display ectopic formation of lymphocyte aggregates within mucosal nonlymphoid tissues, including the FRT. In this study, we investigated how altered lymphocyte distribution in CCR7-deficient mice would affect host responses to Chlamydia muridarum within the reproductive tract. As expected, CCR7-deficient mice exhibited reduced lymphocyte trafficking to lymph nodes and a corresponding increase in T cell populations within the FRT. After intravaginal infection with Chlamydia, CCR7-deficient mice displayed markedly reduced Ag-specific CD4 T cell responses within the local draining iliac lymph nodes, yet robust Th1 and Th17 responses were prominent in the FRT. In addition, Chlamydia-specific Ab responses were dysregulated in CCR7-deficient mice, displaying an unexpected increase in the systemic IgA responses. Importantly, prominent mucosal immune responses in CCR7-deficient mice increased the efficiency of bacteria clearance from the FRT while reducing tissue-associated inflammation and pathology. Thus, increased numbers of lymphocytes within the FRT result in pathogen clearance with reduced immune-mediated pathology.

A novel whole-bacterial enzyme linked-immunosorbant assay to quantify Chlamydia trachomatis specific antibodies reveals distinct differences between systemic and genital compartments

Chlamydia trachomatis (CT) is the leading sexually transmitted bacterial infection. The continued global burden of CT infection strongly predicates the need for a vaccine to supplement current chlamydial control programs. The correlates of protection against CT are currently unknown, but they must be carefully defined to guide vaccine design. The localized nature of chlamydial infection in columnar epithelial cells of the genital tract necessitates investigation of immunity at the site of infection. The purpose of this study was to develop a sensitive whole bacterial enzyme-linked immunosorbent assay (ELISA) to quantify and compare CT-specific IgG and IgA in sera and genital secretions from CT-infected women. To achieve this, elementary bodies (EBs) from two of the most common genital serovars (D and E) were attached to poly-L-lysine-coated microtiter plates with glutaraldehyde. EB attachment and integrity were verified by the presence of outer membrane antigens and the absence of bacterial cytoplasmic antigens. EB-specific IgG and IgA standards were developed by pooling sera with high titers of CT-specific antibodies from infected women. Serum, endocervical and vaginal secretions, and endocervical cytobrush specimens from CT-infected women were used to quantify CT-specific IgG and IgA which were then normalized to total IgG and IgA, respectively. Analyses of paired serum and genital samples revealed significantly higher proportions of EB-specific antibodies in genital secretions compared to sera. Cervical and vaginal secretions and cytobrush specimens had similar proportions of EB-specific antibodies, suggesting any one of these genital sampling techniques could be used to quantify CT-specific antibodies when appropriate normalization methodologies are implemented. Overall, these results illustrate the need to investigate genital tract CT antibody responses, and our assay provides a useful quantitative tool to assess natural immunity in defined clinical groups and CT vaccine trials.

Molecular cloning, characterization and functional analysis of a putative mitogen-activated protein kinase kinase kinase 4 (MEKK4) from blood clam Tegillarca granosa

The mitogen-activated protein kinase (MAPK) cascades stand for one of the most important signaling mechanisms in response to environmental stimuli. In the present study, we cloned and identified for the first time the full-length cDNA of MAPK kinase kinase 4 (TgMEKK4) from Blood clam Tegillarca granosa using rapid amplification of cDNA ends method. The full-length cDNA of TgMEKK4 was of 1605 bp in length, encoding a polypeptide of 364 amino acids with a predicted molecular mass of 41.22 kDa and theoretical isoelectric point of 6.29. The conserved MEKK4-domain was identified in TgMEKK4 by SMART program analysis. Homology analysis of the deduced amino acid sequence of TgMEKK4 with other known sequences revealed that TgMEKK4 shared 58%-80% identity to MEKK4s from other species. TgMEKK4 mRNA transcripts could be detected in all tissues examined with the highest expression level in the gill by qRT-PCR. The mRNA expression of TgMEKK4 was up-regulated significantly in hemocytes after Vibrio parahaemolyticus, Vibrio alginolyticus and Lipopolysaccharide (LPS) challenges. Overexpression of TgMEKK4 in HEK 293T cells resulted in the activation of JNK and ERK, but not p38. Consistently, In vivo study indicated that LPS stimulation enhanced JNK, ERK and p38 phosphorylation in blood clams. These results suggest that TgMEKK4 is a powerful factor in the regulation of genes that may be involved in innate immune response of blood clam.

Immunization of a wild koala population with a recombinant Chlamydia pecorum Major Outer Membrane Protein (MOMP) or Polymorphic Membrane Protein (PMP) based vaccine: New insights into immune response, protection and clearance

We assessed the effects of two different single-dose anti-Chlamydia pecorum (C. pecorum) vaccines (containing either Major Outer Membrane Protein (3MOMP) or Polymorphic Membrane Protein (Pmp) as antigens) on the immune response of a group of wild koalas. Both vaccines elicited a systemic humoral response as seen by the production of anti-chlamydial IgG antibodies in more than 90% of vaccinated koalas. A mucosal immune response was also observed, with an increase in Chlamydia-specific mucosal IgG and/or IgA antibodies in some koalas post-vaccination. Both vaccines elicited a cell-mediated immune response as measured by the production of the cytokines IFN-γ and IL-17 post-vaccination. To determine the level of protection provided by the vaccines under natural conditions we assessed C. pecorum infection loads and chlamydial disease status of all vaccinated koalas pre- and post-vaccination, compared to a non-vaccinated cohort from the same habitat. The MOMP vaccinated koalas that were infected on the day of vaccination showed significant clearance of their infection at 6 months post-vaccination. In contrast, the number of new infections in the PMP vaccine was similar to the control group, with some koalas progressing to disease. Genotyping of the ompA gene from the C. pecorum strains infecting the vaccinated animals, identified genetic variants of ompA-F genotype and a new genotype ompA-O. We found that those animals that were the least well protected became infected with strains of C. pecorum not covered by the vaccine. In conclusion, a single dose vaccine formulated with either recombinant PmpG or MOMP can elicit both cell-mediated and humoral (systemic and mucosal) immune responses, with the MOMP vaccine showing clearance of infection in all infected koalas. Although the capability of our vaccines to stimulate an adaptive response and be protective needs to be fully evaluated, this work illustrates the necessity to combine epitopes most relevant to a large panel of variable strains with an efficient adjuvant.