The recall response induced by genital challenge with Chlamydia muridarum protects the oviduct from pathology but not from reinfection

Immunity to Sexually Transmitted Bacterial Infections of the Female Genital Tract: Toward Effective Vaccines

Sexually transmitted infections (STIs) caused by bacterial pathogens Chlamydia trachomatis, Neisseria gonorrhoeae, and Treponema pallidum present significant public health challenges. These infections profoundly impact reproductive health, leading to pelvic inflammatory disease, infertility, and increased susceptibility to other infections. Prevention measures, including antibiotic treatments, are limited by the often-asymptomatic nature of these infections, the need for repetitive and continual screening of sexually active persons, antibiotic resistance for gonorrhea, and shortages of penicillin for syphilis. While vaccines exist for viral STIs like human papillomavirus (HPV) and hepatitis B virus (HBV), there are no vaccines available for bacterial STIs. This review examines the immune responses in the female genital tract to these bacterial pathogens and the implications for developing effective vaccines against bacterial STIs.

Viral-vectored boosting of OmcB- or CPAF-specific T-cell responses fail to enhance protection from Chlamydia muridarum in infection-immune mice and elicits a non-protective CD8-dominant response in naïve mice

A vaccine is needed to combat the Chlamydia epidemic. Replication-deficient viral vectors are safe and induce antigen-specific T-cell memory. We tested the ability of intramuscular immunization with modified vaccinia Ankara (MVA) virus or chimpanzee adenovirus (ChAd) expressing chlamydial outer membrane protein (OmcB) or the secreted protein, chlamydial protease-like activating factor (CPAF), to enhance T-cell immunity and protection in mice previously infected with plasmid-deficient Chlamydia muridarum CM972 and elicit protection in naïve mice. MVA.OmcB or MVA.CPAF increased antigen-specific T cells in CM972-immune mice ∼150 and 50-fold, respectively, but failed to improve bacterial clearance. ChAd.OmcB/MVA.OmcB prime-boost immunization of naïve mice elicited a cluster of differentiation (CD) 8-dominant T-cell response dominated by cluster of differentiation (CD)8 T cells that failed to protect. ChAd.CPAF/ChAd.CPAF prime-boost also induced a CD8-dominant response with a marginal reduction in burden. Challenge of ChAd.CPAF-immunized mice genetically deficient in CD4 or CD8 T cells showed that protection was entirely CD4-dependent. CD4-deficient mice had prolonged infection, whereas CD8-deficient mice had higher frequencies of CPAF-specific CD4 T cells, earlier clearance, and reduced burden than wild-type controls. These data reinforce the essential nature of the CD4 T-cell response in protection from chlamydial genital infection in mice and the need for vaccine platforms that drive CD4-dominant responses.

Analysis of immune response induction mechanisms implicating the dose-sparing effect of transcutaneous immunization using a self-dissolving microneedle patch

Transcutaneous immunization (TCI) is an effective vaccination method that is easier and less painful than the conventional injectable vaccination method. We previously developed self-dissolving microneedle patches (sdMN) and demonstrated that this TCI method has a high vaccination efficacy in mice and humans. To elucidate the mechanism of immune response induction, which is the basis for the efficacy and safety of TCI with sdMN, we examined the local reaction of the skin where sdMN was applied and the kinetics and differentiation status of immune cells in the draining lymph nodes (DLNs). We found that gene expression of the proinflammatory cytokine Il1b and the downstream transcription factor Irf7 was markedly upregulated in skin tissues after sdMN application. Moreover, activation of Langerhans cells and CD207^- dermal dendritic cells, which are subsets of antigen-presenting cells (APCs) in the skin, and their migration to the DLNs were promoted. Furthermore, the activated APC subsets promoted CD4⁺ T cell and B cell differentiation and the formation of germinal centers, which are the sites of high-affinity antibody production. These phenomena associated with sdMN application may contribute to the efficient production of antigen-specific antibodies after TCI using sdMN. These findings provide essential information regarding immune response induction mechanisms for the development and improvement of TCI preparations.

