Role of T lymphocytes in the pathogenesis of Chlamydia disease

Multi-component prime-boost Chlamydia trachomatis vaccination regimes induce antibody and T cell responses and accelerate clearance of infection in a non-human primate model

It is of international priority to develop a vaccine against sexually transmitted Chlamydia trachomatis infections to combat the continued global spread of the infection. The optimal immunization strategy still remains to be fully elucidated. The aim of this study was to evaluate immunization strategies in a nonhuman primate (NHP) model. Cynomolgus macaques (Macaqua fascicularis) were immunized following different multi-component prime-boost immunization-schedules and subsequently challenged with C. trachomatis SvD in the lower genital tract. The immunization antigens included the recombinant protein antigen CTH522 adjuvanted with CAF01 or aluminium hydroxide, MOMP DNA antigen and MOMP vector antigens (HuAd5 MOMP and MVA MOMP). All antigen constructs were highly immunogenic raising significant systemic C. trachomatis-specific IgG responses. In particularly the CTH522 protein vaccinated groups raised a fast and strong pecificsIgG in serum. The mapping of specific B cell epitopes within the MOMP showed that all vaccinated groups, recognized epitopes near or within the variable domains (VD) of MOMP, with a consistent VD4 response in all animals. Furthermore, serum from all vaccinated groups were able to in vitro neutralize both SvD, SvE and SvF. Antibody responses were reflected on the vaginal and ocular mucosa, which showed detectable levels of IgG. Vaccines also induced C. trachomatis-specific cell mediated responses, as shown by in vitro stimulation and intracellular cytokine staining of peripheral blood mononuclear cells (PBMCs). In general, the protein (CTH522) vaccinated groups established a multifunctional CD4 T cell response, whereas the DNA and Vector vaccinated groups also established a CD8 T cells response. Following vaginal challenge with C. trachomatis SvD, several of the vaccinated groups showed accelerated clearance of the infection, but especially the DNA group, boosted with CAF01 adjuvanted CTH522 to achieve a balanced CD4/CD8 T cell response combined with an IgG response, showed accelerated clearance of the infection.

Chlamydia trachomatis vaccine development - a view on the current challenges and how to move forward

INTRODUCTION

Chlamydia trachomatis is the most common sexually transmitted bacterial pathogen in the world. A licensed vaccine is not yet available, but the first vaccines have entered clinical trials.

AREAS COVERED

: We describe the progress that has been made in our understanding of the type of immunity that a protective vaccine should induce, and the challenges that vaccine developers face. We also focus on the clinical development of a chlamydia vaccine. The first chlamydia vaccine candidate has now been tested in a clinical phase-I trial, and another phase-I trial is currently running. We discuss what it will take to continue this development and what future trial setups could look like.

EXPERT OPINION

The chlamydia field is coming of age and the first phase I clinical trial of a C. trachomatis vaccine has been successfully completed. We expect and hope that this will motivate various stakeholders to support further development of chlamydia vaccines in humans.

Combining Cellular Immunology With RNAseq to Identify Novel Chlamydia T-Cell Subset Signatures

Chlamydia trachomatis serovars A-L cause important diseases of the eyes and reproductive tract by infecting epithelium lining those organs. A major hurdle for vaccine trials is finding a surrogate biomarker for protective immunity. Investigational data argues for T-cell biomarker(s) reflecting mucosal adaption, cytokine polarization, B-cell help, antibacterial effector mechanisms, or some combination thereof. A human investigation and 2 mouse studies link IL-13 to protection from infection/immunopathology. We performed RNAseq on T cells resident in spleens and genital tracts of naturally immune mice. CD4 signatures were consistent with helper function that differed by site including a genital tract-specific Fgl2 signal. The genital tract CD8 signature featured IL-10 and promotion of healing/scarring with a unique transcription of granzyme A. The RNAseq data was used to refine previously published CD4γ13 and CD8γ13 transcriptomes derived from protective T-cell clones, potentially identifying practicable T-cell subset signatures for assessing Chlamydia vaccine candidates.

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.

Insights Into Host Cell Cytokines in Chlamydia Infection

Chlamydial infection causes a number of clinically relevant diseases and induces significant morbidity in humans. Immune and inflammatory responses contribute to both the clearance of Chlamydia infection and pathology in host tissues. Chlamydia infection stimulates host cells to produce a large number of cytokines that trigger and regulate host immune responses against Chlamydia. However, inappropriate responses can occur with excessive production of cytokines, resulting in overreactive inflammatory responses and alterations in host or Chlamydia metabolism. As a result, Chlamydia persists and causes wound healing delays, leading to more severe tissue damage and triggering long-lasting fibrotic sequelae. Here, we summarize the roles of cytokines in Chlamydia infection and pathogenesis, thus advancing our understanding chlamydial infection biology and the pathogenic mechanisms involved.

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.

Chlamydia trachomatis vaccines for genital infections: where are we and how far is there to go?

INTRODUCTION

Chlamydia trachomatis is the most common sexually transmitted bacterial pathogen in the world. Antibiotic treatment does not prevent against reinfection and a vaccine is not yet available.

AREAS COVERED

We focus the review on the progress made of our understanding of the immunological responses required for a vaccine to elicit protection, and on the antigens, adjuvants, routes of immunization and delivery systems that have been tested in animal models. PubMed and Google Scholar were used to search publication on these topics for the last 5 years and recent Reviews were examined.

EXPERT OPINION

The first Phase 1 clinical trial of a C. trachomatis vaccine to protect against genital infections was successfully completed. We expect that, in the next five years, additional vaccine clinical trials will be implemented.

A Class II-Restricted CD8γ13 T-Cell Clone Protects During Chlamydia muridarum Genital Tract Infection

BACKGROUND

The T-cell response to chlamydia genital tract infections in humans and mice is unusual because the majority of antigen-specific CD8 T cells are not class I restricted (referred to here as "unrestricted" or "atypical"). We previously reported that a subset of unrestricted murine chlamydia-specific CD8 T cells had a cytokine polarization pattern that included interferon (IFN)-γ and interleukin (IL)-13.

METHODS

In this study, we investigated the transcriptome of CD8γ13 T cells, comparing them to Tc1 clones using microarray analysis. That study revealed that CD8γ13 polarization included IL-5 in addition to IFN-γ and IL-13. Adoptive transfer studies were performed with Tc1 clones and a CD8γ13 T-cell clone to determine whether either influenced bacterial clearance or immunopathology during Chlamydia muridarum genital tract infections.

RESULTS

To our surprise, an adoptively transferred CD8γ13 T-cell clone was remarkably proficient at preventing chlamydia immunopathology, whereas the multifunctional Tc1 clone did not enhance clearance or significantly alter immunopathology. Mapping studies with major histocompatibility complex (MHC) class I- and class II-deficient splenocytes showed our previously published chlamydia-specific CD8 T-cell clones are MHC class II restricted.

CONCLUSIONS

The MHC class II-restricted CD8 T cells may play an important role in protection from intracellular pathogens that limit class I antigen presentation or diminish CD4 T-cell numbers or impair their function.

