Gastrointestinal Coinfection Promotes Chlamydial Pathogenicity in the Genital Tract

Development and Validation of Chlamydia muridarum Mouse Models for Studying Genital Tract Infection Pathogenesis

Animal infection models play significant roles in the study of bacterial pathogenic mechanisms and host-pathogen interactions, as well as in evaluating drug and vaccine efficacies. Chlamydia trachomatis is responsible for infections in various mucosal tissues, including the eyes and urogenital, respiratory, and gastrointestinal tracts. Chronic infections can result in severe consequences such as trachoma-induced blindness, ectopic pregnancy, and infertility. While intravaginal inoculation of C. muridarum mimics the natural route of sexual transmission between individuals, transcervical inoculation allows the organisms to directly infect endometrial epithelial cells without interference from host responses triggered by chlamydial contact or infection of vaginal and cervical cells. Therefore, in this study, we used mouse models to visualize pathologies in both the endometrium and oviduct following C. muridarum inoculation. Key features • This protocol develops the mouse-adapted Chlamydia muridarum model, ideal for visualizing pathologies in both the endometrium and oviduct genital tract. • Requires female mice and utilizes specific techniques for intravaginal and transcervical inoculation with chlamydial elementary body (EB) and a form specialized for intracellular replication. • The protocol necessitates specialized equipment, including a laminar flow hood, a micropipette, and a non-surgical embryo transfer device (NSET). Graphical overview.

Highly viable gastrointestinal Chlamydia trachomatis in women abstaining from receptive anal intercourse

Chlamydia trachomatis (CT) may employ persistence to evade antimicrobial clearance, possibly residing in the gastrointestinal tract. This study assessed the reliability of droplet digital PCR (ddPCR) in CT detection, its functionality in viability assessment, and predictions on CT transmission dynamics by combining viability PCR (vPCR) and clinical data from 52 infected women. The ddPCR showed 94% positive and 100% negative agreement with Abbott Alinity STI-M for endocervical samples, and 92% positive and 87% negative agreement in rectal samples. Viability was higher in endocervical samples (89.1%) than in rectal samples (69.4%). Samples from participants not engaging in anal intercourse, and with non-concordant multi-locus sequence typing between rectum and endocervix, had on average the highest viability in rectum, indicating a persistent population residing in the gastrointestinal tract. This study demonstrates the effectiveness of ddPCR in detecting CT, especially in samples with high inhibition or low bacterial load, suggesting its superiority over quantitative real-time PCR. These findings support that rectal CT infection can occur independently of anal intercourse, possibly through vaginorectal contamination or oral routes. High rectal CT viability, independent of endocervical infection, indicates potential gastrointestinal establishment. Understanding CT dynamics in various infection sites can provide insights into the epidemiology and pathogenesis of CT.

Efficacy of a Novel Affitoxin Targeting Major Outer Membrane Protein Against Chlamydia trachomatis In Vitro and In Vivo

Targeted therapy is an attractive approach for treating infectious diseases. Affibody molecules have similar capability to antibodies that facilitate molecular recognition in both diagnostic and therapeutic applications. Targeting major outer membrane protein (MOMP) for treating infection of Chlamydia trachomatis, one of the most common sexually transmitted pathogens, is a promising therapeutic approach. Previously, we have reported a MOMP-specific affibody (ZMOMP:461) from phage display library. Here, we first fused it with modified Pseudomonas exotoxin (PE38KDEL) and a cell-penetrating peptide (CPP) to develop an affitoxin, Z461X-CPP. We then verified the addition of both toxin and CPPs that did not affect the affinitive capability of ZMOMP:461 to MOMP. Upon uptake by C trachomatis-infected cells, Z461X-CPP induced cell apoptosis in vitro. In an animal model, Z461X significantly shortened the duration of C trachomatis infection and prevented pathological damage in the mouse reproductive system. These findings provide compelling evidence that the MOMP-specific affitoxin has great potential for targeting therapy of C trachomatis infection.