Pelvic Inflammatory Disease Due to Neisseria gonorrhoeae and Chlamydia trachomatis: Immune Evasion Mechanisms and Pathogenic Disease Pathways

Pelvic inflammatory disease (PID) results from ascension of sexually transmitted pathogens from the lower genital tract to the uterus and/or fallopian tubes in women, with potential spread to neighboring pelvic organs. Patients may present acutely with lower abdominal or pelvic pain and pelvic organ tenderness. Many have subtle symptoms or are asymptomatic and present later with tubal factor infertility, ectopic pregnancy, or chronic pelvic pain. Neisseria gonorrhoeae and Chlamydia trachomatis are the 2 most commonly recognized PID pathogens. Their ability to survive within host epithelial cells and neutrophils highlights a need for T-cell-mediated production of interferon γ in protection. Data indicate that for both pathogens, antibody can accelerate clearance by enhancing opsonophagocytosis and bacterial killing when interferon γ is present. A study of women with N. gonorrhoeae- and/or C. trachomatis-induced PID with histologic endometritis revealed activation of myeloid cell, cell death, and innate inflammatory pathways in conjunction with dampening of T-cell activation pathways. These findings are supported by multiple studies in mouse models of monoinfection with N. gonorrhoeae or Chlamydia spp. Both pathogens exert multiple mechanisms of immune evasion that benefit themselves and each other at the expense of the host. However, similarities in host immune mechanisms that defend against these 2 bacterial pathogens instill optimism for the prospects of a combined vaccine for prevention of PID and infections in both women and men.

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.

IL-1α Is Essential for Oviduct Pathology during Genital Chlamydial Infection in Mice

Chlamydia trachomatis infection of the female genital tract can lead to irreversible fallopian tube scarring. In the mouse model of genital infection using Chlamydia muridarum, IL-1R signaling plays a critical role in oviduct tissue damage. In this study, we investigated the pathologic role of IL-1α, one of the two proinflammatory cytokines that bind to IL-1R. Il1a^-/- mice infected with C. muridarum cleared infection at their cervix at the same rate as wild-type (WT) mice, but were significantly protected from end point oviduct damage and fibrosis. The contribution of IL-1α to oviduct pathology was more dramatic than observed in mice deficient for IL-1β. Although chlamydial burden was similar in WT and Il1a^-/- oviduct during peak days of infection, levels of IL-1β, IL-6, CSF3, and CXCL2 were reduced in Il1a^-/- oviduct lysates. During infection, Il1a^-/- oviducts and uterine horns exhibited reduced neutrophil infiltration, and this reduction persisted after the infection resolved. The absence of IL-1α did not compromise CD4 T cell recruitment or function during primary or secondary chlamydial infection. IL-1α is expressed predominantly by luminal cells of the genital tract in response to infection, and low levels of expression persisted after the infection cleared. Ab-mediated depletion of IL-1α in WT mice prevented infection-induced oviduct damage, further supporting a key role for IL-1α in oviduct pathology.

Chlamydia-infected macrophages are resistant to azithromycin treatment and are associated with chronic oviduct inflammation and hydrosalpinx development

Chlamydia infection remains the leading sexually-transmitted bacterial infection worldwide, causing damaging sequelae such as tubal scarring, infertility and ectopic pregnancy. As infection is often asymptomatic, prevention via vaccination is the optimal strategy for disease control. Vaccination strategies aimed at preventing bacterial infection have shown some promise, although these strategies often fail to prevent damaging inflammatory pathology when Chlamydia is encountered. Using a murine model of Chlamydia muridarum genital infection, we employed two established independent models to compare immune responses underpinning pathologic development of genital Chlamydia infection. Model one uses antibiotic treatment during infection, with only early treatment preventing pathology. Model two uses a plasmid-cured variant strain of C. muridarum that does not cause pathologic outcomes like the plasmid-containing wild-type counterpart. Using these infection models, contrasted by the development of pathology, we identified an unexpected role for macrophages. We observed that mice showing signs of pathology had greater numbers of activated macrophages present in the oviducts. This may have been due to early differences in macrophage activation and proinflammatory signaling leading to persistent or enhanced infection. These results provide valuable insight into the cellular mechanisms driving pathology in Chlamydia infection and contribute to the design and development of more effective vaccine strategies for protection against the deleterious sequelae of Chlamydia infection of the female reproductive tract.

