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

Influence of cervicovaginal microbiota on Chlamydia trachomatis infection dynamics

The cervicovaginal microbiome (CVM) is increasingly being considered as an important aspect of women's health, particularly in relation to the risk and progression of sexually transmitted infections (STIs). CVM composition varies significantly between individuals and is shaped by factors including diet, age, environmental exposures, and lifestyle. Understanding these influences may shed light on how microbial imbalances contribute to infection susceptibility and the development of reproductive health disorders. Five distinct community state types (CSTs) classify common CVM compositions. Most CSTs (I, II, III, V) are characterized by a dominant Lactobacillus species and are associated with better or neutral reproductive health, including reduced coincident detection of STIs such as Chlamydia trachomatis. In contrast, CST IV is composed of diverse, predominantly anaerobic, microbial species and is associated with CVM dysbiosis, bacterial vaginosis, and a heightened risk of STI acquisition. This review examines the complex interplay between the CVM, C. trachomatis infection, and host immune responses, highlighting the role of metabolites such as short-chain and long-chain fatty acids, indole, and iron in modulating pathogen survival and host defenses. Additionally, the impacts of CVM composition on C. trachomatis persistence, ascension, and clearance are discussed, alongside co-infection dynamics with pathogens like Neisseria gonorrhoeae and Mycoplasma genitalium.

Study Models for Chlamydia trachomatis Infection of the Female Reproductive Tract

Chlamydia trachomatis (Ct) is a leading cause of sexually transmitted infections globally, often resulting in inflammatory disorders, ectopic pregnancies, and infertility. Studying Ct's pathogenesis remains challenging due to its unique life cycle and host-specific interactions, which require diverse experimental models. Animal studies using mouse, guinea pig, pig, and non-human primate models provide valuable insights into immune responses, hormonal influences, and disease progression. However, they face limitations in terms of translational relevance due to physiological differences, as well as ethical concerns. Complementing these, in vitro systems, ranging from simple monolayer to advanced three-dimensional models, exhibit improved physiological relevance by replicating the human tissue architecture. This includes the detailed investigation of epithelial barrier disruptions, epithelium-stroma interactions, and immune responses at a cellular level. Nonetheless, in vitro models fall short in mimicking the intricate tissue structures found in vivo and, therefore, cannot faithfully replicate the host-pathogen interactions or infection dynamics observed in living organisms. This review presents a comprehensive overview of the in vivo and in vitro models employed over the past few decades to investigate Ct and its pathogenesis, addressing their strengths and limitations. Furthermore, we explore emerging technologies, including organ-on-chip and in silico models, as promising tools to overcome the existing challenges and refine our understanding of Ct infections.

Chlamydia trachomatis: From Urogenital Infections to the Pathway of Infertility

Chlamydia trachomatis (CT) is a major cause of sexually transmitted infections (STIs) worldwide, with significant implications for reproductive health. The bacterium's genome contains highly polymorphic regions, influencing both the type and severity of infections. These genetic variations, particularly those occurring in the major outer membrane protein (MOMP) gene, are critical for classifying the bacterium into distinct serovars and enable CT to adapt to diverse host environments, contributing to its immune evasion, persistence, and pathogenicity. Persistent or untreated urogenital infections can lead to chronic inflammation, tissue damage, and pelvic inflammatory disease, ultimately increasing the risk of ectopic pregnancy, spontaneous abortion, and infertility. This review consolidates current knowledge on the genetic diversity of CT, its potential role in modulating infection outcomes, and its immune evasion mechanisms. By integrating scientific evidence linking chlamydial infections to infertility, we underscore the urgent need for targeted research to address this critical public health challenge.

A VCG-Based Multiepitope Chlamydia Vaccine Incorporating the Cholera Toxin A1 Subunit (MECA) Confers Protective Immunity Against Transcervical Challenge

Background/Objectives: We generated a novel recombinant Vibrio cholerae ghost (rVCG)-based subunit vaccine incorporating the A1 subunit of cholera toxin (CTA1) and a multiepitope Chlamydia trachomatis (CT) antigen (MECA) derived from five chlamydial outer membrane proteins (rVCG-MECA). The ability of this vaccine to protect against a CT transcervical challenge was evaluated. Methods: Female C57BL/6J mice were immunized thrice at two-week intervals with rVCG-MECA or rVCG-gD2 (antigen control) via the intramuscular (IM) or intranasal (IN) route. PBS-immunized mice or mice immunized with live CT served as negative and positive controls, respectively. Results: Vaccine delivery stimulated robust humoral and cell-mediated immune effectors, characterized by local mucosal and systemic CT-specific IgG, IgG2c, and IgA antibody and IFN-γ (Th1 cytokine) responses. The elicited mucosal and systemic IgG2c and IgA antibody responses persisted for 16 weeks post-immunization. Immunization with rVCG-MECA afforded protection comparable to that provided by IN immunization with live CT EBs without any side effects, irrespective of route of vaccine delivery. Conclusions: The results underline the potential of a multiepitope vaccine as a promising resource for protecting against CT genital infection and the potential of CTA1 on the VCG platform as a mucosal and systemic adjuvant for developing CT vaccines.

Pathogenic and Protective Roles of Neutrophils in Chlamydia trachomatis Infection

Chlamydia trachomatis (Ct) is an obligate intracellular pathogen that causes the most commonly diagnosed bacterial sexually transmitted infection (STI) and is a leading cause of preventable blindness globally. Ct infections can generate a strong pro-inflammatory immune response, leading to immune-mediated pathology in infected tissues. Neutrophils play an important role in mediating both pathology and protection during infection. Excessive neutrophil activation, migration, and survival are associated with host tissue damage during Chlamydia infections. In contrast, neutrophils also perform phagocytic killing of Chlamydia in the presence of IFN-γ and anti-Chlamydia antibodies. Neutrophil extracellular traps (NETs) and many neutrophil degranulation products have also demonstrated strong anti-Chlamydia functions. To counteract this neutrophil-mediated protection, Chlamydia has developed several evasion strategies. Various Chlamydia proteins can limit potentially protective neutrophil responses by directly targeting receptors present on the surface of neutrophils or neutrophil degranulation products. In this review, we provide a survey of current knowledge regarding the role of neutrophils in pathogenesis and protection, including the ways that Chlamydia circumvents neutrophil functions, and we propose critical areas for future research.

Irradiated whole cell Chlamydia vaccine confers significant protection in a murine genital tract challenge model

Chlamydia trachomatis infections are the most common bacterial STIs globally and can lead to serious morbidity if untreated. Development of a killed, whole-cell vaccine has been stymied by coincident epitope destruction during inactivation. Here, we present a prototype Chlamydia vaccine composed of elementary bodies (EBs) from the related mouse pathogen, Chlamydia muridarum (Cm). EBs inactivated by gamma rays (Ir-Cm) in the presence of the antioxidant Mn2+-Decapeptide (DEHGTAVMLK) Phosphate (MDP) are protected from epitope damage but not DNA damage. Cm EBs gamma-inactivated with MDP retain their structure and provide significant protection in a murine genital tract infection model. Mice vaccinated with Ir-Cm (+MDP) exhibited elevated levels of Cm-specific IgG and IgA antibodies, reduced bacterial burdens, accelerated clearance, and distinctive cytokine responses compared to unvaccinated controls and animals vaccinated with EBs irradiated without MDP. Preserving EB epitopes with MDP during gamma inactivation offers the potential for a polyvalent, whole-cell vaccine against C. trachomatis.

Association of Chlamydia trachomatis Infection With Breast Cancer Risk and the Modification Effect of IL-12

BACKGROUND

Chlamydia trachomatis (C. trachomatis) infection has been implicated in various cancers, yet its association with breast cancer remains unexplored. This infection triggers a cascade of immune responses primarily regulated by Interleukins-12 (IL-12). Thus, the objective of this case-control study was to investigate the link between C. trachomatis infection and breast cancer risk, as well as the modification effect of IL-12.

METHODS

We assessed IgG levels against C. trachomatis in serum of 1,121 women with breast cancer (861 with estrogen receptor-positive (ER+) and 260 with estrogen receptor-negative (ER-) tumors) and 400 controls in Guangzhou, China. Logistic regression models were applied to estimate the odds ratios (ORs) and 95% confidence intervals (95% CIs) for breast cancer risk in association with C. trachomatis infection. The interaction between C. trachomatis infection and IL-12 on breast cancer risk was estimated by the product terms in the logistic regression models.