Diverse animal models for Chlamydia infections: unraveling pathogenesis through the genital and gastrointestinal tracts

Chlamydia trachomatis is responsible for infections in various mucosal tissues, including the eyes, urogenital, respiratory, and gastrointestinal tracts. Chronic infections can result in severe consequences such as blindness, ectopic pregnancy, and infertility. The underlying mechanisms leading to these diseases involve sustained inflammatory responses, yet thorough comprehension of the underlying mechanisms remains elusive. Chlamydial biologists employ in multiple methods, integrating biochemistry, cell biology, and genetic tools to identify bacterial factors crucial for host cell interactions. While numerous animal models exist to study chlamydial pathogenesis and assess vaccine efficacy, selecting appropriate models for biologically and clinically relevant insights remains a challenge. Genital infection models in animals have been pivotal in unraveling host-microbe dynamics, identifying potential chlamydial virulence factors influencing genital pathogenicity. However, the transferability of this knowledge to human pathogenic mechanisms remains uncertain. Many putative virulence factors lack assessment in optimal animal tissue microenvironments, despite the diverse chlamydial infection models available. Given the propensity of genital Chlamydia to spread to the gastrointestinal tract, investigations into the pathogenicity and immunological impact of gut Chlamydia become imperative. Notably, the gut emerges as a promising site for both chlamydial infection vaccination and pathogenesis. This review elucidates the pathogenesis of Chlamydia infections and delineates unique features of prevalent animal model systems. The primary focus of this review is to consolidate and summarize current animal models utilized in Chlamydia researches, presenting findings, discussions on their contributions, and suggesting potential directions for further studies.

Regulation of chlamydial spreading from the small intestine to the large intestine by IL-22-producing CD4+ T cells

Following an oral inoculation, Chlamydia muridarum descends to the mouse large intestine for long-lasting colonization. However, a mutant C. muridarum that lacks the plasmid-encoded protein pGP3 due to an engineered premature stop codon (designated as CMpGP3S) failed to do so even following an intrajejunal inoculation. This was because a CD4+ T cell-dependent immunity prevented the spread of CMpGP3S from the small intestine to the large intestine. In the current study, we found that mice deficient in IL-22 (IL-22-/-) allowed CMpGP3S to spread from the small intestine to the large intestine on day 3 after intrajejunal inoculation, indicating a critical role of IL-22 in regulating the chlamydial spread. The responsible IL-22 is produced by CD4+ T cells since IL-22-/- mice were rescued to block the CMpGP3S spread by donor CD4+ T cells from C57BL/6J mice. Consistently, CD4+ T cells lacking IL-22 failed to block the spread of CMpGP3S in Rag2-/- mice, while IL-22-competent CD4+ T cells did block. Furthermore, mice deficient in cathelicidin-related antimicrobial peptide (CRAMP) permitted the CMpGP3S spread, but donor CD4+ T cells from CRAMP-/- mice were still sufficient for preventing the CMpGP3S spread in Rag2-/- mice, indicating a critical role of CRAMP in regulating chlamydial spreading, and the responsible CRAMP is not produced by CD4+ T cells. Thus, the IL-22-producing CD4+ T cell-dependent regulation of chlamydial spreading correlated with CRAMP produced by non-CD4+ T cells. These findings provide a platform for further characterizing the subset(s) of CD4+ T cells responsible for regulating bacterial spreading in the intestine.

Neisseria gonorrhoeae Coinfection during Chlamydia muridarum Genital Latency Does Not Modulate Murine Vaginal Bacterial Shedding