Discovery of Blood Transcriptional Endotypes in Women with Pelvic Inflammatory Disease

Sexually transmitted infections with Chlamydia trachomatis and/or Neisseria gonorrhoeae and rates of pelvic inflammatory disease (PID) in women continue to rise, with reinfection being common because of poor adaptive immunity. Diagnosis remains imprecise, and pathogenesis data are derived primarily from monoinfection of mice with C. trachomatis or N. gonorrhoeae By comparing blood mRNA responses of women with C. trachomatis- and/or N. gonorrhoeae-induced PID and histologic endometritis with those from women with C. trachomatis and/or N. gonorrhoeae infection limited to their cervix and asymptomatic uninfected women determined via microarray, we discovered important pathogenic mechanisms in PID and response differences that provide a pathway to biomarker discovery. Women with N. gonorrhoeae- and/or C. trachomatis-induced PID exhibit overexpression of myeloid cell genes and suppression of protein synthesis, mitochondrial oxidative phosphorylation, and T cell-specific genes. Coinfected women exhibited the greatest activation of cell death pathways and suppression of responses essential for adaptive immunity. Women solely infected with C. trachomatis expressed elevated levels of type I and type II IFN genes, and enhanced type I IFN-induced chemokines in cervical secretions were associated with ascension of C. trachomatis to the endometrium. Blood microarrays reveal discrete pathobiological endotypes in women with PID that are driven by pathogen invasion of the upper genital tract.

Development of a Chlamydia trachomatis vaccine for urogenital infections: novel tools and new strategies point to bright future prospects

INTRODUCTION

The "cloaked" bacterial pathogen that is Chlamydia trachomatis continues to cause sexually transmitted infections (STIs) that adversely affect the health and well-being of children, adolescents and adults globally. The reproductive disease sequelae follow unresolved or untreated chronic or recurrent asymptomatic C.trachomatis infections of the lower female genital tract (FGT) and can include pelvic pain, pelvic inflammatory disease (PID) and ectopic pregnancy. Tubal Factor Infertility (TFI) can also occur since protective and long-term natural immunity to chlamydial infection is incomplete, allowing for ascension of the organism to the upper FGT. Developing countries including the WHO African (8.3 million cases) and South-East Asian regions (7.2 million cases) bear the highest burden of chlamydial STIs.

AREAS COVERED

Genetic advances for Chlamydia have provided tools for transformation (including dendrimer-enabled transformation), lateral gene transfer and chemical mutagenesis. Recent progress in these areas is reviewed with a focus on vaccine development for Chlamydia infections of the female genital tract.

EXPERT COMMENTARY

A vaccine that can elicit immuno-protective responses whilst avoiding adverse immuno-pathologic host responses is required. The current technological advances in chlamydial genetics and proteomics, as well as novel and improved adjuvants and delivery systems, provide new hope that the elusive chlamydial vaccine is an imminent and realistic goal.

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.

Vaccination with the polymorphic membrane protein A reduces Chlamydia muridarum induced genital tract pathology

Chlamydia trachomatis serovars D-K are one of the most frequent causes of sexually transmitted infections of the female genital tract, with possible complications such as hydrosalpinx, pelvic inflammatory disease, extra-uterine gravidity or infertility. We used the murine genital tract infection model with C. muridarum for vaccination studies and found that more than 70% of the infected mice suffered from uterus dilatations and/or hydrosalpinx. Systemic consequences of the vaginal infection were apparent by splenomegaly ten to fifteen days post infection. While cultivable microorganisms were detectable for the first 23days post infection, the first lesions of the genital tract developed at day 15, however, many lesions occurred later in the absence of cultivable bacteria. Lesions were not accompanied by pro-inflammatory cytokines such as IFNɣ, TNF and IL-6, since these cytokines were almost undetectable in the genital tract 43days post infection. To prevent genital tract lesions, we vaccinated mice with the polymorphic membrane protein (Pmp) A in combination with CpG-ODN 1826 as adjuvant. The vaccine lowered the chlamydial burden and the differences were significant at day 10 post infection but not later. More importantly the vaccine decreased the rate and severity of genital tract lesions. Interestingly, control vaccination with the protein ovalbumin plus CpG-ODN 1826 enhanced significantly the severity but not the rate of pathologic lesions, which was presumably caused by the activation of innate immune responses by the adjuvant in the absence of a C. muridarum-specific adaptive immune response. In summary, vaccination with recombinant PmpA plus CpG-ODN 1826 significantly reduced C. muridarum-induced tissue damage, however, CpG-ODN 1826 may aggravate C. muridarum-induced tissue injuries in the absence of a protective antigen.