Differential miRNA Profiles Correlate With Disparate Immunity Outcomes Associated With Vaccine Immunization and Chlamydial Infection

Vaccine-induced immune responses following immunization with promising Chlamydia vaccines protected experimental animals from Chlamydia-induced upper genital tract pathologies and infertility. In contrast, primary genital infection with live Chlamydia does not protect against these pathologies. We hypothesized that differential miRNA profiles induced in the upper genital tracts (UGT) of mice correlate with the disparate immunity vs. pathologic outcomes associated with vaccine immunization and chlamydial infection. Thus, miRNA expression profiles in the UGT of mice after Chlamydia infection (Live EB) and immunization with dendritic cell (DC)-based vaccine (DC vaccine) or VCG-based vaccine (VCG vaccine) were compared using the NanoString nCounter Mouse miRNA assay. Of the 602 miRNAs differentially expressed (DE) in the UGT of immunized and infected mice, we selected 58 with counts >100 and p-values < 0.05 for further analysis. Interestingly, vaccine immunization and Chlamydia infection induced the expression of distinct miRNA profiles with a higher proportion in vaccine-immunized compared to Chlamydia infected mice; DC vaccine (41), VCG vaccine (23), and Live EB (15). Hierarchical clustering analysis showed notable differences in the uniquely DE miRNAs for each experimental group, with DC vaccine showing the highest number (21 up-regulated, five down-regulated), VCG vaccine (two up-regulated, five down-regulated), and live EB (two up-regulated, four down-regulated). The DC vaccine-immunized group showed the highest number (21 up-regulated and five down-regulated compared to two up-regulated and four down-regulated in the live Chlamydia infected group). Pathway analysis showed that the DE miRNAs target genes that regulate several biological processes and functions associated with immune response and inflammation. These results suggest that the induction of differential miRNA expression plays a significant role in the disparate immunity outcomes associated with Chlamydia infection and vaccination.

Modulation of T helper 1 and T helper 2 immune balance in a murine stress model during Chlamydia muridarum genital infection

A murine model to study the effect of cold-induced stress (CIS) on Chlamydia muridarum genital infection and immune response has been developed in our laboratory. Previous results in the lab show that CIS increases the intensity of chlamydia genital infection, but little is known about the effects and mechanisms of CIS on the differentiation and activities of CD4+ T cell subpopulations and bone marrow-derived dendritic cells (BMDCs). The factors that regulate the production of T helper 1 (Th1) or T helper 2 (Th2) cytokines are not well defined. In this study, we examined whether CIS modulates the expressions of beta-adrenergic receptor (β-AR), transcription factors, hallmark cytokines of Th1 and Th2, and differentiation of BMDCs during C. muridarum genital infection in the murine model. Our results show that the mRNA level of the beta2-adrenergic receptor (β2-AR) compared to β1-AR and β3-AR was high in the mixed populations of CD4+ T cells and BMDCs. Furthermore, we observed decreased expression of T-bet, low level of Interferon-gamma (IFN-γ) production, increased expression of GATA-3, and Interleukin-4 (IL-4) production in CD4+ T cells of stressed mice. Exposure of BMDCs to Fenoterol, β2-AR agonist, or ICI118,551, β2-AR antagonist, revealed significant β2-AR stimulation or inhibition, respectively, in stressed mice. Moreover, co-culturing of mature BMDCs and naïve CD4+ T cells increased the production of IL-4, IL-10, L-17, and IL-23 cytokines, suggesting that stimulation of β2-AR leads to the increased production of Th2 cytokines. Overall, our results show for the first time that CIS promotes the switching from a Th1 to Th2 cytokine environment. This was evidenced in the murine stress model by the overexpression of GATA-3 concurrent with elevated IL-4 production, reduced T-bet expression, and IFN-γ secretion.

Mathematical modelling of the role of mucosal vaccine on the within-host dynamics of Chlamydia trachomatis

A mathematical model of the within-host replicative dynamics of C. trachomatis infection and its interactions with the immune system, in the presence of a mucosal vaccine, is presented. Our aim is to estimate the requisite efficacy of an efficacious mucosal vaccine that could promote a stable disease-free state in vivo. Sensitivity analysis was used to quantify how variability in the model parameters influence the value of the disease threshold R₀. This shows that the two most important factors to be considered for achieving a disease-free state state in vivo, based on their influence on R₀, are the efficacy of the Chlamydia vaccine, and the rate at which the humoral immune response protects healthy epithelial cells from infection. Numerical simulations of the model show that a vaccine with a minimum efficacy of 86% may be required for the in vivo control of Chlamydia burden. Such effective but imperfect Chlamydia vaccine could confer long-term protective immunity to genital Chlamydia infections. Conditions under which lower vaccine efficacies may suffice are also explored.

Epidermal Growth Factor Receptor and Transforming Growth Factor β Signaling Pathways Cooperate To Mediate Chlamydia Pathogenesis

Human genital Chlamydia infection is a major public health concern due to the serious reproductive system complications. Chlamydia binds several receptor tyrosine kinases (RTKs) on host cells, including the epidermal growth factor receptor (EGFR), and activates cellular signaling cascades for host invasion, cytoskeletal remodeling, optimal inclusion development, and induction of pathogenic epithelial-mesenchyme transition (EMT). Chlamydia also upregulates transforming growth factor beta (TGF-β) expression, whose signaling pathway synergizes with the EGFR cascade, but its role in infectivity, inclusions, and EMT induction is unknown. We hypothesized that the EGFR and TGF-β signaling pathways cooperate during chlamydial infection for optimal inclusion development and stable EMT induction. The results revealed that Chlamydia upregulated TGF-β expression as early as 6 h postinfection of epithelial cells and stimulated both the EGFR and TGF-β signaling pathways. Inhibition of either the EGFR or TGF-βR1 signaling substantially reduced inclusion development; however, the combined inhibition of both EGFR and TGF-βR1 signaling reduced inclusions by over 90% and prevented EMT induction. Importantly, EGFR inhibition suppressed TGF-β expression, and an inhibitory thrombospondin-1 (Tsp1)-based peptide inhibited chlamydia-induced EMT, revealing a major source of active TGF-β during infection. Finally, TGF-βR signaling inhibition suppressed the expression of transforming acidic coiled-coil protein-3 (TACC3), which stabilizes EGFR signaling, suggesting reciprocal regulation between TGF-β and EGFR signaling during chlamydial infection. Thus, RTK-mediated host invasion by chlamydia upregulated TGF-β expression and signaling, which cooperated with other cellular signaling cascades and cytoskeletal remodeling to support optimal inclusion development and EMT induction. This finding may provide new targets for chlamydial disease biomarkers and prevention.

Effect of Time of Day of Infection on Chlamydia Infectivity and Pathogenesis

Genital chlamydia infection in women causes complications such as pelvic inflammatory disease and tubal factor infertility, but it is unclear why some women are more susceptible than others. Possible factors, such as time of day of chlamydia infection on chlamydial pathogenesis has not been determined. We hypothesised that infections during the day, will cause increased complications compared to infections at night. Mice placed under normal 12:12 light: dark (LD) cycle were infected intravaginally with Chlamydia muridarum either at zeitgeber time 3, ZT3 and ZT15. Infectivity was monitored by periodic vaginal swabs and chlamydiae isolation. Blood and vaginal washes were collected for host immunologic response assessments. The reproductive tracts of the mice were examined histopathologically, and fertility was determined by embryo enumeration after mating. Mice infected at ZT3 shed significantly more C. muridarum than mice infected at ZT15. This correlated with the increased genital tract pathology observed in mice infected at ZT3. Mice infected at ZT3 were less fertile than mice infected at ZT15. The results suggest that the time of day of infection influences chlamydial pathogenesis, it indicates a possible association between complications from chlamydia infection and host circadian clock, which may lead to a better understanding of chlamydial pathogenesis.