Chlamydia trachomatis and Neisseria gonorrhoeae are the most frequently reported agents of bacterial sexually transmitted disease worldwide. Nonetheless, C. trachomatis/N. gonorrhoeae coinfection remains understudied. C. trachomatis/N. gonorrhoeae coinfections are more common than expected by chance, suggesting C. trachomatis/N. gonorrhoeae interaction, and N. gonorrhoeae infection may reactivate genital chlamydial shedding in women with latent (quiescent) chlamydial infection. We hypothesized that N. gonorrhoeae would reactivate latent genital Chlamydia muridarum infection in mice. Two groups of C. muridarum-infected mice were allowed to transition into genital latency. One group was then vaginally inoculated with N. gonorrhoeae; a third group received N. gonorrhoeae alone. C. muridarum and N. gonorrhoeae vaginal shedding was measured over time in the coinfected and singly infected groups. Viable C. muridarum was absent from vaginal swabs but detected in rectal swabs, confirming C. muridarum genital latency and consistent with the intestinal tract as a C. muridarum reservoir. C. muridarum inclusions were observed in large intestinal, but not genital, tissues during latency. Oviduct dilation was associated with C. muridarum infection, as expected. Contradicting our hypothesis, N. gonorrhoeae coinfection did not reactivate latent C. muridarum vaginal shedding. In addition, latent C. muridarum infection did not modulate recovery of vaginal viable N. gonorrhoeae. Evidence for N. gonorrhoeae-dependent increased C. muridarum infectivity has thus not been demonstrated in murine coinfection, and the ability of C. muridarum coinfection to potentiate N. gonorrhoeae infectivity may depend on actively replicating vaginal C. muridarum. The proportion of mice with increased vaginal neutrophils (PMNs) was higher in N. gonorrhoeae-infected than in C. muridarum-infected mice, as expected, while that of C. muridarum/N. gonorrhoeae-coinfected mice was intermediate to the singly infected groups, suggesting latent C. muridarum murine infection may limit PMN response to subsequent N. gonorrhoeae infection. IMPORTANCE Our work builds upon the limited understanding of C. muridarum/N. gonorrhoeae coinfection. Previously, N. gonorrhoeae infection of mice with acute (actively replicating) vaginal C. muridarum infection was shown to increase recovery of viable vaginal N. gonorrhoeae and vaginal PMNs, with no effect on C. muridarum vaginal shedding (R. A. Vonck et al., Infect Immun 79:1566-1577, 2011). It has also been shown that chlamydial infection of human and murine PMNs prevents normal PMN responses, including the response to N. gonorrhoeae (K. Rajeeve et al., Nat Microbiol 3:824-835, 2018). Our findings show no effect of latent genital C. muridarum infection on the recovery of viable N. gonorrhoeae, in contrast to the previously reported effect of acute C. muridarum infection, and suggesting that acute versus latent C. muridarum infection may have distinct effects on PMN function in mice. Together, these studies to date provide evidence that Chlamydia/N. gonorrhoeae synergistic interactions may depend on the presence of replicating Chlamydia in the genital tract, while chlamydial effects on vaginal PMNs may extend beyond acute infection.

Regulation of chlamydial colonization by IFNγ delivered via distinct cells

The mouse-adapted pathogen Chlamydia muridarum (CM) induces pathology in the mouse genital tract but fails to do so in the gastrointestinal tract. CM is cleared from both the genital tract and small intestine by IFNγ delivered by antigen-specific CD4+ T cells but persists for a long period in the large intestine. The long-lasting colonization of CM in the large intestine is regulated by IFNγ delivered by group 3 innate lymphoid cells (ILC3s). Interestingly, the ILC3-delivered IFNγ can inhibit the human pathogen Chlamydia trachomatis (CT) in the mouse endometrium. Thus, IFNγ produced/delivered by different cells may selectively restrict chlamydial colonization in different tissues. Revealing the underlying mechanisms of chlamydial interactions with IFNγ produced by different cells may yield new insights into both chlamydial pathogenicity and mucosal immunity.

Lactobacillus Modulates Chlamydia Infectivity and Genital Tract Pathology in vitro and in vivo

Since we previously reported that women infected with chlamydia had a significant overall reduction in Lactobacillus in the vagina microbiota as compared to those uninfected individuals; the interactions between the altered Lactobacillus and Chlamydia trachomatis, on the other hand, need to be elucidated. Here, we employed both in vitro and in vivo models to evaluate the effects of this changed Lactobacillus on Chlamydia infection. We found that L. iners, L. crispatus, L. jensenii, L. salivarius, L. gasseri, L. mucosae, and L. reuteri all significantly reduced C. trachomatis infection in a dose- and time-dependent manner. The strongest anti-Chlamydia effects were found in L. crispatus (90 percent reduction), whereas the poorest was found in L. iners (50 percent reduction). D (–) lactic acid was the key component in Lactobacillus cell-free supernatants (CFS) to inactivate Chlamydia EBs, showing a positive correlation with the anti-Chlamydia activity. The effects of D (–) lactic acid were substantially attenuated by neutralizing the pH value to 7.0. In vivo, mice intravaginally inoculated with Lactobacillus mixtures (L. crispatus, L. reuteri, and L. iners at a ratio of 1:1:1), but not single Lactobacillus, after genital Chlamydia infection, significantly attenuated the levels of Chlamydia live organism shedding in both the lower genital tract and the intestinal tract, reduced cytokines production (TNF-α, IFN-γ, and IL-1β) in the vagina, and lessened upper genital tract inflammation and pathogenicity. Taken together, these data demonstrate that Lactobacillus inhibits Chlamydia infectivity both in vivo and in vitro, providing useful information for the development of Lactobacillus as adjunctive treatment in Chlamydia infection.