Collateral Damage: Detrimental Effect of Antibiotics on the Development of Protective Immune Memory

Antibiotic intervention is an effective treatment strategy for many bacterial infections and liberates bacterial antigens and stimulatory products that can induce an inflammatory response. Despite the opportunity for bacterial killing to enhance the development of adaptive immunity, patients treated successfully with antibiotics can suffer from reinfection. Studies in mouse models of Salmonella and Chlamydia infection also demonstrate that early antibiotic intervention reduces host protective immunity to subsequent infection. This heightened susceptibility to reinfection correlates with poor development of Th1 and antibody responses in antibiotic-treated mice but can be overcome by delayed antibiotic intervention, thus suggesting a requirement for sustained T cell stimulation for protection. Although the contribution of memory T cell subsets is imperfectly understood in both of these infection models, a protective role for noncirculating memory cells is suggested by recent studies. Together, these data propose a model where antibiotic treatment specifically interrupts tissue-resident memory T cell formation. Greater understanding of the mechanistic basis of this phenomenon might suggest therapeutic interventions to restore a protective memory response in antibiotic-treated patients, thus reducing the incidence of reinfection.

Chlamydia trachomatis Genital Infections

Etiology, transmission and protection: Chlamydia trachomatis is the leading cause of bacterial sexually transmitted infection (STI) globally. However, C. trachomatis also causes trachoma in endemic areas, mostly Africa and the Middle East, and is a leading cause of preventable blindness worldwide. Epidemiology, incidence and prevalence: The World Health Organization estimates 131 million new cases of C. trachomatis genital infection occur annually. Globally, infection is most prevalent in young women and men (14-25 years), likely driven by asymptomatic infection, inadequate partner treatment and delayed development of protective immunity. Pathology/Symptomatology: C. trachomatis infects susceptible squamocolumnar or transitional epithelial cells, leading to cervicitis in women and urethritis in men. Symptoms are often mild or absent but ascending infection in some women may lead to Pelvic Inflammatory Disease (PID), resulting in reproductive sequelae such as ectopic pregnancy, infertility and chronic pelvic pain. Complications of infection in men include epididymitis and reactive arthritis. Molecular mechanisms of infection: Chlamydiae manipulate an array of host processes to support their obligate intracellular developmental cycle. This leads to activation of signaling pathways resulting in disproportionate influx of innate cells and the release of tissue damaging proteins and pro-inflammatory cytokines. Treatment and curability: Uncomplicated urogenital infection is treated with azithromycin (1 g, single dose) or doxycycline (100 mg twice daily x 7 days). However, antimicrobial treatment does not ameliorate established disease. Drug resistance is rare but treatment failures have been described. Development of an effective vaccine that protects against upper tract disease or that limits transmission remains an important goal.

Genital Chlamydia trachomatis: understanding the roles of innate and adaptive immunity in vaccine research

Chlamydia trachomatis is the leading cause of bacterial sexually transmitted disease worldwide, and despite significant advances in chlamydial research, a prophylactic vaccine has yet to be developed. This Gram-negative obligate intracellular bacterium, which often causes asymptomatic infection, may cause pelvic inflammatory disease (PID), ectopic pregnancies, scarring of the fallopian tubes, miscarriage, and infertility when left untreated. In the genital tract, Chlamydia trachomatis infects primarily epithelial cells and requires Th1 immunity for optimal clearance. This review first focuses on the immune cells important in a chlamydial infection. Second, we summarize the research and challenges associated with developing a chlamydial vaccine that elicits a protective Th1-mediated immune response without inducing adverse immunopathologies.