A unique insight into the MiRNA profile during genital chlamydial infection

Background

Genital C. trachomatis infection may cause pelvic inflammatory disease (PID) that can lead to tubal factor infertility (TFI). Understanding the pathogenesis of chlamydial complications including the pathophysiological processes within the female host genital tract is important in preventing adverse pathology. MicroRNAs regulate several pathophysiological processes of infectious and non-infectious etiologies. In this study, we tested the hypothesis that the miRNA profile of single and repeat genital chlamydial infections will be different and that these differences will be time dependent. Thus, we analyzed and compared differentially expressed mice genital tract miRNAs after single and repeat chlamydia infections using a C. muridarum mouse model. Mice were sacrificed and their genital tract tissues were collected at 1, 2, 4, and 8 weeks after a single and repeat chlamydia infections. Histopathology, and miRNA sequencing were performed.

Results

Histopathology presentation showed that the oviduct and uterus of reinfected mice were more inflamed, distended and dilated compared to mice infected once. The miRNAs expression profile was different in the reproductive tissues after a reinfection, with a greater number of miRNAs expressed after reinfection. Also, the number of miRNAs expressed each week after chlamydia infection and reinfection varied, with weeks eight and one having the highest number of differentially expressed miRNAs for chlamydia infection and reinfection respectively. Ten miRNAs; mmu-miR-378b, mmu-miR-204-5p, mmu-miR-151-5p, mmu-miR-142-3p, mmu-miR-128-3p, mmu-miR-335-3p, mmu-miR-195a-3p, mmu-miR-142-5p, mmu-miR-106a-5p and mmu-miR-92a-3p were common in both primary chlamydia infection and reinfection. Pathway analysis showed that, amongst other functions, the differentially regulated miRNAs control pathways involved in cellular and tissue development, disease conditions and toxicity.

Conclusions

This study provides insights into the changes in miRNA expression over time after chlamydia infection and reinfection, as well as the pathways they regulate to determine pathological outcomes. The miRNAs networks generated in our study shows that there are differences in the focus molecules involved in significant biological functions in chlamydia infection and reinfection, implying that chlamydial pathogenesis occurs differently for each type of infection and that this could be important when determining treatments regime and disease outcome. The study underscores the crucial role of host factors in chlamydia pathogenesis.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5495-6) contains supplementary material, which is available to authorized users.

The molecular mechanism of induction of unfolded protein response by Chlamydia

The unfolded protein response (UPR) contributes to chlamydial pathogenesis, as a source of lipids and ATP during replication, and for establishing the initial anti-apoptotic state of host cell that ensures successful inclusion development. The molecular mechanism(s) of UPR induction by Chlamydia is unknown. Chlamydia use type III secretion system (T3SS) effector proteins (e.g, the Translocated Actin-Recruiting Phosphoprotein (Tarp) to stimulate host cell's cytoskeletal reorganization that facilitates invasion and inclusion development. We investigated the hypothesis that T3SS effector-mediated assembly of myosin-II complex produces activated non-muscle myosin heavy chain II (NMMHC-II), which then binds the UPR master regulator (BiP) and/or transducers to induce UPR. Our results revealed the interaction of the chlamydial effector proteins (CT228 and Tarp) with components of the myosin II complex and UPR regulator and transducer during infection. These interactions caused the activation and binding of NMMHC-II to BiP and IRE1α leading to UPR induction. In addition, specific inhibitors of myosin light chain kinase, Tarp oligomerization and myosin ATPase significantly reduced UPR activation and Chlamydia replication. Thus, Chlamydia induce UPR through T3SS effector-mediated activation of NMMHC-II components of the myosin complex to facilitate infectivity. The finding provides greater insights into chlamydial pathogenesis with the potential to identify therapeutic targets and formulations.

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.

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.

Molecular Pathogenesis of Chlamydia Disease Complications: Epithelial-Mesenchymal Transition and Fibrosis

The reproductive system complications of genital chlamydial infection include fallopian tube fibrosis and tubal factor infertility. However, the molecular pathogenesis of these complications remains poorly understood. The induction of pathogenic epithelial-mesenchymal transition (EMT) through microRNA (miRNA) dysregulation was recently proposed as the pathogenic basis of chlamydial complications. Focusing on fibrogenesis, we investigated the hypothesis that chlamydia-induced fibrosis is caused by EMT-driven generation of myofibroblasts, the effector cells of fibrosis that produce excessive extracellular matrix (ECM) proteins. The results revealed that the targets of a major category of altered miRNAs during chlamydial infection are key components of the pathophysiological process of fibrogenesis; these target molecules include collagen types I, III, and IV, transforming growth factor β (TGF-β), TGF-β receptor 1 (TGF-βR1), connective tissue growth factor (CTGF), E-cadherin, SRY-box 7 (SOX7), and NFAT (nuclear factor of activated T cells) kinase dual-specificity tyrosine (Y) phosphorylation-regulated kinase 1a (Dyrk1a). Chlamydial induction of EMT resulted in the generation of α-smooth muscle actin (α-SMA)-positive myofibroblasts that produced ECM proteins, including collagen types I and III and fibronectin. Furthermore, the inhibition of EMT prevented the generation of myofibroblasts and production of ECM proteins during chlamydial infection. These findings may provide useful avenues for targeting EMT or specific components of the EMT pathways as a therapeutic intervention strategy to prevent chlamydia-related complications.

Expression of CXCR3 on Adaptive and Innate Immune Cells Contributes Oviduct Pathology throughout Chlamydia muridarum Infection

CXCR3 is a chemokine receptor expressed on a wide range of leukocytes, and it is involved in leukocyte migration throughout the blood and lymphatics. Specifically, CXCR3 is required for lymphocyte homing to the genital mucosa. When compared to wild type (WT) mice, CXCR3 deficiency (CXCR3-/-) mice infected with Chlamydia muridarum (C. muridarum) did not display impaired clearance and resolution of infection. However, they possessed significantly higher bacterial burden and lower levels of IFN-γ-producing TH1 cells. The knockouts also demonstrated a significant decrease in the level of activated conventional dendritic cells in the GT, ultimately leading to the decrease in activated TH1 cells. In addition, few activated plasmacytoid dendritic cells, which possess an inflammatory phenotype, were found in the lymph node of infected mice. This reduction in pDCs may be responsible for the decrease in neutrophils, which are acute inflammatory cells, in the CXCR3-/- mice. Due to the significantly reduced level of acute inflammation, these mice also possess a decrease in dilation and pathology in the oviduct. This demonstrates that the CXCR3-/- mice possess the ability to clear C. muridarum infections, but they do so without the increased inflammation and pathology in the GT.

Effect of cold water-induced stress on immune response, pathology and fertility in mice during Chlamydia muridarum genital infection

Genital infection by Chlamydia trachomatis is the most common bacterial sexually transmitted disease worldwide. It causes serious reproductive health complications, including pelvic inflammatory disease and infertility. Stress is implicated as a risk factor for various infections; however, its effect on chlamydia genital infection is unknown. We previously showed that repeated exposure of mice to cold water results in increased severity of chlamydia genital infection. In this study, cold water-induced stress resulted in (i) elevated levels of norepinephrine (NE) and epinephrine in the spleen and genital tract of stressed mice; (ii) elevated IL-1β, TNF-α, IL-6 and nitric oxide production in macrophage-rich peritoneal cells of mice; (iii) supplement of NE in vitro exerts an immunosuppressive effect on splenic T-cell production of cytokines; (iv) decreased C. muridarum shedding in the genital tract of β1Adr/β2Adr receptor KO mice; and (v) a higher rate of infertility in infected mice. These results suggest that cold water stress induces the production of catecholamines, which may play a critical role in the modulation of the immune system leading to increased intensity of C. muridarum genital infection.