Chlamydia Deficient in Plasmid-Encoded Glycoprotein 3 (pGP3) as an Attenuated Live Oral Vaccine

Despite the extensive efforts, there is still a lack of a licensed vaccine against Chlamydia trachomatis in humans. The mouse genital tract infection with Chlamydia muridarum has been used to both investigate chlamydial pathogenic mechanisms and evaluate vaccine candidates due to the C. muridarum's ability to induce mouse hydrosalpinx. C. muridarum mutants lacking the entire plasmid or deficient in only the plasmid-encoded pGP3 are highly attenuated in inducing hydrosalpinx. We now report that intravaginal immunization with these mutants as live attenuated vaccines protected mice from hydrosalpinx induced by wild type C. muridarum. However, these mutants still productively infected the mouse genital tract. Further, the mutant-infected mice were only partially protected against the subsequent infection with wild type C. muridarum. Thus, these mutants as vaccines are neither safe nor effective when they are delivered via the genital tract. Interestingly, these mutants were highly deficient in colonizing the gastrointestinal tract. Particularly, the pGP3-deficient mutant failed to shed live organisms from mice following an oral inoculation, suggesting that the pGP3-deficient mutant may be developed into a safe oral vaccine. Indeed, oral inoculation with the pGP3-deficient mutant induced robust transmucosal immunity against both the infection and pathogenicity of wild type C. muridarum in the genital tract. Thus, we have demonstrated that the plasmid-encoded virulence factor pGP3 may be targeted for developing an attenuated live oral vaccine.

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.

Lactobacillus rhamnosus GG attenuates the pathology of Chlamydial muridarium in the upper genital tract in mice

OBJECTIVES

Chlamydia trachomatis is a pathogen which can cause hydrosalpinx and tubal fibrosis when infecting the urogenital tract. However, the mechanism is still not clear. There is growing evidence that the gut microbiota is associated with the pathogenesis of both intestinal and extra-intestinal disorders, such as cardiovascular disease, hepatocirrhosis, allergy, respiratory tract infection, polycystic ovary syndrome, endometriosis, and bacterial vaginitis. Lactobacillus rhamnosus GG (LGG) is one of the most extensively studied and widely used probiotic bacteria, the benefits of LGG including the treatment in gastrointestinal disorders and immunomodulation are well demonstrated, and it can also alleviate hypersensitivity reaction and diarrhoea, inhibit a variety of respiratory and urogenital diseases. Chlamydia muridarium (Cm) infection is a good model for the study on human Chlamydia pathogenicity in genitourinary tract. The mice infected with Cm were used as animal models to preliminarily explore the mechanism for the effect of LGG on upper reproductive tract infection in the mice, and to provide experimental basis for the pathogenesis of Chlamydia trachomatis genitourinary tract infection and the new idea for the treatment of Chlamydia trachomatis infection.

METHODS

Five to six weeks-old C57BL/6J mice were divided into 2 groups: An experimental group and a control group. The experimental group were administrated with 5×108 colony forming units (CFU) LGG for 19 consecutive days, while the control group were feed PBS. The mice in the 2 group were subcutaneously injected with 2.5 mg progesterone on Day 9 and infected with 1×105 inclusion body forming unit of Cm via the vaginal tract on Day 14. Vaginal and rectal swabs were taken every 7 days to infect HeLa cells for 24 hours, then the indirect immunofluorescence assay was used and the number of inclusion bodies of Chlamydia were calculated. Mice were euthanized on Day 14 and Day 63 after Cm inoculation, the vaginal tracts were dissected, and the tissue homogenates were prepared to culture the pathogens for 24 hours. The Cm bearing capacity in the bilateral uterine horn, tubal ovary, and cervical vaginal tissues in the 2 groups were calculated. The spleen cells were harvested to assay the intracellular IFN-γ, IL-5, and IL-17 by flow cytometry. On Day 63 after the Chlamydia infection, the pathology injury in the bilateral uterine horn and oviduct was observed, and the pathological sections and HE staining in the various part of genital tract were performed. The inflammatory cell infiltration and lumen dilatation was assessed. The specific IgM and IgG in sera were detected by indirect ELISA on Day 14 and 63 after infection.