Chlamydia trachomatis: Protective Adaptive Responses and Prospects for a Vaccine

Chlamydia trachomatis is the most common cause of sexually transmitted bacterial infection globally. These infections translate to a significant public health burden, particularly women's healthcare costs due to serious disease sequelae such as pelvic inflammatory disease (PID), tubal factor infertility, chronic pelvic pain, and ectopic pregnancy. There is no evidence that natural immunity can provide complete, long-term protection necessary to prevent chronic pathology, making human vaccine development critical. Vaccine design will require careful consideration of protective versus pathological host-response mechanisms in concert with elucidation of optimal antigens and adjuvants. Evidence suggests that a Th1 response, facilitated by IFN-γ-producing CD4 T cells, will be instrumental in generating long-term, sterilizing immunity. Although the role of antibodies is not completely understood, they have exhibited a protective effect by enhancing chlamydial clearance. Future work will require investigation of broadly neutralizing antibodies and antibody-augmented cellular immunity to successfully design a vaccine that potently elicits both arms of the immune response. Sterilizing immunity is the ultimate goal. However, vaccine-induced partial immunity that prevents upper genital tract infection and inflammation would be cost-effective compared to current screening and treatment strategies. In this chapter, we examine evidence from animal and human studies demonstrating protective adaptive immune responses to Chlamydia and discuss future challenges and prospects for vaccine development.

The p47phox deficiency significantly attenuates the pathogenicity of Chlamydia muridarum in the mouse oviduct but not uterine tissues

The Chlamydia muridarum induction of the upper genital tract pathology in mice has been used to investigate the mechanisms of chlamydial pathogenesis. We report that the NCF1 (neutrophil cytosolic factor1)-encoded p47phox (phagocyte oxidase), an essential subunit of nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase, contributes significantly to C. muridarum induction of hydrosalpinx. Mice lacking p47phox (p47phox-deficient) were no longer able to develop significant hydrosalpinx following an intravaginal infection with C. muridarum. However, there was no significant difference in uterine horn dilation (as a result of the endometrial glandular duct dilation) between the p47phox-deficient and -sufficient mice. Thus, the role of NADPH oxidase in chlamydial pathogenesis is restricted to the oviduct tissue rather than the entire upper genital tract. Interestingly, both the p47phox-deficient and -sufficient mice displayed similar levels of chlamydial live organism shedding from the lower genital tract, suggesting that the NADPH oxidase is not required for the mouse control of chlamydial infection in the lower genital tract. Furthermore, the p47phox deficiency did not affect the infectious organism burden in the upper genital tract tissues, indicating that the NADPH-oxidase activity is not necessary for the mouse prevention of chlamydial ascension from the lower to upper genital tracts. However, the p47phox-defieicnt mice displayed a significantly reduced chronic inflammatory infiltration in the oviduct but not uterine tissues, supporting the finding that the NADPH oxidase activity is required for chlamydial induction of dilation in the oviduct but not the endometrial glandular duct. Thus, we have demonstrated a significant role of the host NADPH oxidase in promoting chronic inflammatory pathology in the oviduct following chlamydial infection.

Quantitative In Vivo Detection of Chlamydia muridarum Associated Inflammation in a Mouse Model Using Optical Imaging

Chlamydia trachomatis is a bacterial sexually transmitted disease with over 1.3 million cases reported to the CDC in 2010. While Chlamydia infection is easily treated with antibiotics, up to 70% of infections are asymptomatic and go untreated. The current mouse model relies on invasive upper genital tract gross pathology readouts at ~60-80 days postinfection. High throughput optical imaging through the use of biomarkers has been successfully used to quickly evaluate several disease processes. Here we evaluate Neutrophil Elastase 680 (Elastase680) for its ability to measure Chlamydia muridarum associated inflammation in live mice using fluorescence molecular tomography (FMT) and In Vivo Imaging System (IVIS). Optical imaging was able to distinguish with statistical significance between vaccinated and nonvaccinated mice as well as mock-challenged and challenged mice 2 weeks after challenge which was 9 weeks sooner than typical gross pathological assessment. Immunohistochemistry confirmed the presence of neutrophils and correlated well with both in vivo and ex vivo imaging. In this report we demonstrate that Elastase680 can be used as a molecular imaging biomarker for inflammation associated with chlamydial infection in a mouse model and that these biomarkers can significantly decrease the time for pathology evaluation and thus increase the rate of therapeutics discovery.