RESULTS

Seropositivity of C. trachomatis IgG showed a slight association with an increased risk of breast cancer (OR = 1.20; 95% CI: 0.86∼1.78). This association was more pronounced among women with a higher (OR = 5.82; 95% CI: 1.31∼25.94) than a lower (OR = 0.73; 95% CI: 0.41∼1.30) level of IL-12, with a statistically significant interaction observed (Pinteraction = 0.013). In addition, C. trachomatis IgG seropositivity was related to an increased risk of breast cancer among PR+ patients (OR = 1.53; 95% CI: 1.04∼2.23).

CONCLUSIONS

C. trachomatis infection may contribute to the development of hormone-responsive breast cancer in women with high levels of IL-12. Further studies are needed to uncover the underlying mechanisms.

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

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

Chlamydia trachomatis and Neisseria gonorrhoeae rectal infections: Interplay between rectal microbiome, HPV infection and Torquetenovirus

Men having sex with men (MSM) represent a key population, in which sexually transmitted rectal infections (STIs) caused by Chlamydia trachomatis (CT), Neisseria gonorrhoeae (NG) and high-risk HPV (HR-HPV) are very common and linked to significant morbidity. Investigating the anorectal microbiome associated with rectal STIs holds potential for deeper insights into the pathogenesis of these infections and the development of innovative control strategies. In this study, we explored the interplay at the rectal site between C. trachomatis, N. gonorrhoeae, HR-HPV infection, and the anorectal microbiome in a cohort of 92 MSM (47 infected by CT and/or NG vs 45 controls). Moreover, we assessed the presence of Torquetenovirus (TTV), a non-pathogenic endogenous virus, considered as a possible predictor of immune system activation. We found a high prevalence of HR-HPV rectal infections (61%), especially in subjects with a concurrent CT/NG rectal infection (70.2%) and in people living with HIV (84%). In addition, we observed that TTV was more prevalent in subjects with CT/NG rectal infections than in non-infected ones (70.2% vs 46.7%, respectively). The anorectal microbiome of patients infected by CT and/or NG exhibited a reduction in Escherichia, while the presence of TTV was significantly associated with higher levels of Bacteroides. We observed a positive correlation of HR-HPV types with Escherichia and Corynebacterium, and a negative correlation with the Firmicutes phylum, and with Prevotella, Oscillospira, Sutterella. Our findings shed light on some of the dynamics occurring within the rectal environment involving chlamydial/gonococcal infections, HPV, TTV, and the anorectal microbiome. These data could open new perspectives for the control and prevention of STIs in MSM.

A novel chimeric recombinant FliC-Pgp3 vaccine promotes immunoprotection against Chlamydia muridarum infection in mice

The Pgp3 subunit vaccine elicits immune protection against Chlamydia trachomatis infection, but additional adjuvants are still required to enhance its immunoprotective efficacy. Flagellin can selectively stimulate immunity and act as an adjuvant. In this research, the FliC-Pgp3 recombinant was successfully expressed and purified. Tri-immunization with the FliC-Pgp3 vaccine in Balb/C mice induced rapid and persistent germinal center B-cell response and Tfh differentiation, promoting a significantly higher IgG antibody titer compared to the Pgp3 group. FliC-Pgp3 immunization primarily induced Th1-type cellular immunity, leading to higher levels of IFN-γ, TNF-α, and IL-2 secreted by CD4+ T cells than in Pgp3-vaccinated mice. Chlamydia muridarum challenge results showed that FliC-Pgp3-vaccinated mice exhibited more rapid clearance of Chlamydia muridarum colonization in the lower genital tract, ensuring a lower hydrosalpinx rate and cumulative score. Histological analysis showed reduced dilation and inflammatory infiltration in the oviduct and uterine horn of FliC-Pgp3-vaccinated mice compared to the PBS and Pgp3 control. Importantly, tri-immunization with FliC-Pgp3 effectively activated CD4+ T cells and dendritic cells, as confirmed by the adoptive transfer, resulting in better immune protection in recipient mice. In summary, the novel FliC-Pgp3 chimeric is hoped to be a novel vaccine with improved immunoprotection against Chlamydia muridarum.

Insights into innate immune cell evasion by Chlamydia trachomatis

Chlamydia trachomatis, is a kind of obligate intracellular pathogen. The removal of C. trachomatis relies primarily on specific cellular immunity. It is currently considered that CD4+ Th1 cytokine responses are the major protective immunity against C. trachomatis infection and reinfection rather than CD8+ T cells. The non-specific immunity (innate immunity) also plays an important role in the infection process. To survive inside the cells, the first process that C. trachomatis faces is the innate immune response. As the "sentry" of the body, mast cells attempt to engulf and remove C. trachomatis. Dendritic cells present antigen of C. trachomatis to the "commanders" (T cells) through MHC-I and MHC-II. IFN-γ produced by activated T cells and natural killer cells (NK) further activates macrophages. They form the body's "combat troops" and produce immunity against C. trachomatis in the tissues and blood. In addition, the role of eosinophils, basophils, innate lymphoid cells (ILCs), natural killer T (NKT) cells, γδT cells and B-1 cells should not be underestimated in the infection of C. trachomatis. The protective role of innate immunity is insufficient, and sexually transmitted diseases (STDs) caused by C. trachomatis infections tend to be insidious and recalcitrant. As a consequence, C. trachomatis has developed a unique evasion mechanism that triggers inflammatory immunopathology and acts as a bridge to protective to pathological adaptive immunity. This review focuses on the recent advances in how C. trachomatis evades various innate immune cells, which contributes to vaccine development and our understanding of the pathophysiologic consequences of C. trachomatis infection.

Characteristics of common pathogens of urogenital tract among outpatients in Shanghai, China from 2016 to 2021

Background

Ureaplasma urealyticum, Chlamydia trachomatis, and Neisseria gonorrhoeae are the prevalent causes of several genital diseases worldwide; however, their characteristics in different genders have not been well documented in Shanghai. The aim of this study is to describe the prevalence of common pathogens among outpatients, considering variations by gender and age.

Methods

From January 1, 2016, to December 31, 2021, the urogenital swabs of 16216 outpatients aged 3-95 years from two general hospitals in Shanghai were collected. All participants' swabs were investigated for U. urealyticum, C. trachomatis, and N. gonorrhoeae by isothermal RNA-based simultaneous amplification and testing. The basic information of all participants was also recorded, including age and gender. The chi-square test was used to compare the prevalence between different genders, age groups, and infection patterns.

Results

There were 5,744 patients (35.42%) with positive samples whose ages ranged from 7 to 80 years (33.23 ± 8.63 years), and 62.14% of them were women. The most common pathogen detected was U. urealyticum (85.08%). The highest prevalence rate of all three pathogens was found in patients aged ≤ 20 years (40.53%, 95% confidence intervals [CI]: 33.80%-47.63%). The prevalent rate of U. urealyticum was higher in men (33.36%, 95% CI: 32.19%-34.55%). The overall prevalence rates of U. urealyticum, C. trachomatis, and N. gonorrhoeae were 30.14% (95% CI: 29.44%-30.85%), 6.00% (95% CI: 5.64%-6.38%), and 2.10% (95% CI: 1.89%-2.33%).

Conclusions

Ureaplasma urealyticum was the most prevalent pathogen in the population, and its prevalence decreased with age. Young men aged ≤ 20 years were more frequently infected. Regular screening for sexually transmitted pathogens in different genders and age groups are warranted, particularly in young men.

Lack of neutralization of Chlamydia trachomatis infection by high avidity monoclonal antibodies to surface-exposed major outer membrane protein variable domain IV

Chlamydia trachomatis is the leading cause of sexually transmitted diseases causing frequent, long-lasting, and often asymptomatic recurrent infections resulting in severe reproductive complications. C. trachomatis is an intracellular Gram-negative bacterium with a biphasic developmental cycle in which extracellular, infectious elementary bodies (EB) alternate with the intracellular replicating reticulate bodies (RB). The outer membrane of EB consists of a tight disulfide cross-linking protein network. The most essential protein is the 42 kDa major outer membrane protein (MOMP) that contributes to the rigid structural integrity of the outer membrane. MOMP is a transmembrane protein with a β-barrel structure consisting of four variable domains (VD) separated by five constant domains. VDIV possesses surface-exposed species-specific epitopes recognized by the immune system and, therefore, functions as a candidate for vaccine development. To analyze the protective contribution of antibodies for a MOMP vaccine, we investigated the specificity and binding characteristics of two monoclonal antibodies (MAb)224.2 and MAb244.4 directed against C. trachomatis serovar D MOMP. By immunoelectron microscopy, we found that both MAb bind to the surface of C. trachomatis EB. By epitope mapping, we characterized the MOMP epitope as linear consisting of 6 amino acids: 322TIAGAGD328. By ELISA it was shown that both antibodies bind with a higher avidity to the chlamydial surface compared to binding to monomeric MOMP, indicating that the antibodies bind divalently to the surface of C. trachomatis EB. Despite strong binding to the chlamydial surface, the antibodies only partially reduced the infectivity. This may be explained by the observation that even though both MAb covered the EB surface, antibodies could not be regularly detected on EB after the uptake into the host cell.