The Roles of Unfolded Protein Response Pathways in Chlamydia Pathogenesis

Chlamydia is an obligate intracellular bacterium that relies on host cells for essential nutrients and adenosine triphosphate (ATP) for a productive infection. Although the unfolded protein response (UPR) plays a major role in certain microbial infectivity, its role in chlamydial pathogenesis is unknown. We hypothesized that Chlamydia induces UPR and exploits it to upregulate host cell uptake and metabolism of glucose, production of ATP, phospholipids, and other molecules required for its replicative development and host survival. Using a combination of biochemical and pathway inhibition assays, we showed that the 3 UPR pathway transducers-protein kinase RNA-activated (PKR)-like ER kinase (PERK), inositol-requiring enzyme-1α (IRE1α), and activating transcription factor-6α (ATF6α)-were activated during Chlamydia infection. The kinase activity of PERK and ribonuclease (RNase) of IRE1α mediated the upregulation of hexokinase II and production of ATP via substrate-level phosphorylation. In addition, the activation of PERK and IRE1α promoted autophagy formation and apoptosis resistance for host survival. Moreover, the activation of IRE1α resulted in the generation of spliced X-box binding protein 1 (sXBP1) and upregulation of lipid production. The vital role of UPR pathways in Chlamydia development and pathogenesis could lead to the identification of potential molecular targets for therapeutics against Chlamydia.

Rectal administration of a chlamydial subunit vaccine protects against genital infection and upper reproductive tract pathology in mice

In this study, we tested the hypothesis that rectal immunization with a VCG-based chlamydial vaccine would cross-protect mice against heterologous genital Chlamydia trachomatis infection and Chlamydia-induced upper genital tract pathologies in mice. Female mice were immunized with a C. trachomatis serovar D-derived subunit vaccine or control or live serovar D elementary bodies (EBs) and the antigen-specific mucosal and systemic immune responses were characterized. Vaccine efficacy was determined by evaluating the intensity and duration of genital chlamydial shedding following intravaginal challenge with live serovar E chlamydiae. Protection against upper genital tract pathology was determined by assessing infertility and tubal inflammation. Rectal immunization elicited high levels of chlamydial-specific IFN-gamma-producing CD4 T cells and humoral immune responses in mucosal and systemic tissues. The elicited immune effectors cross-reacted with the serovar E chlamydial antigen and reduced the length and intensity of genital chlamydial shedding. Furthermore, immunization with the VCG-vaccine but not the rVCG-gD2 control reduced the incidence of tubal inflammation and protected mice against Chlamydia-induced infertility. These results highlight the potential of rectal immunization as a viable mucosal route for inducing protective immunity in the female genital tract.

The Chlamydia-Secreted Protease CPAF Promotes Chlamydial Survival in the Mouse Lower Genital Tract

Despite the extensive in vitro characterization of CPAF (chlamydial protease/proteasome-like activity factor), its role in chlamydial infection and pathogenesis remains unclear. We now report that a Chlamydia trachomatis strain deficient in expression of CPAF (L2-17) is no longer able to establish a successful infection in the mouse lower genital tract following an intravaginal inoculation. The L2-17 organisms were cleared from the mouse lower genital tract within a few days, while a CPAF-sufficient C. trachomatis strain (L2-5) survived in the lower genital tract for more than 3 weeks. However, both the L2-17 and L2-5 organisms maintained robust infection courses that lasted up to 4 weeks when they were directly delivered into the mouse upper genital tract. The CPAF-dependent chlamydial survival in the lower genital tract was confirmed in multiple strains of mice. Thus, we have demonstrated a critical role of CPAF in promoting C. trachomatis survival in the mouse lower genital tracts. It will be interesting to further investigate the mechanisms of the CPAF-dependent chlamydial pathogenicity.

Immunity, immunopathology, and human vaccine development against sexually transmitted Chlamydia trachomatis

This review examines the immunity, immunopathology, and contemporary problems of vaccine development against sexually transmitted Chlamydia trachomatis. Despite improved surveillance and treatment initiatives, the incidence of C. trachomatis infection has increased dramatically over the past 30 years in both the developed and developing world. Studies in animal models have shown that protective immunity to C. trachomatis is largely mediated by Th1 T cells producing IFN-γ which is needed to prevent dissemination of infection. Similar protection appears to develop in humans but in contrast to mice, immunity in humans may take years to develop. Animal studies and evidence from human infection indicate that immunity to C. trachomatis is accompanied by significant pathology in the upper genital tract. Although no credible evidence is currently available to indicate that autoimmunity plays a role, nevertheless, this underscores the necessity to design vaccines strictly based on chlamydial-specific antigens and to avoid those displaying even minimal sequence homologies with host molecules. Current advances in C. trachomatis vaccine development as well as alternatives for designing new vaccines for this disease are discussed. A novel approach for chlamydia vaccine development, based on targeting endogenous dendritic cells, is described.

Subunit vaccines for the prevention of mucosal infection with Chlamydia trachomatis

Chlamydia trachomatis is the most common preventable cause of tubal infertility in women. In high-income countries, despite public health control efforts, C. trachomatis case rates continue to rise. Most medium and low-income countries lack any Chlamydia control program; therefore, a vaccine is essential for the control of Chlamydia infections. A rationally designed Chlamydia vaccine requires understanding of the immunological correlates of protective immunity, pathological responses to this mucosal pathogen, identification of optimal vaccine antigens and selection of suitable adjuvant delivery systems that engender protective immunity. Fortunately, Chlamydia vaccinology is facilitated by genomic knowledge and by murine models that reproduce many of the features of human C. trachomatis infection. This article reviews recent progress in these areas with a focus on subunit vaccine development.

Immunopathogenesis of Chlamydial Infections

Chlamydial infections lead to a number of clinically relevant diseases and induce significant morbidity in human populations. It is generally understood that certain components of the host immune response to infection also mediate such disease pathologies. A clear understanding of pathogenic mechanisms will enable us to devise better preventive and/or intervention strategies to mitigate the morbidity caused by these infections. Over the years, numerous studies have been conducted to explore the immunopathogenic mechanisms of Chlamydia-induced diseases of the eye, reproductive tract, respiratory tract, and cardiovascular systems. In this article, we provide an overview of the diseases caused by Chlamydia, animal models used to study disease pathology, and a historical context to the efforts to understand chlamydial pathogenesis. Furthermore, we discuss recent findings regarding pathogenesis, with an emphasis on the role of the adaptive immune response in the development of chlamydial disease sequelae. Finally, we summarize the key insights obtained from studies of chlamydial pathogenesis and avenues that remain to be explored in order to inform the next steps of vaccine development against chlamydial infections.