Comparable Genital Tract Infection, Pathology, and Immunity in Rhesus Macaques Inoculated with Wild-Type or Plasmid-Deficient Chlamydia trachomatis Serovar D

Rhesus macaques were studied to directly address the potential for plasmid-deficient Chlamydia trachomatis to serve as a live attenuated vaccine in the genital tract. Five repeated cervical inoculations of rhesus macaques with wild-type serovar D strain D/UW-3/Cx or a plasmid-deficient derivative of this strain, CTD153, resulted in infections with similar kinetics and induced comparable levels of protective immunity. After all animals received five challenges with D/UW-3/Cx, levels of inflammation observed grossly and histologically were similar between the groups. Animals in both groups developed evidence of oviduct dilatation; however, reduced oviduct dilatation was observed for "controllers," i.e., animals without detectable chlamydial DNA in the fimbriae at weeks 5 and 12. Grouping animals into "ascenders" and "controllers" revealed that elevated early T cell responses were associated with protection, whereas higher antibody responses were associated with ascension. Protected animals shared common major histocompatibility complex (MHC) alleles. Overall, genetic differences of individual animals, rather than the presence or absence of the chlamydial plasmid in the primary infecting strain, appeared to play a role in determining the outcome of infection.

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

PURPOSE

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

PROCEDURES

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

RESULTS

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

CONCLUSION

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

Frequency of Chlamydia trachomatis-specific T cell interferon-γ and interleukin-17 responses in CD4-enriched peripheral blood mononuclear cells of sexually active adolescent females

An evaluation of CD4 T cell responses to candidate Chlamydia trachomatis vaccine antigens was conducted in an adolescent female cohort exposed through natural infection to explore antigen immunogenicity and correlation with protection from reinfection. The frequency of peripheral blood CD4 T cell IFN-γ and IL-17 responses to three candidate vaccine antigens, polymorphic membrane protein G (PmpG), F (PmpF), and major outer membrane protein (MOMP), were determined by ELISPOT; responses to chlamydial heat shock protein 60 (HSP60) and to elementary bodies (EB) were included for comparison. Responses of Infected (n=8), Seropositive/Uninfected (n=13), and Seronegative/Uninfected (n=18) participants were compared. The median CD4 IFN-γ response to EB was significantly increased in Infected (P=0.003) and Seropositive/Uninfected (P=0.002) versus Seronegative/Uninfected female subjects. Higher rates of positive IFN-γ responders to EB, PmpF, and MOMP were detected in Seropositive/Uninfected versus Seronegative/Uninfected participants (P=0.021). IL-17 responses were generally low. A positive IFN-γ response to any of the antigens tested was associated with a trend toward a reduced risk of reinfection, although not statistically significant. Among this adolescent cohort, chlamydial-specific CD4 IFN-γ but not IL-17 responses were detected in acutely and previously infected participants and a positive CD4 IFN-γ response was associated with a non-significant reduced risk of reinfection.

Steroids alone or as adjunctive therapy with doxycycline fail to improve oviduct damage in mice infected with Chlamydia muridarum

In women, Chlamydia trachomatis can ascend from the cervix to the fallopian tubes, where an overly aggressive host inflammatory response can cause scarring that leads to chronic pelvic pain, infertility, or ectopic pregnancy. Although screening and treatment programs for women have resulted in decreased rates of sequelae, morbidities associated with oviduct scarring continue to occur. Since corticosteroids have anti-inflammatory and antifibrotic effects, we tested the ability of dexamethasone to inhibit inflammation and prevent oviduct scarring in mice genitally infected with Chlamydia muridarum. The administration of 1 or 2.5 mg/kg of body weight of dexamethasone on days 7 to 21 of infection resulted in reduced accumulation of inflammatory cells in the oviducts compared to that in controls. However, a concomitant increase in bacterial burden was observed, and chronic oviduct disease was not reduced. Adjunctive administration of a prolonged (21-day) or short (3-day) course of dexamethasone in combination with the antibiotic doxycycline also failed to reduce chronic oviduct pathology compared to antibiotic treatment alone. Steroids administered alone or adjunctively with antibiotics failed to prevent oviduct damage in this murine model of C. trachomatis infection.

IL-23 induces IL-22 and IL-17 production in response to Chlamydia muridarum genital tract infection, but the absence of these cytokines does not influence disease pathogenesis

OBJECTIVE

Chlamydia trachomatis infections are a significant cause of reproductive tract pathology. Protective and pathological immune mediators must be differentiated to design a safe and effective vaccine.