Preparation of graphene oxide-stabilized Pickering emulsion adjuvant for Pgp3 recombinant vaccine and enhanced immunoprotection against Chlamydia Trachomatis infection

Background

Traditional emulsion adjuvants are limited in clinical application because of their surfactant dependence. Graphene oxide (GO) has unique amphiphilic properties and therefore has potential to be used as a surfactant substitute to stabilize Pickering emulsions.

Methods

In this study, GO-stabilized Pickering emulsion (GPE) was prepared and used as an adjuvant to facilitate an enhanced immune response to the Chlamydia trachomatis (Ct) Pgp3 recombinant vaccine. Firstly, GPE was prepared by optimizing the sonication conditions, pH, salinity, GO concentration, and water/oil ratio. GPE with small-size droplets was characterized and chosen as the candidate. Subsequently, controlled-release antigen delivery by GPE was explored. Cellular uptake behaviors, M1 polarization, and cytokine stimulation by GPE + Pgp3 was considered in terms of the production of macrophages. Finally, GPE's adjuvant effect was evaluated by vaccination with Pgp3 recombinant in BALB/c mouse models.

Results

GPE with the smallest droplet sizes was prepared by sonication under 163 W for 2 min at 1 mg/mL GO in natural salinity with a pH of 2 when the water/oil ratio was 10:1 (w/w). The optimized average GPE droplet size was 1.8 μm and the zeta potential was -25.0 ± 1.3 mv. GPE delivered antigens by adsorption onto the droplet surface, demonstrating the controlled release of antigens both in vitro and in vivo. In addition, GPE promoted antigen uptake, which stimulated proinflammatory tumor necrosis factor alpha (TNF-α), enhancing the M1 polarization of macrophages in vitro. Macrophage recruitment was also significantly promoted by GPE at the injection site. In the GPE + Pgp3 treatment group, higher levels of immunoglobin (IgG), immunoglobin G1 (IgG1), immunoglobin G2a (IgG2a) sera, and immunoglobin A (IgA) were detected in vaginal fluid, and higher levels of IFN-γ and IL-2 secretion were stimulated, than in the Pgp3 group, showing a significant type 1 T helper (Th1)-type cellular immune response. Chlamydia muridarum challenging showed that GPE enhanced Pgp3's immunoprotection through its advanced clearance of bacterial burden and alleviation of chronic pathological damage in the genital tract.

Conclusion

This study enabled the rational design of small-size GPE, shedding light on antigen adsorption and control release, macrophage uptake, polarization and recruitment, which enhanced augmented humoral and cellular immunity and ameliorated chlamydial-induced tissue damage in the genital tract.

López Font F, A. Zayas Rodríguez F. Persistence in Chlamydia

Chlamydia spp. are important causes of acute and persistent/chronic infections. All Chlamydia spp. display a unique biphasic developmental cycle alternating between an infectious elementary body (EB) and a replicative form, the reticulate body (RB), followed by the multiplication of RBs by binary fission and progressive differentiation back into EBs. During its intracellular life, Chlamydia employs multiple mechanisms to ensure its persistence inside the host. These include evasion of diverse innate immune responses, modulation of host cell structure and endocytosis, inhibition of apoptosis, activation of pro-signaling pathways, and conversion to enlarged, non-replicative but viable “aberrant bodies” (ABs). Early research described several systems for Chlamydial persistence with a significant number of variables that make a direct comparison of results difficult. Now, emerging tools for genetic manipulations in Chlamydia and advances in global microarray, transcriptomics, and proteomics have opened new and exciting opportunities to understand the persistent state of Chlamydia and link the immune and molecular events of persistence with the pathogenesis of recurrent and chronic Chlamydial infections. This chapter reviews our current understanding and advances in the molecular biology of Chlamydia persistence.

Chlamydia trachomatis Cell-to-Cell Spread through Tunneling Nanotubes

Tunneling nanotubes (TNTs) are transient cellular connections that consist of dynamic membrane protrusions. They play an important role in cell-to-cell communication and mediate the intercellular exchanges of molecules and organelles. TNTs can form between different cell types and may contribute to the spread of pathogens by serving as cytoplasmic corridors. We demonstrate that Chlamydia (C.) trachomatis-infected human embryonic kidney (HEK) 293 cells and other cells form TNT-like structures through which reticulate bodies (RBs) pass into uninfected cells. Observed TNTs have a life span of 1 to 5 h and contain microtubules, which are essential for chlamydial transfer. They can bridge distances of up to 50 μm between connecting neighboring cells. Consistent with the biological role for TNTs, we show that C. trachomatis spread also occurs under conditions in which the extracellular route of chlamydial entry into host cells is blocked. Based on our findings, we propose that TNTs play a critical role in the direct, cell-to-cell transmission of chlamydia. IMPORTANCE Intracellular bacterial pathogens often undergo a life cycle in which they parasitize infected host cells in membranous vacuoles. Two pathways have been described by which chlamydia can exit infected host cells: lytic cell destruction or exit via extrusion formation. Whether direct, cell-to-cell contact may also play a role in the spread of infection is unknown. Tunneling nanotubes (TNTs) interconnect the cytoplasm of adjacent cells to mediate efficient communication and the exchange of material between them. We used Chlamydia trachomatis and immortalized cells to analyze whether TNTs mediate bacterial transmission from an infected donor to uninfected acceptor cells. We show that chlamydia-infected cells build TNTs through which the intracellular reticulate bodies (RBs) of the chlamydia can pass into uninfected neighboring cells. Our study contributes to the understanding of the function of TNTs in the cell-to-cell transmission of intracellular pathogens and provides new insights into the strategies by which chlamydia spreads among multicellular tissues.

Therapeutic Options for Chlamydia trachomatis Infection: Present and Future

Sexually transmitted infections (STIs), such as Chlamydia trachomatis (Ct) infection, have serious consequences for sexual and reproductive health worldwide. Ct is one of the most common sexually transmitted bacterial infections in the world, with approximately 129 million new cases per year. C. trachomatis is an obligate intracellular Gram-negative bacterium. The infection is usually asymptomatic, notwithstanding, it could also be associated with severe sequels and complications, such as chronic pain, infertility, and gynecologic cancers, and thus there is an urgent need to adequately treat these cases in a timely manner. Consequently, beyond its individual effects, the infection also impacts the economy of the countries where it is prevalent, generating a need to consider the hypothesis of implementing Chlamydia Screening Programs, a decision that, although it is expensive to execute, is a necessary investment that unequivocally will bring financial and social long-term advantages worldwide. To detect Ct infection, there are different methodologies available. Nucleic acid amplification tests, with their high sensitivity and specificity, are currently the first-line tests for the detection of Ct. When replaced by other detection methods, there are more false negative tests, leading to underreported cases and a subsequent underestimation of Ct infection's prevalence. Ct treatment is based on antibiotic prescription, which is highly associated with drug resistance. Therefore, currently, there have been efforts in line with the development of alternative strategies to effectively treat this infection, using a drug repurposing method, as well as a natural treatment approach. In addition, researchers have also made some progress in the Ct vaccine development over the years, despite the fact that it also necessitates more studies in order to finally establish a vaccination plan. In this review, we have focused on the therapeutic options for treating Ct infection, expert recommendations, and major difficulties, while also exploring the possible avenues through which to face this issue, with novel approaches beyond those proposed by the guidelines of Health Organizations.

Innate Lymphoid Cells in Response to Intracellular Pathogens: Protection Versus Immunopathology

Innate lymphoid cells (ILCs) are a heterogeneous group of cytokine-producing lymphocytes which are predominantly located at mucosal barrier surfaces, such as skin, lungs, and gastrointestinal tract. ILCs contribute to tissue homeostasis, regulate microbiota-derived signals, and protect against mucosal pathogens. ILCs are classified into five major groups by their developmental origin and distinct cytokine production. A recently emerged intriguing feature of ILCs is their ability to alter their phenotype and function in response to changing local environmental cues such as pathogen invasion. Once the pathogen crosses host barriers, ILCs quickly activate cytokine production to limit the spread of the pathogen. However, the dysregulated ILC responses can lead to tissue inflammation and damage. Furthermore, the interplay between ILCs and other immune cell types shapes the outcome of the immune response. Recent studies highlighted the important role of ILCs for host defense against intracellular pathogens. Here, we review recent advances in understanding the mechanisms controlling protective and pathogenic ILC responses to intracellular pathogens. This knowledge can help develop new ILC-targeted strategies to control infectious diseases and immunopathology.