Role of Epithelial-Mesenchyme Transition in Chlamydia Pathogenesis

Chlamydia trachomatis genital infection in women causes serious adverse reproductive complications, and is a strong co-factor for human papilloma virus (HPV)-associated cervical epithelial carcinoma. We tested the hypothesis that Chlamydia induces epithelial-mesenchyme transition (EMT) involving T cell-derived TNF-alpha signaling, caspase activation, cleavage inactivation of dicer and dysregulation of micro-RNA (miRNA) in the reproductive epithelium; the pathologic process of EMT causes fibrosis and fertility-related epithelial dysfunction, and also provides the co-factor function for HPV-related cervical epithelial carcinoma. Using a combination of microarrays, immunohistochemistry and proteomics, we showed that chlamydia altered the expression of crucial miRNAs that control EMT, fibrosis and tumorigenesis; specifically, miR-15a, miR-29b, miR-382 and MiR-429 that maintain epithelial integrity were down-regulated, while miR-9, mi-R-19a, miR-22 and miR-205 that promote EMT, fibrosis and tumorigenesis were up-regulated. Chlamydia induced EMT in vitro and in vivo, marked by the suppression of normal epithelial cell markers especially E-cadherin but up-regulation of mesenchymal markers of pathological EMT, including T-cadherin, MMP9, and fibronectin. Also, Chlamydia upregulated pro-EMT regulators, including the zinc finger E-box binding homeobox protein, ZEB1, Snail1/2, and thrombospondin1 (Thbs1), but down-regulated anti-EMT and fertility promoting proteins (i.e., the major gap junction protein connexin 43 (Cx43), Mets1, Add1Scarb1 and MARCKSL1). T cell-derived TNF-alpha signaling was required for chlamydial-induced infertility and caspase inhibitors prevented both infertility and EMT. Thus, chlamydial-induced T cell-derived TNF-alpha activated caspases that inactivated dicer, causing alteration in the expression of reproductive epithelial miRNAs and induction of EMT. EMT causes epithelial malfunction, fibrosis, infertility, and the enhancement of tumorigenesis of HPV oncogene-transformed epithelial cells. These findings provide a novel understanding of the molecular pathogenesis of chlamydia-associated diseases, which may guide a rational prevention strategy.

Potential protective effect of a G>A SNP in the 3'UTR of HLA-A for Chlamydia trachomatis symptomatology and severity of infection

The interindividual differences in response to Chlamydia trachomatis (CT) infections are for an important part based on the differences in our host genetic make-up. In the past, several genes and pathways have been identified and linked to protection against or risk for CT infection (i.e. susceptibility), and/or the severity of infection, with a major emphasis on the development of tubal pathology, one of the main causes of female infertility. In the current study, we analyzed in Dutch Caucasian women whether the carriage of HLA-A G>A SNP (rs1655900) was related to the susceptibility of CT infection in a STD cohort (n = 329) and to the severity of infection in a subfertility cohort (n = 482). We also investigated if this A-allele was linked to increase in severity of symptoms, from mild symptoms (lower genital infection) to lower abdominal pain (upper genital tract infection) to the most severe late complication of tubal pathology, including double-sided tubal pathology. We showed that the carriage of HLA-A SNP rs1655900 studied is not associated with the susceptibility to CT infection based on the data from the STD cohort, but might be protective to the development of late complications (p = 0.0349), especially tubal pathology could be relevant.

Evolution of hosts paying manifold costs of defence

Hosts are expected to incur several physiological costs in defending against parasites. These include constitutive energetic (or other resource) costs of a defence system, facultative resource costs of deploying defences when parasites strike, and immunopathological costs of collateral damage. Here, we investigate the evolution of host recovery rates, varying the source and magnitude of immune costs. In line with previous work, we find that hosts paying facultative resource costs evolve faster recovery rates than hosts paying constitutive costs. However, recovery rate is more sensitive to changes in facultative costs, potentially explaining why constitutive costs are hard to detect empirically. Moreover, we find that immunopathology costs which increase with recovery rate can erode the benefits of defence, promoting chronicity of infection. Immunopathology can also lead to hosts evolving low recovery rate in response to virulent parasites. Furthermore, when immunopathology reduces fecundity as recovery rate increases (e.g. as for T-cell responses to urogenital chlamydiosis), then recovery and reproductive rates do not covary as predicted in eco-immunology. These results suggest that immunopathological and resource costs have qualitatively different effects on host evolution and that embracing the complexity of immune costs may be essential for explaining variability in immune defence in nature.

Interleukin-10 modulates antigen presentation by dendritic cells through regulation of NLRP3 inflammasome assembly during Chlamydia infection

Interleukin-10 (IL-10) has been implicated in susceptibility to genital chlamydial infection and the development of tubal pathologies. IL-10 limitation also resulted in the rapid elicitation of immune responses against Chlamydia, and decreased levels of IL-10 correlated with protective anti-Chlamydia immunity. To investigate the molecular basis for these effects, we compared the reproductive pathologies and fertility rates in Chlamydia-infected wild-type (WT) and IL-10-knockout (IL-10(-/-)) mice; we also analyzed the expression of the Toll-like receptor (TLR)/interleukin-1 receptor (IL-1R) superfamily, IL-1β production, NLRP3 inflammasome assembly and activation, and the immunostimulatory capacity and apoptotic predilection of Chlamydia-exposed dendritic cells (DCs) from WT and IL-10(-/-) mice. Our results revealed that, in addition to the rapid clearance of infection, genitally infected IL-10(-/-) mice were protected from tubal pathologies and infertility, whereas WT (IL-10(+/+)) mice were not. Chlamydia-pulsed IL-10(-/-) DCs expressed larger numbers of TLR4/IL-1R molecules and had enhanced IL-1β production. In addition, NLRP3 inflammasome assembly was suppressed in IL-10(-/-) DCs through the inhibition of the P2X purinoceptor 7 (P2X7) receptor (P2X7R), an ATP-gated ion channel, and a decrease in intracellular Ca(2+) levels, which inhibited DC apoptosis. Thus, the potent immunostimulatory capacity of IL-10-deficient DCs is due, at least in part, to the suppression of the intracellular inflammasome assembly, which prevents DC apoptosis, allowing efficient antigen presentation. The results indicate that IL-10 deficiency enables efficient antigen presentation by DCs for rapid and enhanced immune activation against Chlamydia, which results in rapid microbial clearance, which prevents tubal pathologies during infection. Our finding has important implications for the induction of protective immunity against Chlamydia and other infectious and noninfectious diseases by vaccines.

The contribution of Chlamydia-specific CD8⁺ T cells to upper genital tract pathology

Genital chlamydial infections lead to severe upper reproductive tract pathology in a subset of untreated women. We demonstrated previously that TNF-α producing CD8⁺ T cells contribute significantly to chlamydial upper genital tract pathology in female mice. Additionally, we observed minimal chlamydial oviduct pathology develops in OT-1 transgenic (OT-1) mice, wherein CD8⁺ T cell repertoire is restricted to recognition of the ovalbumin peptide Ova_257–264, suggesting that non-Chlamydia-specific CD8⁺ T cells may not be responsible for chlamydial pathogenesis. In the current study, we evaluated whether antigen-specific CD8⁺ T cells mediate chlamydial pathology. Groups of wild type C57BL/6J (WT), OT-1 mice, and OT-1 mice replete with WT CD8⁺ T cells (1×10⁶ cells/mouse intravenously) were infected intravaginally with C. muridarum (5 × 10⁴ IFU/mouse). Serum total anti-Chlamydia antibody and total splenic anti-Chlamydia IFN-γ and TNF-α responses were comparable among the three groups of animals. However, Chlamydia-specific IFN-γ and TNF-α production from purified splenic CD8⁺ T cells of OT-1 mice was minimal, whereas responses in OT-1 mice replete with WT CD8⁺ T cells were comparable to those in WT animals. Vaginal chlamydial clearance was comparable between the three groups of mice. Importantly, the incidence and severity of oviduct and uterine horn pathology was significantly reduced in OT-1 mice but reverted to WT levels in OT-1 mice replete with WT CD8⁺ T cells. Collectively, these results demonstrate that Chlamydia-specific CD8⁺ T cells contribute significantly to upper genital tract pathology.