METHODS

Wild-type mice and mice deficient in IL-22 and IL-23 were infected intravaginally with Chlamydia muridarum, and their course of infection and oviduct pathology were compared. Local genital tract and draining lymph node immune responses were also examined in IL-23-deficient mice.

RESULTS

IL-22- and IL-23-deficient mice exhibited normal susceptibility to infection and oviduct pathology. IL-23 was required for the development of a Chlamydia-specific Th17 response in the lymph nodes and for production of IL-22 and IL-17 in the genital tract. However, influx of Th1 and innate immune cells was not compromised in the absence of IL-23.

CONCLUSION

IL-22 and IL-23 play either redundant or minimal roles in the pathogenesis of Chlamydia infection in the mouse model. Induction of Th17-associated cytokines by a Chlamydia vaccine should be avoided as these responses are not central to resolution of infection and have pathologic potential.

CD4+ T cell expression of MyD88 is essential for normal resolution of Chlamydia muridarum genital tract infection

Resolution of Chlamydia genital tract infection is delayed in the absence of MyD88. In these studies, we first used bone marrow chimeras to demonstrate a requirement for MyD88 expression by hematopoietic cells in the presence of a wild-type epithelium. Using mixed bone marrow chimeras we then determined that MyD88 expression was specifically required in the adaptive immune compartment. Furthermore, adoptive transfer experiments revealed that CD4(+) T cell expression of MyD88 was necessary for normal resolution of genital tract infection. This requirement was associated with a reduced ability of MyD88(-/-)CD4(+) T cells to accumulate in the draining lymph nodes and genital tract when exposed to the same inflammatory milieu as wild-type CD4(+) T cells. We also demonstrated that the impaired infection control we observed in the absence of MyD88 could not be recapitulated by deficiencies in TLR or IL-1R signaling. In vitro, we detected an increased frequency of apoptotic MyD88(-/-)CD4(+) T cells upon activation in the absence of exogenous ligands for receptors upstream of MyD88. These data reveal an intrinsic requirement for MyD88 in CD4(+) T cells during Chlamydia infection and indicate that the importance of MyD88 extends beyond innate immune responses by directly influencing adaptive immunity.

From mice to women and back again: causalities and clues for Chlamydia-induced tubal ectopic pregnancy

OBJECTIVE

To provide an overview of knockout mouse models that have pathological tubal phenotypes after Chlamydia muridarum infection, discuss factors and pathological processes that contribute to inflammation, summarize data on tubal transport and progression of tubal implantation from studies in humans and animal models, and highlight research questions in the field.

DESIGN

A search of the relevant literature using PubMed and other online tools.

SETTING

University-based preclinical and clinical research laboratories.

PATIENT(S)

Women with tubal ectopic pregnancy after Chlamydia trachomatis infection.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Critical review of the literature.

RESULT(S)

Chlamydia trachomatis infection poses a major threat to human reproduction. Biological and epidemiological evidence suggests that progression of Chlamydia infection causes intense and persistent inflammation, injury, and scarring in the fallopian tube, leading to a substantially increased risk of ectopic pregnancy and infertility. The main targets of Chlamydia infection are epithelial cells lining the mucosal surface, which play a central role in host immune responses and pathophysiology. Tubal phenotypes at the cellular level in mutant mice appear to reflect alterations in the balance between inflammatory mediator and factor deficiency. While studies in mice infected with Chlamydia muridarum have provided insight into potential inflammatory mediators linked to fallopian tube pathology, it is unclear how inflammation induced by Chlamydia infection prevents or retards normal tubal transport and causes embryo implantation in the fallopian tube.

CONCLUSION(S)

Given the similarities in the tubal physiology of humans and rodents, knockout mouse models can be used to study certain aspects of tubal functions, such as gamete transport and early embryo implantation. Elucidation of the exact molecular mechanisms of immune and inflammatory responses caused by Chlamydia infection in human fallopian tubal cells in vitro and understanding how Chlamydia infection affects tubal transport and implantation in animal studies in vivo may explain how Chlamydia trachomatis infection drives inflammation and develops the tubal pathology in women with tubal ectopic pregnancy.