A Survey of Preclinical Studies Evaluating Nanoparticle-Based Vaccines Against Non-Viral Sexually Transmitted Infections

A worldwide estimate of over one million STIs are acquired daily and there is a desperate need for effective preventive as well as therapeutic measures to curtail this global health burden. Vaccines have been the most effective means for the control and potential eradication of infectious diseases; however, the development of vaccines against STIs has been a daunting task requiring extensive research for the development of safe and efficacious formulations. Nanoparticle-based vaccines represent a promising platform as they offer benefits such as targeted antigen presentation and delivery, co-localized antigen-adjuvant combinations for enhanced immunogenicity, and can be designed to be biologically inert. Here we discuss promising types of nanoparticles along with outcomes from nanoparticle-based vaccine preclinical studies against non-viral STIs including chlamydia, syphilis, gonorrhea, and recommendations for future nanoparticle-based vaccines against STIs.

Inhibition of the futalosine pathway for menaquinone biosynthesis suppresses Chlamydia trachomatis infection

Chlamydia trachomatis, an obligate intracellular bacterium with limited metabolic capabilities, possesses the futalosine pathway for menaquinone biosynthesis. Futalosine pathway enzymes have promise as narrow-spectrum antibiotic targets, but the activity and essentiality of chlamydial menaquinone biosynthesis have yet to be established. In this work, menaquinone-7 (MK-7) was identified as a C. trachomatis-produced quinone through liquid chromatography-tandem mass spectrometry. An immunofluorescence-based assay revealed that treatment of C. trachomatis-infected HeLa cells with the futalosine pathway inhibitor docosahexaenoic acid (DHA) reduced inclusion number, inclusion size, and infectious progeny. Supplementation with MK-7 nanoparticles rescued the effect of DHA on inclusion number, indicating that the futalosine pathway is a target of DHA in this system. These results open the door for menaquinone biosynthesis inhibitors to be pursued in antichlamydial development.

Vaginal and Anal Microbiome during Chlamydia trachomatis Infections

Background.Chlamydia trachomatis (CT) is the agent of the most common bacterial sexually transmitted infection worldwide, with a significant impact on women's health. Despite the increasing number of studies about the vaginal microbiome in women with CT infections, information about the composition of the anal microbiome is still lacking. Here, we assessed the bacterial community profiles of vaginal and anal ecosystems associated or not with CT infection in a cohort of Caucasian young women. Methods. A total of 26 women, including 10 with a contemporary vaginal and ano-rectal CT infection, were enrolled. Composition of vaginal and anal microbiome was studied by 16S rRNA gene profiling. Co-occurrence networks of bacterial communities and metagenome metabolic functions were determined. Results. In case of CT infection, both vaginal and anal environments were characterized by a degree of dysbiosis. Indeed, the vaginal microbiome of CT-positive women were depleted in lactobacilli, with a significant increase in dysbiosis-associated bacteria (e.g., Sneathia, Parvimonas, Megasphaera), whereas the anal microbiota of CT-infected women was characterized by higher levels of Parvimonas and Pseudomonas and lower levels of Escherichia. Interestingly, the microbiome of anus and vagina had numerous bacterial taxa in common, reflecting a significant microbial 'sharing' between the two sites. In the vaginal environment, CT positively correlated with Ezakiella spp. while Gardnerella vaginalis co-occurred with several dysbiosis-related microbes, regardless of CT vaginal infection. The vaginal microbiome of CT-positive females exhibited a higher involvement of chorismate and aromatic amino acid biosynthesis, as well as an increase in mixed acid fermentation. Conclusions. These data could be useful to set up new diagnostic/prognostic tools, offering new perspectives for the control of chlamydial infections.

Is Chlamydia to Blame for Koala Reproductive Cysts?

A significant threat to koala populations is infection from Chlamydia, which results in disease and death. Wild koalas with Chlamydia infections are admitted to wildlife hospitals and treated with antibiotics; however, up to 50% of koalas that present to wildlife hospitals do not survive. A major contributor to high mortality is the development of reproductive cysts, resulting in female infertility and euthanasia. However, the diagnosis of reproductive disease is limited to ultrasound with no further investigations. This communication highlights reports of histological and microbiological findings, the accuracy of ultrasound to necropsy reports and other possible causes for reproductive cyst development previously reported in other hosts. Our conclusions identify a significant knowledge gap in the aetiology of koala reproductive cysts and highlight the urgent need for future investigations.

Chlamydia trachomatis: Cell biology, immunology and vaccination

Chlamydia trachomatis is the causative agent of a highly prevalent sexually transmitted bacterial disease and is associated with a number of severe disease complications. Current therapy options are successful at treating disease, but patients are left without protective immunity and do not benefit the majority asymptomatic patients who do not seek treatment. As such, there is a clear need for a broad acting, protective vaccine that can prevent transmission and protect against symptomatic disease presentation. There are three key elements that underlie successful vaccine development: 1) Chlamydia biology and immune-evasion adaptations, 2) the correlates of protection that prevent disease in natural and experimental infection, 3) reflection upon the evidence provided by previous vaccine attempts. In this review, we give an overview of the unique intra-cellular biology of C. trachomatis and give insight into the dynamic combination of adaptations that allow Chlamydia to subvert host immunity and survive within the cell. We explore the current understanding of chlamydial immunity in animal models and in humans and characterise the key immune correlates of protection against infection. We discuss in detail the specific immune interactions involved in protection, with relevance placed on the CD4+ T lymphocyte and B lymphocyte responses that are key to pathogen clearance. Finally, we provide a timeline of C. trachomatis vaccine research to date and evaluate the successes and failures in development so far. With insight from these three key elements of research, we suggest potential solutions for chlamydial vaccine development and promising avenues for further exploration.

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

Simple Summary

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

Abstract

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

Impact of Helminth Infections on Female Reproductive Health and Associated Diseases

A growing body of knowledge exists on the influence of helminth infections on allergies and unrelated infections in the lung and gastrointestinal (GI) mucosa. However, the bystander effects of helminth infections on the female genital mucosa and reproductive health is understudied but important considering the high prevalence of helminth exposure and sexually transmitted infections in low- and middle-income countries (LMICs). In this review, we explore current knowledge about the direct and systemic effects of helminth infections on unrelated diseases. We summarize host disease-controlling immunity of important sexually transmitted infections and introduce the limited knowledge of how helminths infections directly cause pathology to female reproductive tract (FRT), alter susceptibility to sexually transmitted infections and reproduction. We also review work by others on type 2 immunity in the FRT and hypothesize how these insights may guide future work to help understand how helminths alter FRT health.

Extraction and bioinformatics analysis of Chlamydia trachomatis LpxA

OBJECTIVE

The aim of this study is to clone the LpxA gene of Chlamydia trachomatis and analyze its biological characteristics.

METHODS

Specific primers were designed according to the sequence of Ct LpxA gene. LpxA gene was amplified by PCR and connected to pMD18-T vectors. Positive clones were selected for PCR and DNA sequencing. Finally, bioinformatics software was used to analyze the biological properties of LpxA protein.

RESULTS

The total length of LpxA gene was 840 bp, encoding 280 amino acids. LpxA protein has no signal peptide and was located in bacterial cytoplasm. The prediction of secondary structure showed that the α-helix, extended strand, β-turn and random coil accounted for 19.6%, 32.8%, 11.4% and 36%, respectively. According to the prediction of tertiary structure, three identical LpxA molecules constituted homologous trimers. It was predicted that there were 11 B cell epitopes in LpxA.

CONCLUSION

Ct Lpxa gene was cloned, and LpxA protein structure and function were predicted.

Coxiella burnetii-Infected NK Cells Release Infectious Bacteria by Degranulation

Natural killer (NK) cells are critically involved in the early immune response against various intracellular pathogens, including Coxiella burnetii and Chlamydia psittaci Chlamydia-infected NK cells functionally mature, induce cellular immunity, and protect themselves by killing the bacteria in secreted granules. Here, we report that infected NK cells do not allow intracellular multiday growth of Coxiella, as is usually observed in other host cell types. C. burnetii-infected NK cells display maturation and gamma interferon (IFN-γ) secretion, as well as the release of Coxiella-containing lytic granules. Thus, NK cells possess a potent program to restrain and expel different types of invading bacteria via degranulation. Strikingly, though, in contrast to Chlamydia, expulsed Coxiella organisms largely retain their infectivity and, hence, escape the cell-autonomous self-defense mechanism in NK cells.