RESULTS

There was no effect of LGG on the clearing of Cm from the urogenital tract, the Chlamydia ascending to fallopian tube or the uterine horn, and the organism dissemination and colonization to the gastrointestinal tract (all P>0.05). On Day 14 after Cm infection via the vagina, the IL-17 expression level in the experimental group was significant decreased than that in the control group (t=2.486, P<0.05), but there was no significant difference between the 2 groups in the CD4+ T rate in spleen and IgM and IgG levels in serum after Cm intravaginal infection (all P>0.05). On Day 63 after Cm infection, there was no difference in the severity of inflammation in the uterine horns and fallopian tubes between the 2 groups (P>0.05), but the dilation of the fallopian tubes and hydrosalpinx was attenuated in the experimental group compared with the control group (P<0.05).

CONCLUSIONS

Oral administration of LGG has no effect on inhibiting Cm ascending to upper genital tract and preventing the dissemination and colonization of Cm to the gastrointestinal tract, which also cannot affect the secretion of specific IgM and IgG in sera. Oral administration of LGG can suppress the production of IL-17 in the spleen cells and attenuate hydrosalpinx development when following Cm intravaginal infection in mice.

Characterization of pathogenic CD8+ T cells in Chlamydia-infected OT1 mice

Chlamydia trachomatis is a leading infectious cause of infertility in women due to its induction of lasting pathology such as hydrosalpinx. Chlamydia muridarum induces mouse hydrosalpinx because C. muridarum can both invade tubal epithelia directly (as a 1^st hit) and induce lymphocytes to promote hydrosalpinx indirectly (as a 2^nd hit). In the current study, a critical role of CD8⁺ T cells in chlamydial induction of hydrosalpinx was validated in both wild type C57BL/6J and OT1 transgenic mice. OT1 mice failed to develop hydrosalpinx partially due to the failure of their lymphocytes to recognize chlamydial antigens. CD8⁺ T cells from naïve C57BL/6J rescued the recipient OT1 mice to develop hydrosalpinx when naïve CD8⁺ T cells were transferred at the time of infection with Chlamydia. However, when the transfer was delayed for 2 weeks or longer after the chlamydial infection, naïve CD8⁺ T cells no longer promoted hydrosalpinx. Nevertheless, Chlamydia-immunized CD8⁺ T cells still promoted significant hydrosalpinx in the recipient OT1 mice even when the transfer was delayed for 3 weeks. Thus, CD8⁺ T cells must be primed within 2 weeks after chlamydial infection to be pathogenic but once primed, they can promote hydrosalpinx for >3 weeks. However, Chlamydia-primed CD4⁺ T cells failed to promote chlamydial induction of pathology in OT1 mice. This study has optimized an OT1 mouse-based model for revealing the pathogenic mechanisms of Chlamydia-specific CD8⁺ T cells.

Chlamydia spreads to the large intestine lumen via multiple pathways

Chlamydia in the genital tract is known to spread via the blood circulation system to the large intestinal lumen to achieve long-lasting colonization. However, the precise pathways for genital Chlamydia to access to the large intestinal lumen remain unclear. The spleen was recently reported to be critical for the chlamydial spreading. In the current study, it was found that following intravaginal inoculation with Chlamydia, mice with or without splenectomy both produced infectious Chlamydia in the rectal swabs, indicating that spleen is not essential for genital Chlamydia to spread to the gastrointestinal tract. This conclusion was validated by the observation that intravenously inoculated Chlamydia was also detected in the rectal swabs of mice regardless of splenectomy. Careful comparison of the tissue distribution of live chlamydial organisms following intravenous inoculation revealed redundant pathways for Chlamydia to reach the large intestine lumen. The intravenously inoculated Chlamydia was predominantly recruited to the spleen within 12h and then detected in the stomach lumen by 24h, the intestinal lumen by 48h and rectal swabs by 72h. These observations suggest a potential spleen-to-stomach pathway for hematogenous Chlamydia to reach the large intestine lumen. This conclusion was supported by the observation made in mice under coprophagy-free condition. However, in the absence of spleen, hematogenous Chlamydia was predominantly recruited to the liver and then simultaneously detected in the intestinal tissue and lumen, suggesting a potential liver-to-intestine pathway for Chlamydia to reach the large intestine lumen. Thus, genital/hematogenous Chlamydia may reach the large intestinal lumen via multiple redundant pathways.