CD8+ T cells mediate Chlamydia pneumoniae-induced atherosclerosis in mice

Chlamydia pneumoniae is a community-acquired bacterial pathogen that has been strongly associated with exacerbation of atherosclerosis. We evaluated the role of CD8(+) T cells in the C57BL/6J mouse model of C. pneumoniae-induced atherosclerosis. Groups of 4- to 6-week-old male wild-type C57BL/6J (WT) mice and mice with a gene deficiency in CD8α (CD8 KO mice) were infected with C. pneumoniae and fed a high fat (HF) diet. Serum antibody response and serum cholesterol were comparable between infected CD8 KO and WT mice. However, infected CD8 KO mice displayed significantly reduced atherosclerotic plaque lesions on day 100 compared to infected WT mice, at a level comparable to both uninfected WT and CD8 KO mice fed the HF diet. Moreover, repletion of CD8 KO mice with WT CD8(+) T cells (1 × 10(7) cells/mouse intravenously) at the time of infection reverted atherosclerotic plaque lesions to WT levels. These results demonstrate that CD8(+) T cells play an important role in mediating C. pneumoniae-induced exacerbation of atherosclerotic pathology.

Tumor Necrosis Factor (TNF) Receptor Superfamily Member 1b on CD8+ T Cells and TNF Receptor Superfamily Member 1a on Non-CD8+ T Cells Contribute Significantly to Upper Genital Tract Pathology Following Chlamydial Infection

BACKGROUND

We demonstrated previously that tumor necrosis factor α (TNF-α)-producing Chlamydia-specific CD8(+) T cells cause oviduct pathological sequelae.

METHODS

In the current study, we used wild-type C57BL/6J (WT) mice with a deficiency in genes encoding TNF receptor superfamily member 1a (TNFR1; TNFR1 knockout [KO] mice), TNF receptor superfamily member 1b (TNFR2; TNFR2 KO mice), and both TNFR1 and TNFR2 (TNFR1/2 double KO [DKO] mice) and mix-match adoptive transfers of CD8(+) T cells to study chlamydial pathogenesis.

RESULTS

TNFR1 KO, TNFR2 KO, and TNFR1/2 DKO mice displayed comparable clearance of primary or secondary genital Chlamydia muridarum infection but significantly reduced oviduct pathology, compared with WT animals. The Chlamydia-specific total cellular cytokine response in splenic and draining lymph nodes and the antibody response in serum were comparable between the WT and KO animals. However, CD8(+) T cells from TNFR2 KO mice displayed significantly reduced activation (CD11a expression and cytokine production), compared with TNFR1 KO or WT animals. Repletion of TNFR2 KO mice with WT CD8(+) T cells but not with TNFR2 KO CD8(+) T cells and repletion of TNFR1 KO mice with either WT or TNFR1 KO CD8(+) T cells restored oviduct pathology to WT levels in both KO groups.

CONCLUSIONS

Collectively, these results demonstrate that TNFR2-bearing CD8(+) T cells and TNFR1-bearing non-CD8(+) T cells contribute significantly to oviduct pathology following genital chlamydial infection.

An atypical CD8 T-cell response to Chlamydia muridarum genital tract infections includes T cells that produce interleukin-13

Chlamydia trachomatis urogenital serovars D-K are intracellular bacterial pathogens that replicate almost exclusively in human reproductive tract epithelium. In the C. muridarum mouse model for human Chlamydia genital tract infections CD4 T helper type 1 cell responses mediate protective immunity while CD8 T-cell responses have been associated with scarring and infertility. Scarring mediated by CD8 T cells requires production of tumour necrosis factor-α (TNF-α); however, TNF-α is associated with protective immunity mediated by CD4 T cells. The latter result suggests that TNF-α in-and-of itself may not be the sole determining factor in immunopathology. CD8 T cells mediating immunopathology presumably do something in addition to producing TNF-α that is detrimental during resolution of genital tract infections. To investigate the mechanism underlying CD8 immunopathology we attempted to isolate Chlamydia-specific CD8 T-cell clones from mice that self-cleared genital tract infections. They could not be derived with antigen-pulsed irradiated naive splenocytes; instead derivation required use of irradiated immune splenocyte antigen-presenting cells. The Chlamydia-specific CD8 T-cell clones had relatively low cell surface CD8 levels and the majority were not restricted by MHC class Ia molecules. They did not express Plac8, and had varying abilities to terminate Chlamydia replication in epithelial cells. Two of the five CD8 clones produced interleukin-13 (IL-13) in addition to IL-2, TNF-α, IL-10 and interferon-γ. IL-13-producing Chlamydia-specific CD8 T cells may contribute to immunopathology during C. muridarum genital tract infections based on known roles of TNF-α and IL-13 in scar formation.

Perforin is detrimental to controlling [corrected] C. muridarum replication in vitro, but not in vivo

CD4 T cells are critical for clearing experimental Chlamydia muridarum genital tract infections. Two independent in vitro CD4 T cell mechanisms have been identified for terminating Chlamydia replication in epithelial cells. One mechanism, requiring IFN-γ and T cell-epithelial cell contact, terminates infection by triggering epithelial production of nitric oxide to chlamydiacidal levels; the second is dependent on T cell degranulation. We recently demonstrated that there are two independent in vivo clearance mechanisms singly sufficient for clearing genital tract infections within six weeks; one dependent on iNOS, the other on Plac8. Redundant genital tract clearance mechanisms bring into question negative results in single-gene knockout mice. Two groups have shown that perforin-knockout mice were not compromised in their ability to clear C. muridarum genital tract infections. Because cell lysis would be detrimental to epithelial nitric oxide production we hypothesized that perforin was not critical for iNOS-dependent clearance, but posited that perforin could play a role in Plac8-dependent clearance. We tested whether the Plac8-dependent clearance was perforin-dependent by pharmacologically inhibiting iNOS in perforin-knockout mice. In vitro we found that perforin was detrimental to iNOS-dependent CD4 T cell termination of Chlamydia replication in epithelial cells. In vivo, unexpectedly, clearance in perforin knockout mice was delayed to the end of week 7 regardless of iNOS status. The discordant in vitro/in vivo results suggest that the perforin's contribution to bacterial clearance in vivo is not though enhancing CD4 T cell termination of Chlamydia replication in epithelial cells, but likely via a mechanism independent of T cell-epithelial cell interactions.

Beyond "safe sex"--can we fight adolescent pelvic inflammatory disease?

Pelvic inflammatory disease (PID) is a common disorder affecting sexually active adolescents. The Centers for Disease Control and Prevention (CDC) and European CDC report Chlamydia trachomatis as the most common sexually transmitted infection and one of the main etiological agents causing PID. C. trachomatis' and PID's high prevalence may be attributed to multiple factors including high-risk sexual behaviors, sensitive laboratory diagnostics (polymerase chain reaction), and the introduction of chlamydia screening programs. The pathogenesis of C. trachomatis infection is complex with recent data highlighting the role of toll-like receptor 2 and four in the mediation of the inflammatory cascade. The authors review the etiology of the disease, explore its pathogenesis, and discuss a variety of strategies that may be implemented to reduce the prevalence of C. trachomatis including: (a) behavioral risk reduction, (b) effective screening of asymptomatic females, (c) targeted male screening, (d) implementation of a sensitive, rapid, self-administered point-of-care testing, and (e) development of an effective vaccine.