Capturing Complex Vaccine-Immune-Disease Relationships for Free-Ranging Koalas: Higher Chlamydial Loads Are Associated With Less IL17 Expression and More Chlamydial Disease

Background: Chlamydial disease is a major factor negatively affecting koala populations. Vaccination is a promising management option that would result in immune-mediated protection against disease. Measuring and assessing vaccine efficacy can be challenging owing to both direct and indirect interactions caused by vaccination. In this study, we investigate vaccine-immune-chlamydial load-disease relationships from MOMP (major outer membrane protein) vaccine trials to protect healthy free-ranging koalas against Chlamydia-related diseases. Methods: We created a priori hypotheses based on data sources and perceived direct and indirect interactions from koalas vaccinated 6 months prior. Each hypothesis was tested as a structural equation model separately for either the urogenital or the ocular site to evaluate possible causality among measured variables. Model averaging was used as multiple models fit the data, and the strength of relationships was examined through averaged coefficients and the raw data. Results: We found more relationships in urogenital models as compared to ocular models, particularly those with interleukin 17 (IL17) mRNA expression compared to models with interferon gamma (IFNγ) expression. In the averaged model with IL17, urogenital chlamydial load was positively associated with disease and negatively associated with IL17 expression. MOMP vaccination had a trending effect for reducing urogenital chlamydial load and also had a strong effect on increasing IL17 expression. Not surprisingly, urogenital chlamydial load was a positive predictor for the development of urogenital disease at 6 months post-vaccination. Conclusions: Despite multiple potential sources of variation owing to the koalas in this study being free-ranging, our analyses provide unique insights into the effects of vaccinating against Chlamydia. Using structural equation modeling, this study has helped illuminate that the expression of the immune cytokine IL17 is linked to MOMP vaccination, and animals with a high urogenital chlamydial load expressed less IL17 and were more likely to develop disease, enhancing previous investigations. Going beyond univariate statistics, the methods used in this study can be applied to other preclinical vaccination experiments to identify important direct and indirect factors underpinning the effects of a vaccine.

Human Fallopian Tube Epithelial Cell Culture Model To Study Host Responses to Chlamydia trachomatis Infection

Chlamydia trachomatis infection of the human fallopian tubes can lead to damaging inflammation and scarring, ultimately resulting in infertility. To study the human cellular responses to chlamydial infection, researchers have frequently used transformed cell lines that can have limited translational relevance. We developed a primary human fallopian tube epithelial cell model based on a method previously established for culture of primary human bronchial epithelial cells. After protease digestion and physical dissociation of excised fallopian tubes, epithelial cell precursors were expanded in growth factor-containing medium. Expanded cells were cryopreserved to generate a biobank of cells from multiple donors and cultured at an air-liquid interface. Culture conditions stimulated cellular differentiation into polarized mucin-secreting and multiciliated cells, recapitulating the architecture of human fallopian tube epithelium. The polarized and differentiated cells were infected with a clinical isolate of C. trachomatis, and inclusions containing chlamydial developmental forms were visualized by fluorescence and electron microscopy. Apical secretions from infected cells contained increased amounts of proteins associated with chlamydial growth and replication, including transferrin receptor protein 1, the amino acid transporters SLC3A2 and SLC1A5, and the T-cell chemoattractants CXCL10, CXCL11, and RANTES. Flow cytometry revealed that chlamydial infection induced cell surface expression of T-cell homing and activation proteins, including ICAM-1, VCAM-1, HLA class I and II, and interferon gamma receptor. This human fallopian tube epithelial cell culture model is an important tool with translational potential for studying cellular responses to Chlamydia and other sexually transmitted pathogens.

Effect of Chlamydia trachomatis on adverse pregnancy outcomes: a meta-analysis

PURPOSE

To analyze the effect of Chlamydia trachomatis (C. trachomatis) on adverse pregnancy outcomes based on the currently available evidence.

METHODS

Multiple databases were comprehensively searched from the available date of inception through December 9, 2019. The effect of C. trachomatis on adverse pregnancy outcomes was assessed using pooled odds rations (ORs) and 95% confidence intervals (CIs). Egger's test was used for publication bias.

RESULTS

Fifty studies involving 502,141 participants were identified. C. trachomatis infection was found to be associated with preterm birth in antibody detection [OR (95% CI): 1.571 (1.112-2.220), P = 0.010] and high-quality assessment [OR (95% CI): 1.734 (1.295-2.321), P < 0.001], preterm premature rupture of membranes (PPROM) in culture detection [OR (95% CI): 4.339 (1.806-10.424), P = 0.001] and high-quality assessment [OR (95% CI): 2.822 (1.333-5.973), P = 0.007], stillbirth [OR (95% CI): 1.585 (1.219-2.062), P = 0.001], low-birthweight babies [OR (95% CI): 2.205 (1.137-4.274), P = 0.019], and babies small for gestational age [OR (95% CI): 1.193 (1.091-1.305), P < 0.001]. No publication bias was exhibited in miscarriage (P = 0.170), preterm birth (P = 0.303), PPROM (P = 0.341), stillbirth (P = 0.533), and low-birthweight babies (P = 0.535).

CONCLUSIONS

C. trachomatis infection during pregnancy is associated with a higher risk of preterm birth, PPROM, stillbirth, low-birthweight babies, and babies small for gestational age.

Chlamydia trachomatis Is Associated With Medically Indicated Preterm Birth and Preeclampsia in Young Pregnant Women

BACKGROUND

Studies on Chlamydia trachomatis-associated pregnancy outcomes are largely conflicting, ignoring the heterogeneous natures of pregnancy complications and potential effect modification by maternal age. This study determined if prenatal C. trachomatis infection is associated with preterm birth (PTB) and preeclampsia subtypes.

METHODS

A retrospective cohort study was conducted using 22,772 singleton pregnancies with a prenatal C. trachomatis diagnostic test. Spontaneous and medically indicated PTBs, and term and preterm preeclampsia were outcomes. Modified Poisson regression calculated relative risk (RR) and 95% confidence intervals (CI) with propensity score adjustments stratified by maternal ages <25 and ≥25 years.

RESULTS

Overall, C. trachomatis was significantly associated with term preeclampsia (adjusted RR [RRadj], 1.88; 95% CI, 1.38-2.57). Among young women (age <25 years), C. trachomatis was significantly associated with medically indicated PTB (RRadj, 2.29; 95% CI, 1.38-3.78) and term preeclampsia (RRadj, 1.57; 95% CI, 1.05-2.36) in propensity-adjusted models. No significant associations in older women were detected.

CONCLUSION

C. trachomatis was associated with medically indicated PTB and term preeclampsia in young women. Associations between chlamydia and perinatal outcomes may depend on the subtype of PTB and preeclampsia, which should be investigated through mechanistic studies.

Semi-CAM: A semi-supervised deconvolution method for bulk transcriptomic data with partial marker gene information

Deconvolution of bulk transcriptomics data from mixed cell populations is vital to identify the cellular mechanism of complex diseases. Existing deconvolution approaches can be divided into two major groups: supervised and unsupervised methods. Supervised deconvolution methods use cell type-specific prior information including cell proportions, reference cell type-specific gene signatures, or marker genes for each cell type, which may not be available in practice. Unsupervised methods, such as non-negative matrix factorization (NMF) and Convex Analysis of Mixtures (CAM), in contrast, completely disregard prior information and thus are not efficient for data with partial cell type-specific information. In this paper, we propose a semi-supervised deconvolution method, semi-CAM, that extends CAM by utilizing marker information from partial cell types. Analysis of simulation and two benchmark data have demonstrated that semi-CAM outperforms CAM by yielding more accurate cell proportion estimations when markers from partial/all cell types are available. In addition, when markers from all cell types are available, semi-CAM achieves better or similar accuracy compared to the supervised method using signature genes, CIBERSORT, and the marker-based supervised methods semi-NMF and DSA. Furthermore, analysis of human chlamydia-infection data with bulk expression profiles from six cell types and prior marker information of only three cell types suggests that semi-CAM achieves more accurate cell proportion estimations than CAM.