Gastrointestinal Chlamydia-induced CD8+ T cells promote chlamydial pathogenicity in the female upper genital tract

Chlamydia is known to both ascend to the upper genital tract and spread to the gastrointestinal tract following intravaginal inoculation. The gastrointestinal Chlamydia was recently reported to promote chlamydial pathogenicity in the genital tract since mice intravaginally inoculated with an attenuated Chlamydia, which alone failed to develop pathology in the genital tract, were restored to develop hydrosalpinx by intragastric co-inoculation with wild type Chlamydia. Gastrointestinal Chlamydia promoted hydrosalpinx via an indirect mechanism since Chlamydia in the gut did not directly spread to the genital tract lumen. In the current study, we further investigated the role of CD8⁺ T cells in the promotion of hydrosalpinx by gastrointestinal Chlamydia. First, we confirmed that intragastric co-inoculation with wild type Chlamydia promoted hydrosalpinx in mice that were inoculated with an attenuated Chlamydia in the genital tract one week earlier. Second, the promotion of hydrosalpinx by intragastrically co-inoculated Chlamydia was blocked by depleting CD8⁺ T cells. Third, adoptive transfer of the gastrointestinal Chlamydia-induced CD8⁺ T cells was sufficient for promoting hydrosalpinx in mice that were intravaginally inoculated with an attenuated Chlamydia. These observations have demonstrated that CD8⁺ T cells induced by gastrointestinal Chlamydia are both necessary and sufficient for promoting hydrosalpinx in the genital tract. The study has laid a foundation for further revealing the mechanisms by which Chlamydia-induced T lymphocyte responses (as a 2^nd hit) promote hydrosalpinx in mice with genital Chlamydia-triggered tubal injury (as a 1^st hit), a continuing effort in testing the two-hit hypothesis as a chlamydial pathogenic mechanism.

Chlamydia overcomes multiple gastrointestinal barriers to achieve long-lasting colonization

Chlamydia trachomatis (CT) is frequently detected in the human gastrointestinal (GI) tract despite its leading role in sexually transmitted bacterial infections in the genital tract. Chlamydia muridarum (CM), a model pathogen for investigating CT pathogenesis in the genital tract, can also colonize the mouse GI tract for long periods. Genital-tract mutants of CM no longer colonize the GI tract. The mutants lacking plasmid functions are more defective in colonizing the upper GI tract while certain chromosomal gene-deficient mutants are more defective in the lower GI tract, suggesting that Chlamydia may use the plasmid for promoting its spread to the large intestine while using the chromosome-encoded factors for maintaining its colonization in the large intestine. The plasmid-encoded Pgp3 is critical for Chlamydia to resist the acid barrier in the stomach and to overcome a CD4⁺ T cell barrier in the small intestine. On reaching the large intestine, Pgp3 is no longer required. Instead, the chromosome-encoded open reading frames TC0237/TC0668 become essential for Chlamydia to evade the group 3-like innate lymphoid cell-secreted interferon (IFN)γ in the large intestine. These findings are important for exploring the medical significance of chlamydial colonization in the gut and for understanding the mechanisms of chlamydial pathogenicity in the genital tract.