Chlamydia trachomatis control requires a vaccine

As the most common reported communicable disease in North America and Europe, Chlamydia trachomatis is the focus of concerted public health control efforts based on screening and treatment. Unexpectedly control efforts are accompanied by rising reinfection rates attributed in part to arresting the development of herd immunity. Shortening the duration of infection through the testing and treatment program is the root cause behind the arrested immunity hypothesis and because of this a vaccine will be essential to control efforts. Advances in Chlamydia vaccinomics have revealed the C. trachomatis antigens that can be used to constitute a subunit vaccine and a vaccine solution appears to be scientifically achievable. We propose that an accelerated C. trachomatis vaccine effort requires coordinated partnership among academic, public health and private sector players together with a commitment to C. trachomatis vaccine control as a global public health priority.

Chlamydophila pneumoniae in human immortal Jurkat cells and primary lymphocytes uncontrolled by interferon-γ

Lymphocytes are a potential host cell for Chlamydophila pneumoniae, although why the bacteria must hide in lymphocytes remains unknown. Meanwhile, interferon (IFN)-γ is a crucial factor for eliminating chlamydiae from infected cells through indoleamine 2,3-dioxygenase (IDO) expression, resulting in depletion of tryptophan. We therefore assessed if lymphocytes could work as a shelter for the bacteria to escape IFN-γ. C. pneumoniae grew normally in human lymphoid Jurkat cells, even in the presence of IFN-γ or under stimulation with phorbol myristate acetate plus ionomycin. Although Jurkat cells expressed IFN-γ receptor CD119, their lack of IDO expression was confirmed by RT-PCR and western blotting. Also, C. pneumoniae survived in enriched human peripheral blood lymphocytes, even in the presence of IFN-γ. Furthermore, C. pneumoniae in spleen cells obtained from IFN-γ knockout mice with C57BL/6 background was maintained in a similar way to wild-type mice, supporting a minimal role of IFN-γ-related response for eliminating C. pneumoniae from lymphocytes. Thus, we concluded that IFN-γ did not remove C. pneumoniae from lymphocytes, possibly providing a shelter for C. pneumoniae to escape from the innate immune response, which has direct clinical significance.

Prevention of Chlamydia-induced infertility by inhibition of local caspase activity

Tubal factor infertility (TFI) represents 36% of female infertility and genital infection by Chlamydia trachomatis (C. trachomatis) is a major cause. Although TFI is associated with host inflammatory responses to bacterial components, the molecular pathogenesis of Chlamydia-induced infertility remains poorly understood. We investigated the hypothesis that activation of specific cysteine proteases, the caspases, during C. trachomatis genital infection causes the disruption of key fertility-promoting molecules required for embryo development and implantation. We analyzed the effect of caspase inhibition on infertility and the integrity of Dicer, a caspase-sensitive, fertility-promoting ribonuclease III enzyme, and key micro-RNAs in the reproductive system. Genital infection with the inflammation- and caspase-inducing, wild-type C. trachomatis serovar L2 led to infertility, but the noninflammation-inducing, plasmid-free strain did not. We confirmed that caspase-mediated apoptotic tissue destruction may contribute to chlamydial pathogenesis. Caspase-1 or -3 deficiency, or local administration of the pan caspase inhibitor, Z-VAD-FMK into normal mice protected against Chlamydia-induced infertility. Finally, the oviducts of infected infertile mice showed evidence of caspase-mediated cleavage inactivation of Dicer and alteration in critical miRNAs that regulate growth, differentiation, and development, including mir-21. These results provide new insight into the molecular pathogenesis of TFI with significant implications for new strategies for treatment and prevention of chlamydial complications.

High-throughput proteomic screening identifies Chlamydia trachomatis antigens that are capable of eliciting T cell and antibody responses that provide protection against vaginal challenge

A comprehensive proteomic screening technology was previously used to characterize T cell responses to Chlamydia trachomatis infection. In this study, we demonstrated that T cells specific for protein antigens identified through this comprehensive technology home to the site of infection after mucosal challenge with C. trachomatis. In addition, T cell responses to these proteins were elicited in multiple genetic backgrounds. Two protein antigens, CT823 and CT144, were evaluated as vaccine candidates. When administered with AbISCO-100 adjuvant, these antigens stimulated potent CD8(+) T cell responses, polyfunctional T(H)1-polarized CD4(+) T cell responses, and high titer protein-specific T(H)1-skewed antibody responses. Vaccination with either antigen with AbISCO-100 provided long-lived protection against intravaginal challenge with C. trachomatis. Adoptive transfer of immune T cells also conferred protection in the challenge model whereas passive transfer of immune serum did not, indicating the critical role for T cell responses in control of this infection. The ability of these antigens to induce potent immune responses and provide long-lived protection in response to challenge provides a basis for the rational design of a C. trachomatis subunit vaccine.

CD4+ T cells are necessary and sufficient to confer protection against Chlamydia trachomatis infection in the murine upper genital tract

Chlamydia trachomatis infection is the most common bacterial sexually transmitted disease in the United States. Chlamydia infections that ascend to the upper genital tract can persist, trigger inflammation, and result in serious sequelae such as infertility. However, mouse models in which the vaginal vault is inoculated with C. trachomatis do not recapitulate the course of human disease. These intravaginal infections of the mouse do not ascend efficiently to the upper genital tract, do not cause persistent infection, do not induce significant inflammation, and do not induce significant CD4⁺ T cell infiltration. In this article, we describe a noninvasive transcervical infection model in which we bypass the cervix and directly inoculate C. trachomatis into the uterus. We show that direct C. trachomatis infection of the murine upper genital tract stimulates a robust Chlamydia-specific CD4⁺ T cell response that is both necessary and sufficient to clear infection and provide protection against reinfection.

Modulation of MICA on the surface of Chlamydia trachomatis-infected endocervical epithelial cells promotes NK cell-mediated killing

Chlamydia trachomatis serovars D-K are obligate intracellular bacteria that have tropism for the columnar epithelial cells of the genital tract. Chlamydia trachomatis infection has been reported to induce modifications in immune cell ligand expression on epithelial host cells. In this study, we used an in vitro infection model that resulted in a partial infection of C. trachomatis-exposed primary-like immortalized endocervical epithelial cells (A2EN). Using this model, we demonstrated that expression of the natural killer (NK) cell activating ligand, MHC class I-related protein A (MICA), was upregulated on C. trachomatis-infected, but not on noninfected bystander cells. MICA upregulation was concomitant with MHC class I downregulation and impacted the susceptibility of C. trachomatis-infected cells to NK cell activity. The specificity of MICA upregulation was reflected by a higher cytolytic activity of an NK cell line (NK92MI) against C. trachomatis-infected cells compared with uninfected control cells. Significantly, data also indicated that NK cells exerted a partial, but incomplete sterilizing effect on C. trachomatis as shown by the reduction in recoverable inclusion forming units (IFU) when cocultured with C. trachomatis-infected cells. Taken together, our data suggest that NK cells may play a significant role in the ability of the host to counter C. trachomatis infection.

Chlamydia trachomatis infections of the female genital tract: state of the art

Chlamydia trachomatis (CT) is the most common bacterial cause of sexually transmitted infections. CT infections are strongly associated with risk-taking behavior. Recommendations for testing have been implemented in many countries. The effectiveness of the screening programs has been questioned since chlamydia rates have increased. However, the complication rates including pelvic inflammatory disease, tubal factor infertility, and tubal pregnancy have been decreasing, which is good news. The complication rates associated with CT infection have clearly been over-estimated. Genetic predisposition and host immune response play important roles in the pathogenesis of long-term complications. CT plays a co-factor role in the development of cervical neoplasia caused by high-risk human papillomavirus (HPV) types. The evidence linking CT and other adverse pregnancy outcomes is weak. The current nucleic acid amplification tests perform well. A new genetic variant of CT was discovered in Sweden but has only rarely been detected elsewhere. Single-dose azithromycin remains effective against CT. Secondary prevention by screening is still the most important intervention to limit the adverse effects of CT on reproductive health.