Protection of outbred mice against a vaginal challenge by a Chlamydia trachomatis serovar E recombinant major outer membrane protein vaccine is dependent on phosphate substitution in the adjuvant

Chlamydia trachomatis is the most common bacterial sexually-transmitted pathogen for which there is no vaccine. We previously demonstrated that the degree of phosphate substitution in an aluminum hydroxide adjuvant in a TLR-4-based C. trachomatis serovar E (Ser E) recombinant major outer membrane protein (rMOMP) formulation had an impact on the induced antibody titers and IFN-γ levels. Here, we have extended these observations using outbreed CD-1 mice immunized with C. trachomatis Ser E rMOMP formulations to evaluate the impact on bacterial challenge. The results confirmed that the rMOMP vaccine containing the adjuvant with the highest phosphate substitution induced the highest neutralizing antibody titers while the formulation with the lowest phosphate substitution induced the highest IFN-γ production. The most robust protection was observed in mice vaccinated with the formulation containing the adjuvant with the lowest phosphate substitution, as shown by the number of mice with positive vaginal cultures, number of positive cultures and number of C. trachomatis inclusion forming units recovered. This is the first report showing that vaccination of an outbred strain of mice with rMOMP induces protection against a vaginal challenge with C. trachomatis.

Navigating to the most promising directions amid complex fields of vaccine development: a chlamydial case study

Background: Vaccine-development research is proliferating making it difficult to determine the most promising vaccine candidates. Exemplary of this problem is vaccine development against Chlamydia, a pathogen of global public health and financial importance.Methods: We systematically extracted data from studies that included chlamydial load or host immune parameter measurements, estimating 4,453 standardized effect sizes between control and chlamydial immunization experimental groups.Results: Chlamydial immunization studies most often used (78%) laboratory mouse models. Depending on chlamydial species, single and multiple recombinant protein, viral and bacterial vectors, dendritic transfer, and dead whole pathogen were most effective at reducing chlamydial load. Immunization-driven decrease in chlamydial load was associated with increases in IFNg, IgA, IgG1, and IgG2a. Using data from individual studies, the magnitude of IgA and IgG2a increase was correlated with chlamydial load reduction. IFNg also showed this pattern for C. trachomatis, but not for C. muridarum. We also reveal the chlamydial vaccine development field to be highly bias toward studies showing these effects, limiting lessons learned from negative results.Conclusions: Most murine immunizations against Chlamydia reduced chlamydial load and increased host immune parameters. These methods are novel for vaccine development and are critical in identifying trends where large quantities of literature exist.

Rectal Microbiota Associated With Chlamydia trachomatis and Neisseria gonorrhoeae Infections in Men Having Sex With Other Men

Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (NG) represent the most common agents of sexually transmitted rectal infections among men having sex with other men (MSM). In this study, we assessed the bacterial composition of the rectal microbiota associated with CT and/or NG infections in a cohort of men reporting unsafe rectal intercourse. A total of 125 rectal swabs were collected and four groups were compared: non-infected subjects (n = 53), patients with CT (n = 37), or NG rectal infection (n = 17) and patients with contemporary positivity for CT/NG (n = 18). CT and NG infections were detected by a real-time commercial test and the rectal microbiota composition was analyzed from rectal swabs through sequencing of the hypervariable V3-V4 regions of the 16S rRNA gene. The rectal microbiota of all subgroups was dominated by Prevotellaceae, Enterobacteriaceae, and Ruminococcaceae families. Irrespective of the analyzed subgroup, we found that the rectal environment of all the enrolled MSM was rich in Prevotella and Escherichia genera. Moreover, a shift in the bacterial composition between patients with sexually transmitted rectal infections and controls was noticed: infected patients were characterized by a depletion of Escherichia species, associated with an increase of anaerobic genera, including Peptoniphilus, Peptostreptococcus, and Parvimonas. Overall, the presence of rectal symptoms did not significantly modify the rectal microbiota profiles among the four groups of analyzed patients. We confirmed that HIV-positive patients are characterized by a lower bacterial richness than HIV-negative subjects. However, we found that the presence of HIV has a different impact on bacterial rectal communities compared to CT and NG infections, modifying the relative abundance of several genera, including Gardnerella, Lactobacillus, Corynebacterium, and Sutterella. Information about the rectal microbiota composition in CT and NG infections could shed light on the pathogenesis of these conditions and could contribute to the onset of new strategies for their control.

Mechanisms of sexually transmitted infection-induced inflammation in women: implications for HIV risk

INTRODUCTION

Globally, sexually transmitted infections (STI) affect >300 million people annually, and are a major cause of sexual and reproductive health complications in women. In this commentary, we describe how STIs interact with the immune and non-immune cells, both within and below the cervicovaginal mucosal barrier, to cause inflammation, which in turn has been associated with increased HIV acquisition risk.

DISCUSSION

STIs have a major impact on the female genital mucosa, which is an important biological and physical barrier that forms the first line of defence against invading microorganisms such as HIV. Pattern recognition of STI pathogens, by receptors expressed either on the cell surface or inside the cell, typically triggers inflammation at the mucosal barrier. The types of mucosal responses vary by STI, and can be asymptomatic or culminate in the formation of discharge, ulcers and/or warts. While the aim of this response is to clear the invading microbes, in many cases these responses are either evaded or cause pathology that impairs barrier integrity and increases HIV access to target cells in the sub-mucosa. In addition, innate responses to STIs can result in an increased number of immune cells, including those that are the primary targets of HIV, and may contribute to the association between STIs and increased susceptibility to HIV acquisition. Many of these cells are mediators of adaptive immunity, including tissue-resident cells that may also display innate-like functions. Bacterial vaginosis (BV) is another common cause of inflammation, and evidence for multiple interactions between BV, STIs and HIV suggest that susceptibility to these conditions should be considered in concert.

CONCLUSIONS

STIs and other microbes can induce inflammation in the genital tract, perturbing the normal robust function of the mucosal barrier against HIV. While the impact of STIs on the mucosal immune system and HIV acquisition is often under-appreciated, understanding their interactions of the infections with the immune responses play an important role in improving treatment and reducing the risk of HIV acquisition. The frequent sub-clinical inflammation associated with STIs underscores the need for better STI diagnostics to reverse the immunological consequences of infection.

NK Cell-Mediated Processing Of Chlamydia psittaci Drives Potent Anti-Bacterial Th1 Immunity

Natural killer (NK) cells are innate immune cells critically involved in the early immune response against various pathogens including chlamydia. Here, we demonstrate that chlamydia-infected NK cells prevent the intracellular establishment and growth of the bacteria. Upon infection, they display functional maturation characterized by enhanced IFN-γ secretion, CD146 induction, PKCϴ activation, and granule secretion. Eventually, chlamydia are released in a non-infectious, highly immunogenic form driving a potent Th1 immune response. Further, anti-chlamydial antibodies generated during immunization neutralize the infection of epithelial cells. The release of chlamydia from NK cells requires PKCϴ function and active degranulation, while granule-associated granzyme B drives the loss of chlamydial infectivity. Cellular infection and bacterial release can be undergone repeatedly and do not affect NK cell function. Strikingly, NK cells passing through such an infection cycle significantly improve their cytotoxicity. Thus, NK cells not only protect themselves against productive chlamydial infections but also actively trigger potent anti-bacterial responses.

IL-10 Producing B Cells Dampen Protective T Cell Response and Allow Chlamydia muridarum Infection of the Male Genital Tract

A significant proportion of individuals develop chronic, persistent and recurrent genital tract infections with Chlamydia trachomatis, which has been attributed to the numerous strategies that the bacterium uses to subvert host immune responses. Animal chlamydia models have demonstrated that protective immune response is mediated by CD4⁺ Th1 cytokine responses. Herein, we demonstrate that early after infecting the male genital tract, C. muridarum triggers the production of IL-10 by splenic and lymph node cells. In addition, C. muridarum triggers IL-6 and TNFα secretion. Data obtained from in vitro and in vivo experiments revealed B cells as the major IL-10 contributors. Indeed, purified B cells produced high amounts of IL-10 and also exhibited enhanced expression of inhibitory molecules such as CD39, PD-L1 and PD1 after C. muridarum stimulation. In vitro experiments performed with sorted cell subsets revealed that Marginal Zone B cells were the main IL-10 producers. In vitro and in vivo studies using TLR-deficient mice indicated that TLR4 signaling pathway was essential for IL-10 production. In addition, in vivo treatments to neutralize IL-10 or deplete B cells indicated that IL-10 and B cells played a significant role in delaying bacterial clearance ability. Moreover, the latter was confirmed by adoptive cell transfer experiments in which the absence of IL-10-producing B cells conferred the host a greater capability to induce Th1 responses and clear the infection. Interestingly, NOD mice, which were the least efficient in clearing the infection, presented much more Marginal Zone B counts and also enhanced TLR4 expression on Marginal Zone B cells when compared to B6 and BALB/c mice. Besides, treatment with antibodies that selectively deplete Marginal Zone B cells rendered mice more capable of inducing enhanced IFNγ responses and clearing the infection. Our findings suggest that B cells play a detrimental role in C. muridarum infection and that activation by innate receptors like TLR4 and IL-10 production by these cells could be used by Chlamydia spp. as a strategy to modulate the immune response establishing chronic infections in susceptible hosts.