Immunopathogenesis of genital Chlamydia infection: insights from mouse models

Chlamydiae are pathogenic intracellular bacteria that cause a wide variety of diseases throughout the globe, affecting the eye, lung, coronary arteries and female genital tract. Rather than by direct cellular toxicity, Chlamydia infection generally causes pathology by inducing fibrosis and scarring that is largely mediated by host inflammation. While a robust immune response is required for clearance of the infection, certain elements of that immune response may also damage infected tissue, leading to, in the case of female genital infection, disease sequelae such as pelvic inflammatory disease, infertility and ectopic pregnancy. It has become increasingly clear that the components of the immune system that destroy bacteria and those that cause pathology only partially overlap. In the ongoing quest for a vaccine that prevents Chlamydia-induced disease, it is important to target mechanisms that can achieve protective immunity while preventing mechanisms that damage tissue. This review focuses on mouse models of genital Chlamydia infection and synthesizes recent studies to generate a comprehensive model for immunity in the murine female genital tract, clarifying the respective contributions of various branches of innate and adaptive immunity to both host protection and pathogenic genital scarring.

Regulation of Chlamydia spreading from the small intestine to the large intestine via an immunological barrier

The obligate intracellular bacterium Chlamydia is a genital tract pathogen that can also colonize the gastrointestinal tract for long periods. The long-lasting colonization is dependent on chlamydial spreading from the small intestine to the large intestine. We previously reported that a mutant Chlamydia was able to activate an intestinal barrier for blocking its own spreading to the large intestine. In the current study, we used the mutant Chlamydia colonization model to confirm the intestinal barrier function and further to determine the immunological basis of the barrier with gene-deficient mice. Recombination activating gene 1^-/- mice failed to block the mutant Chlamydia spreading, while mice deficient in toll-like receptors, myeloid differentiation primary response 88 or stimulator of interferon genes still blocked the spreading, suggesting that the intestinal barrier function is dependent on lymphocytes that express antigen receptors. Mice deficient in CD4, but not CD8 nor μ chain failed to prevent the chlamydial spreading, indicating a protective role of CD4⁺ cells in the intestinal barrier. Consistently, adoptive transfer of CD4⁺ T cells reconstituted the intestinal barrier in CD4^-/- mice. More importantly, CD4⁺ but not CD8⁺ T cells nor B cells restored the intestinal barrier function in recombination activating gene 1^-/- mice. Thus, CD4⁺ T cells are necessary and sufficient for maintaining the intestinal barrier function, indicating that the spread of an intracellular bacterium from the small intestine to the large intestine is regulated by an immunological barrier. This study has also laid a foundation for further illuminating the mechanisms by which a CD4⁺ T cell-dependent intestinal barrier regulates bacterial spreading in the gut.

Effects of Immunomodulatory Drug Fingolimod (FTY720) on Chlamydia Dissemination and Pathogenesis

Fingolimod (FTY720), an FDA-approved immunomodulatory drug for treating multiple sclerosis, is an agonist of sphingosine-1-phosphate receptor (S1PR), which has been used as a research tool for inhibiting immune cell trafficking. FTY720 was recently reported to inhibit Chlamydia dissemination. Since genital Chlamydia spreading to the gastrointestinal tract correlated with its pathogenicity in the upper genital tract, we evaluated the effect of FTY720 on chlamydial pathogenicity in the current study. Following an intravaginal inoculation, live chlamydial organisms were detected in mouse rectal swabs. FTY720 treatment significantly delayed live organism shedding in the rectal swabs. However, FTY720 failed to block chlamydial spreading to the gastrointestinal tract. The live chlamydial organisms recovered from rectal swabs reached similar levels between mice with or without FTY720 treatment by day 42 in C57BL/6J and day 28 in CBA/J mice, respectively. Thus, genital Chlamydia is able to launch a 2nd wave of spreading via an FTY720-resistant pathway after the 1st wave of spreading is inhibited by FTY720. As a result, all mice developed significant hydrosalpinx. The FTY720-resistant spreading led to stable colonization of chlamydial organisms in the colon. Consistently, FTY720 did not alter the colonization of intracolonically inoculated Chlamydia Thus, we have demonstrated that, following a delay in chlamydial spreading caused by FTY720, genital Chlamydia is able to both spread to the gastrointestinal tract via an FTY720-resistant pathway and maintain its pathogenicity in the upper genital tract. Further characterization of the FTY720-resistant pathway(s) explored by Chlamydia for spreading to the gastrointestinal tract may promote our understanding of Chlamydia pathogenic mechanisms.