Chlamydia trachomatis immune evasion via downregulation of MHC class I surface expression involves direct and indirect mechanisms

Genital C. trachomatis infections typically last for many months in women. This has been attributed to several strategies by which C. trachomatis evades immune detection, including well-described methods by which C. trachomatis decreases the cell surface expression of the antigen presenting molecules major histocompatibility complex (MHC) class I, MHC class II, and CD1d in infected genital epithelial cells. We have harnessed new methods that allow for separate evaluation of infected and uninfected cells within a mixed population of chlamydia-infected endocervical epithelial cells to demonstrate that MHC class I downregulation in the presence of C. trachomatis is mediated by direct and indirect (soluble) factors. Such indirect mechanisms may aid in priming surrounding cells for more rapid immune evasion upon pathogen entry and help promote unfettered spread of C. trachomatis genital infections.

Tumor necrosis factor alpha production from CD8+ T cells mediates oviduct pathological sequelae following primary genital Chlamydia muridarum infection

The immunopathogenesis of Chlamydia trachomatis-induced oviduct pathological sequelae is not well understood. Mice genetically deficient in perforin (perforin(-/-) mice) or tumor necrosis factor alpha (TNF-α) production (TNF-α(-/-) mice) displayed comparable vaginal chlamydial clearance rates but significantly reduced oviduct pathology (hydrosalpinx) compared to that of wild-type mice. Since both perforin and TNF-α are effector mechanisms of CD8(+) T cells, we evaluated the role of CD8(+) T cells during genital Chlamydia muridarum infection and oviduct sequelae. Following vaginal chlamydial challenge, (i) mice deficient in TAP I (and therefore the major histocompatibility complex [MHC] I pathway and CD8(+) T cells), (ii) wild-type mice depleted of CD8(+) T cells, and (iii) mice genetically deficient in CD8 (CD8(-/-) mice) all displayed similar levels of vaginal chlamydial clearance but significantly reduced hydrosalpinx, compared to those of wild-type C57BL/6 mice, suggesting a role for CD8(+) T cells in chlamydial pathogenesis. Repletion of CD8(-/-) mice with wild-type or perforin(-/-), but not TNF-α(-/-), CD8(+) T cells at the time of challenge restored hydrosalpinx to levels observed in wild-type C57BL/6 mice, suggesting that TNF-α production from CD8(+) T cells is important for pathogenesis. Additionally, repletion of TNF-α(-/-) mice with TNF-α(+/+) CD8(+) T cells significantly enhanced the incidence of hydrosalpinx and oviduct dilatation compared to those of TNF-α(-/-) mice but not to the levels found in wild-type mice, suggesting that TNF-α production from CD8(+) T cells and non-CD8(+) cells cooperates to induce optimal oviduct pathology following genital chlamydial infection. These results provide compelling new evidence supporting the contribution of CD8(+) T cells and TNF-α production to Chlamydia-induced reproductive tract sequelae.

Systemic effector and regulatory immune responses to chlamydial antigens in trachomatous trichiasis

Trachomatous trichiasis (TT) caused by repeated or chronic ocular infection with Chlamydia trachomatis is the result of a pro-fibrotic ocular immune response. At the conjunctiva, the increased expression of both inflammatory (IL1B, TNF) and regulatory cytokines (IL10) have been associated with adverse clinical outcomes. We measured in vitro immune responses of peripheral blood to a number of chlamydial antigens. Peripheral blood effector cells (CD4, CD69, IFNγ, IL-10) and regulatory cells (CD4, CD25, FOXP3, CTLA4/GITR) were readily stimulated by C. trachomatis antigens but neither the magnitude (frequency or stimulation index) or the breadth and amount of cytokines produced in vitro [IL-5, IL-10, IL-12 (p70), IL-13, IFNγ, and TNFα] were significantly different between TT cases and their non-diseased controls. Interestingly we observed that CD4+ T cells account for <50% of the IFNγ positive cells induced following stimulation. Further investigation in individuals selected from communities where exposure to ocular infection with C. trachomatis is endemic indicated that CD3-CD56+ (classical natural killer cells) were a major early source of IFNγ production in response to C. trachomatis elementary body stimulation and that the magnitude of this response increased with age. Future efforts to unravel the contribution of the adaptive immune response to conjunctival fibrosis should focus on the early events following infection and the interaction with innate immune mediated mechanisms of inflammation in the conjunctiva.

Association of tubal factor infertility with elevated antibodies to Chlamydia trachomatis caseinolytic protease P

OBJECTIVE

The objective of the study was to assess antibodies against Chlamydia trachomatis heat shock proteins (HSP) in patients with tubal factor infertility (TFI), infertility controls (IFC), and fertile controls (FC). HSPs assist organisms in surviving caustic environments such as heat.

STUDY DESIGN

Twenty-one TFI, 15 IFC, and 29 FC patients were enrolled after laparoscopic tubal assessment. The titers of antibodies against C trachomatis organisms and 14 chlamydial HSPs were compared among the 3 groups.

RESULTS

TFI patients developed significantly higher levels of antibodies against C trachomatis and specifically recognizing chlamydial HSP60 and caseinolytic protease (Clp) P, a subunit of the ATP-dependent Clp protease complex involved in the degradation of abnormal proteins.

CONCLUSION

In addition to confirming high titers of antibodies against C trachomatis organisms and HSP60 in TFI patients, we identified a novel link of TFI with anti-ClpP antibodies. These findings may provide useful information for developing a noninvasive screening test for TFI and constructing subunit anti-C trachomatis vaccines.

A new murine model for testing vaccines against genital Chlamydia trachomatis infections in males

Two groups of 50 BALB/c male mice were immunized with live Chlamydia trachomatis mouse pneumonitis (MoPn) using the intranasal (i.n.) or the meatus urethra (intraurethral: i.u.) routes. As a control group, 100 male mice were sham-immunized in parallel. Both groups of animals vaccinated with live organisms developed strong Chlamydia-specific humoral and cell mediated immune responses. Based on the IgG2a/IgG1 ratio and the levels of IFN-γ both groups mounted a Th1 immune response. At six weeks following the immunization, all mice were challenged in the meatus urethra. The urethra, urinary bladder, testes and epididymides were harvested at weekly intervals and tested for the presence of C. trachomatis. Based on the culture results from these four organs both groups of Chlamydia-immunized mice showed significant protection. In the group immunized i.u., 10% (5/50) had positive cultures, while in the group immunized i.n. 28% (14/50) had positive cultures during the 5 weeks of observation. In contrast, in the sham-immunized animals 47% (47/100) had positive cultures (P<0.005) during the study period. In addition, the number of positive organs, the length of time that the animal had positive cultures, and the total number of inclusion forming units (IFU) recovered were overall significantly lower in the i.u. or i.n. groups in comparison with the sham-immunized animals. However, in relation to the i.u. immunized group, the protection elicited in the i.n. group was delayed and not as robust. In conclusion, immunization of mice in the meatus urethra may provide the gold standard for testing Chlamydia vaccines in a male model.