Seventy Years of Chlamydia Vaccine Research - Limitations of the Past and Directions for the Future

Chlamydia is a major bacterial pathogen that infects humans, as well as a wide range of animals, including marsupials, birds, cats, pigs, cattle, and sheep. Antibiotics are the only treatment currently available, however, with high rates of re-infection, there is mounting pressure to develop Chlamydia vaccines. In this review, we analyzed how Chlamydia vaccine trials have developed over the past 70 years and identified where future trials need to be focused. There has been a strong bias toward studies targeting C. muridarum and C. trachomatis within mice and a lack of studies matching chlamydial species to their end target host. Even though a large number of specific antigenic targets have been studied, the results from whole-cell vaccine targets show slightly more promising results overall. There has also been a strong bias toward systemic vaccine delivery systems, despite the finding that mucosal delivery systems have shown more promising outcomes. However, the only successful vaccines with matched chlamydial species/infecting host are based on systemic vaccine delivery methods. We highlight the extensive work done with mouse model trials and indicate that whole cell antigenic targets are capable of inducing an effective response, protecting from disease and reducing shedding rates. However, replication of these results using antigen preparations more conducive to commercial vaccine production has proven difficult. To date, the Major Outer Membrane Protein (MOMP) has emerged as the most suitable substitute for whole cell targets and its delivery as a combined systemic and mucosal vaccine is most effective. Finally, although mouse model trials are useful, differences between hosts and infecting chlamydial strains are preventing vaccine formulations from mouse models to be translated into larger animals or intended hosts.

Waddlia chondrophila, a Chlamydia-related bacterium, has a negative impact on human spermatozoa

STUDY QUESTION

What is the impact of Waddlia chondrophila, an emerging Chlamydia-related bacterium associated with miscarriage, on human spermatozoa?

SUMMARY ANSWER

W. chondrophila had a negative impact on human spermatozoa (decrease in viability and mitochondrial membrane potential) and was not entirely removed from infected samples by density gradient centrifugation.

WHAT IS KNOWN ALREADY

Bacterial infection or colonization might have a deleterious effect on male fertility. Waddlia chondrophila was previously associated with miscarriage, but its impact on male reproductive function has never been studied.

STUDY DESIGN SIZE, DURATION

An in vitro model of human spermatozoa infection was used to assess the effects of W. chondrophila infection. Controls included Chlamydia trachomatis serovar D and latex beads with similar size to bacteria.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Purified motile spermatozoa were infected with W. chondrophila (multiplicity of infection of 1). Immunohistochemistry combined with confocal microscopy was used to evaluate how bacteria interact with spermatozoa. The impact on physiology was assessed by monitoring cell viability, mitochondrial membrane potential and DNA fragmentation.

MAIN RESULTS AND THE ROLE OF CHANCE

Using super-resolution confocal microscopy, bacteria were localized on spermatozoa surface, as well as inside the cytoplasm. Compared to controls, W. chondrophila caused a 20% increase in mortality over 72 h of incubation (P < 0.05). Moreover, higher bacterial loads significantly reduced mitochondrial membrane potential. Bacteria present on spermatozoa surface were able to further infect a cell-monolayer, indicating that sperm might vector bacteria during sexual intercourse.

LIMITATIONS REASONS FOR CAUTION

The main limitation of the study is the use of an in vitro model of infection, which might be too simplistic compared to an actual infection. An animal model of infection should be developed to better evaluate the in vivo impact of W. chondrophila.

WIDER IMPLICATIONS OF THE FINDINGS

Intracellular bacteria, including C. trachomatis, Mycoplasma spp. and Ureaplasma spp., are associated with male infertility. Waddlia chondrophila might represent yet another member of this group, highlighting the need for more rigorous microbiological analysis during investigations for male infertility.

STUDY FUNDING/COMPETING INTEREST(S)

This work has been funded by the Department of Obstetrics and Gynecology, Lausanne University Hospital, Switzerland, and by the Swiss National Science Foundation (Grant nos. 310030-156169/1, 320030-169853/1 and 320030-169853/2 attributed to D.B.). D.B. is also supported by the 'Fondation Leenaards' through the 'Bourse pour la relève académique', by the 'Fondation Divesa' and by the 'Loterie Romande'. No conflicts of interest to declare.

Chinese Herbal Formula Feilin Vaginal Gel Prevents the Cervicitis in Mouse Model

Cervicitis is a common sexually transmitted disease. In recent years, the abuse of antibiotic in the treatment of cervicitis results in the emergence of antibiotic-resistant bacteria; alternative strategies are needed to be developed. In this research, we investigated the effects of Feilin Vaginal Gel (FVG), a Chinese herbal formula, on the treatment of cervicitis. Two cervicitis models were optimized using BALB/c mouse; one in vitro model was established in HeLa cells. In Chlamydia trachomatis-induced cervicitis model, the high level of bacterial loads, the inflammation in tissue, and the cytokines in serum could be observed. With the administration of FVG, the bacterial loads in cervical mucus and cervix tissue could be significantly inhibited in dose-dependent manners. The pathological injury of cervix and vagina, as well as the levels of IL-2, IL-17, and MCP-1 in serum, could be mitigated by FVG. FVG reduced the number of inclusion induced by C. trachomatis in HeLa cells. In addition, the histological damage in Escherichia coli and Staphylococcus aureus-induced cervicitis model could be reduced by FVG. These results suggest that FVG is capable of treating cervicitis through the inhibition of pathogens and the regulation of host immune responses. FVG may contribute as an alternative agent for the treatment of cervicitis.

Therapeutic effect of a Chlamydia pecorum recombinant major outer membrane protein vaccine on ocular disease in koalas (Phascolarctos cinereus)

Chlamydia pecorum is responsible for causing ocular infection and disease which can lead to blindness in koalas (Phascolarctos cinereus). Antibiotics are the current treatment for chlamydial infection and disease in koalas, however, they can be detrimental for the koala’s gastrointestinal tract microbiota and in severe cases, can lead to dysbiosis and death. In this study, we evaluated the therapeutic effects provided by a recombinant chlamydial major outer membrane protein (MOMP) vaccine on ocular disease in koalas. Koalas with ocular disease (unilateral or bilateral) were vaccinated and assessed for six weeks, evaluating any changes to the conjunctival tissue and discharge. Samples were collected pre- and post-vaccination to evaluate both humoral and cell-mediated immune responses. We further assessed the infecting C. pecorum genotype, host MHC class II alleles and presence of koala retrovirus type (KoRV-B). Our results clearly showed an improvement in the clinical ocular disease state of all seven koalas, post-vaccination. We observed increases in ocular mucosal IgA antibodies to whole C. pecorum elementary bodies, post-vaccination. We found that systemic cell-mediated immune responses to interferon-γ, interleukin-6 and interleukin-17A were not significantly predictive of ocular disease in koalas. Interestingly, one koala did not have as positive a clinical response (in one eye primarily) and this koala was infected with a C. pecorum genotype (E’) that was not used as part of the vaccine formula (MOMP genotypes A, F and G). The predominant MHC class II alleles identified were DAb*19, DAb*21 and DBb*05, with no two koalas identified with the same genetic sequence. Additionally, KoRV-B, which is associated with chlamydial disease outcome, was identified in two (29%) ocular diseased koalas, which still produced vaccine-induced immune responses and clinical ocular improvements post-vaccination. Our findings show promise for the use of a recombinant chlamydial MOMP vaccine for the therapeutic treatment of ocular disease in koalas.

Prevalence of Ureaplasma urealyticum, Chlamydia trachomatis, Neisseria gonorrhoeae and herpes simplex virus in Beijing, China

The prevalence of sexually transmitted infection (STI) pathogens in Beijing, China, is rarely reported. In this study, 34 911 symptomatic outpatients with suspected genital infections who attended outpatient clinics in a tertiary care hospital were included to investigate the updated prevalence of Ureaplasma urealyticum (UU), Chlamydia trachomatis (CT), Neisseria gonorrhoeae (NG) and herpes simplex virus (HSV) from 1 January 2013 to 31 December 2016 in Beijing, China. Results indicated that a decrease trend (UU, CT, NG and HSV) in male and an increase trend (UU, CT and NG) in female were observed during the period. Patients aged 20–39 years old were mostly affected by these pathogens, while the prevalence in patients aged 20–29 years old was the highest, The prevalence of UU in male was significantly lower than in female (31.5% vs. 49.3%, P < 0.05), while the prevalence of NG in male was significantly higher than in female (2.5% vs. 0.8%, P < 0.05). In patients with co-infections, 60.6% of male and 71.4% of female were co-infected by UU + CT. In total, 11.9% and 88.1% of patients with HSV infections were confirmed to be infected by HSV-1 and HSV-2. This study could contribute to a better understanding of the current epidemiological features of UU, NG, CT and HSV among symptomatic patients attending an outpatient clinic in Beijing, China, and thus facilitate to develop more effective intervention, prevention and treatment of STI.

An Organotypic Reconstructed Human Urethra to Study Chlamydia trachomatis Infection

Organotypic models to investigate host-microbiome interactions are still a challenge for the field of tissue engineering. This is particularly the case for organs such as the urethra. Several cell line, animal, and tissue models are available to study Chlamydia trachomatis infections, but none fully reflects natural infection in native human tissue. Therefore, we developed an organotypic reconstructed human urethral model (RhU) to study invasive and noninvasive strains of C. trachomatis. Primary urethra cells were used to reconstruct epithelium on a fibroblast populated collagen-fibrin hydrogel, yielding a RhU. Immunohistochemistry was used to compare RhU with native urethral tissue and to visualize the location of C. trachomatis bacteria in RhU after 10-day exposure. RhU closely resembled native urethral tissue with respect to proliferation and differentiation markers (keratins 6, 10, 13, 17, involucrin, SKALP [skin-derived antileucoproteinase], vimentin, and CD31). Exposure of RhU to noninvasive and invasive C. trachomatis strains revealed relevant differences in infection ability because inclusions were observed (indicating active infection) in the epithelial layer after 10 days exposure only to the invasive strain. The noninvasive strain remained localized on the surface of the epithelial layer. Human primary urethral fibroblasts and keratinocytes can be used to construct RhU that closely resembles native tissue and can be used to investigate active C. trachomatis infections. RhU provides a promising model to investigate host-microbiome interactions such as, but not limited to, the human pathogenesis of C. trachomatis.

Complement C3 opsonization of Chlamydia trachomatis facilitates uptake in human monocytes

Chlamydia trachomatis is an obligate intracellular bacterium that causes severe infections, which can lead to infertility and ectopic pregnancy. Although both innate and adaptive immune responses are elicited during chlamydial infection the bacterium succeeds to evade host defense mechanisms establishing chronic infections. Thus, studying the host-pathogen interaction during chlamydial infection is of importance to understand how C. trachomatis can cause chronic infections. Both the complement system and monocytes play essential roles in anti-bacterial defense, and, therefore, we investigated the interaction between the complement system and the human pathogens C. trachomatis D and L2. Complement competent serum facilitated rapid uptake of both chlamydial serovars into monocytes. Using immunoelectron microscopy, we showed that products of complement C3 were loosely deposited on the bacterial surface in complement competent serum and further characterization demonstrated that the deposited C3 product was the opsonin iC3b. Using C3-depleted serum we confirmed that complement C3 facilitates rapid uptake of chlamydiae into monocytes in complement competent serum. Complement facilitated uptake did not influence intracellular survival of C. trachomatis or C. trachomatis-induced cytokine secretion. Hence, C. trachomatis D and L2 activate the complement system leading to chlamydial opsonization by iC3b and subsequent phagocytosis, activation and bacterial elimination by human monocytes.

Koala immunology and infectious diseases: How much can the koala bear?

Infectious diseases are contributing to the decline of the iconic Australian marsupial, the koala (Phascolarctos cinereus). Infections with the obligate intracellular bacteria, Chlamydia pecorum, cause debilitating ocular and urogenital-tract disease while the koala-retrovirus (KoRV) has been implicated in host immunosuppression and exacerbation of chlamydial pathogenesis. Although histological studies have provided insight into the basic architecture of koala immune tissues, our understanding of the koala immune response to infectious disease has been limited, until recently, by a lack of species-specific immune reagents. Recent advances in the characterisation of key immune genes have focused on advancing our understanding of the immune response to Chlamydia infection, revealing commonalities in disease pathologies and immunity between koalas and other hosts and paving the way for the development of a koala Chlamydia vaccine. This review summarises these recent findings and highlights key aspects of the koala immune system requiring further attention with particular regard to their most prominent infectious diseases.

Caveolin-mediated endocytosis of the Chlamydia M278 outer membrane peptide encapsulated in poly(lactic acid)-Poly(ethylene glycol) nanoparticles by mouse primary dendritic cells enhances specific immune effectors mediated by MHC class II and CD4+ T cells

We previously developed a Chlamydia trachomatis nanovaccine (PPM) by encapsulating a chlamydial M278 peptide within poly(lactic acid)-poly(ethylene glycol) biodegradable nanoparticles that immunopotentiated Chlamydia-specific immune effector responses in mice. Herein, we investigated the mechanistic interactions of PPM with mouse bone marrow-derived dendritic cells (DCs) for its uptake, trafficking, and T cell activation. Our results reveal that PPM triggered enhanced expression of effector cytokines and chemokines, surface activation markers (Cd1d2, Fcgr1), pathogen-sensing receptors (TLR2, Nod1), co-stimulatory (CD40, CD80, CD86) and MHC class I and II molecules. Co-culturing of PPM-primed DCs with T cells from C. muridarum vaccinated mice yielded an increase in Chlamydia-specific immune effector responses including CD3+ lymphoproliferation, CD3+CD4+ IFN-γ-secreting cells along with CD3+CD4+ memory (CD44high and CD62Lhigh) and effector (CD44high and CD62Llow) phenotypes. Intracellular trafficking analyses revealed an intense expression and colocalization of PPM predominantly in endosomes. PPM also upregulated the transcriptional and protein expression of the endocytic mediator, caveolin-1 in DCs. More importantly, the specific inhibition of caveolin-1 led to decreased expression of PPM-induced cytokines and co-stimulatory molecules. Our investigation shows that PPM provided enhancement of uptake, probably by exploiting the caveolin-mediated endocytosis pathway, endosomal processing, and MHC II presentation to immunopotentiate Chlamydia-specific immune effector responses mediated by CD4+ T cells.

Soybean oil containing ginseng saponins as adjuvants promotes production of cytokines and enhances immune responses to foot-and-mouth disease vaccine

In the present study, the adjuvant effect of soybean oil containing ginseng root saponins (SO-GS-R) on the immune response to foot-and-mouth disease vaccine (FMDV) in mice was investigated. When immunized with FMDV antigen emulsified in an SO-GS-R formulation, mice generated remarkably higher serum antibody and cytokine responses than mice immunized with FMDV antigen alone. To elucidate the mechanisms underlying the adjuvant effect of SO-GS-R, we measured cytokines in serum and muscle tissue after intramuscular injection of SO-GS-R. The results showed that injection of SO-GS-R significantly increased the levels of IL-1β, IL-5, IL-6, G-CSF, KC, MCP-1, MIP-1α, and MIP-1β in both serum and muscle. These results suggested that SO-GS-R recruits neutrophils, eosinophils, T cells and macrophages, causing immune cell recruitment at the injection site, driving antigen-presenting cells to actively participate in the onset of immunity, and amplifying the immune responses. Considering its adjuvant activity and plant-derived properties, SO-GS-R should be further studied for its adjuvant effect on vaccines used in food animals.

Chlamydia trachomatis and chlamydia-like bacteria: new enemies of human pregnancies

PURPOSE OF REVIEW

This review provides an update on the roles of Chlamydia trachomatis and the related Waddlia chondrophila and Parachlamydia acanthamoebae in miscarriage, stillbirths and preterm labour in humans. A broad audience, including microbiologist, infectiologists, obstetricians and gynaecologists, should be aware of the potential threat of these Chlamydiales for human reproduction.

RECENT FINDINGS

Despite increasing laboratory techniques and possibilities to perform diagnostic tests, the cause of miscarriage is only identified in 50% of the cases. Intracellular bacteria, such as C. trachomatis and Chlamydia-related bacteria, are difficult to detect in routine clinical samples and could represent possible agents of miscarriages. C. trachomatis is considered the world largest sexual transmitted bacterial agent and is associated with adverse pregnancy outcome in human. In the last decade Chlamydia-like organisms, such as W. chondrophila and P. acanthamoebae, have also been associated with adverse pregnancy outcomes in human and/or animals.

SUMMARY

We review here the current evidences for a pathogenic role in humans, the diagnostic approaches and possible treatment options of C. trachomatis, W. chondrophila and P. acanthamoebae.