Chlamydia muridarum-Specific CD4 T-Cell Clones Recognize Infected Reproductive Tract Epithelial Cells in an Interferon-Dependent Fashion

During natural infections Chlamydia trachomatis urogenital serovars replicate predominantly in the epithelial cells lining the reproductive tract. This tissue tropism poses a unique challenge to host cellar immunity and future vaccine development. In the experimental mouse model, CD4 T cells are necessary and sufficient to clear Chlamydia muridarum genital tract infections. This implies that resolution of genital tract infection depends on CD4 T-cell interactions with infected epithelial cells. However, no laboratory has shown that Chlamydia-specific CD4 T cells can recognize Chlamydia antigens presented by major histocompatibility complex class II (MHC-I) molecules on epithelial cells. In this report we show that MHC-II-restricted Chlamydia-specific CD4 T-cell clones recognize infected upper reproductive tract epithelial cells as early as 12 h postinfection. The timing of recognition and degree of T-cell activation are dependent on the interferon (IFN) milieu. Beta IFN (IFN-β) and IFN-γ have different effects on T-cell activation, with IFN-β blunting IFN-γ-induced upregulation of epithelial cell surface MHC-II and T-cell activation. Individual CD4 T-cell clones differed in their degrees of dependence on IFN-γ-regulated MHC-II for controlling Chlamydia replication in epithelial cells in vitro. We discuss our data as they relate to published studies with IFN knockout mice, proposing a straightforward interpretation of the existing literature based on CD4 T-cell interactions with the infected reproductive tract epithelium.Chlamydia trachomatis is the most common bacterial sexually transmitted infection in the developed world, with 2 to 3 million actively infected individuals in the United States (3) and similar numbers in Europe (17). In women C. trachomatis infections can ascend into the upper reproductive tract, causing pelvic inflammatory disease and scarring with resulting infertility and ectopic pregnancies.Histopathology studies show that C. trachomatis replicates predominantly in the reproductive tract epithelium during natural human infections (16, 36) and experimental murine C. muridarum infections (21). Inclusions are not seen in other cell types even though Chlamydia can undergo limited replication in macrophages and dendritic cells (33). It is unlikely that replication in non-epithelial cell lineages makes a major contribution to genital tract shedding. The mouse model for Chlamydia genital tract infections supports a critical role for CD4 T cells in protective immunity, as mice deficient in major histocompatibility complex class II (MHC-II) cannot control C. muridarum genital tract infections (22), and CD4 T-cell depletion is detrimental to resolution of primary genital tract infections (23). Because C. muridarum replicates in epithelial cells lining the reproductive tract, the most straightforward mechanism for clearing the genital tract would involve Chlamydia-specific CD4 T-cell interactions with infected epithelial cells. However in the absence of any data supporting this specific interaction, other indirect mechanisms based on CD4 T-cell production of gamma interferon (IFN-γ) and provision of help to B cells and CD8 T cells have been proposed as the mechanism for clearance (29).C. muridarum-specific CD4 T-cell lines protective in adoptive-transfer studies were shown to control C. muridarum replication in polarized epithelial monolayers (14). The mechanism of control was dependent on IFN-γ and physical interaction of T cells with the infected epithelial cells via LFA-1. In the presence of IFN-γ, T-cell engagement of epithelial cells via LFA-1 was shown to augment epithelial nitric oxide production above that induced by IFN-γ alone, and nitric oxide was shown to be the effector molecule responsible for controlling Chlamydia replication (13). This anti-Chlamydia effector mechanism did not require that the CD4 T-cell clone recognize the infected epithelial monolayer in an antigen-specific fashion, as the same preactivated CD4 T-cell clone controlled Chlamydia psittaci replication in polarized epithelial monolayers even though it does not recognize a C. psittaci antigen.Epithelial cells are semiprofessional antigen-presenting cells (APCs) and, in their unperturbed state, likely play a role in immunotolerance at mucosal surfaces (19). However in inflammatory environments, such as those resulting from transplant rejection and graft-versus-host disease, epithelial cells change their immunophenotype by upregulation of MHC-II (5, 25). In trachoma, an eye infection caused by Chlamydia trachomatis serovars A to C, conjunctival epithelial cells from human clinical specimens showed upregulated cell surface MHC-II and were presumably competent to present antigens to CD4 T cells (11, 12). In vitro studies have shown that rat and murine uterine epithelial cells process and present exogenous ovalbumin to OVA-specific CD4 T cells (28, 37). However in vitro processing and presentation of concentrated extracellular ovalbumin to CD4 T cells by uterine epithelial cells do not directly address whether Chlamydia antigens sequestered in membrane-bound inclusions get processed and presented to Chlamydia-specific CD4 T cells in vivo. The mechanics of CD4 T-cell contributions to resolution of genital tract infections remain unclear.For this study we derived an epithelial cell line from the upper reproductive tract of a female C57BL/6 mouse and a panel of 10 Chlamydia-specific CD4 T-cell clones from immune C57BL/6 mice that previously self-cleared C. muridarum genital tract infections. These reagents gave us the opportunity to directly investigate (i) whether Chlamydia-specific CD4 T cells can recognize C. muridarum-infected reproductive tract epithelial cells, (ii) when during the time course of infection recognition occurs, and (iii) the role of IFNs in modulating epithelial interactions with CD4 T cells. We present the results of those investigations here.(These data were presented in part at the 2009 Chlamydia Basic Research Conference.)     

Chlamydial Infection in Inducible Nitric Oxide Synthase Knockout Mice

Type 1 CD4⁺-T-cell-mediated immunity is crucial for the resolution of chlamydial infection of the murine female genital tract. Previous studies demonstrating a correlation between CD4⁺-T-cell-mediated inhibition of chlamydial growth and gamma interferon (IFN-γ)-mediated induction of nitric oxide synthase suggested a potential role for the nitric oxide (NO) effector pathway in the clearance of Chlamydia from genital epithelial cells by the immune system. To clarify the role of this pathway, the growth levels of Chlamydia trachomatis organisms in normal (iNOS^+/+) mice and in genetically engineered mice lacking the inducible nitric oxide synthase (iNOS) gene (iNOS^−/− mice) were compared. There was no significant difference in the course of genital chlamydial infections in iNOS^+/+ and iNOS^−/− mice as determined by recovery of Chlamydia organisms shed from genital epithelial cells. Dissemination of Chlamydia to the spleen and lungs occurred to a greater extent in iNOS^−/− than in iNOS^+/+ mice, which correlated with a marginal increase in the susceptibility of macrophages from iNOS^−/− mice to chlamydial infection in vitro. However, infections were rapidly cleared from all affected tissues, with no clinical signs of disease. The finding of minimal dissemination in iNOS^−/− mice suggested that activation of the iNOS effector pathway was not the primary target of IFN-γ during CD4⁺-T-cell-mediated control of chlamydial growth in macrophages because previous reports demonstrated extensive and often fatal dissemination of Chlamydia in mice lacking IFN-γ. In summary, these results indicate that the iNOS effector pathway is not required for elimination of Chlamydia from epithelial cells lining the female genital tract of mice although it may contribute to the control of dissemination of C. trachomatis by infected macrophages.     

Gamma Interferon Production by Cytotoxic T Lymphocytes Is Required for Resolution of Chlamydia trachomatis Infection

In this study, we used mice in which the gene for gamma interferon (IFN-γ) has been disrupted (IFN-γ^−/− mice) to study the role of this cytokine in the resolution of Chlamydia trachomatis infection. We show that IFN-γ^−/− mice are impaired in the ability to clear infection with C. trachomatis compared to IFN-γ^+/+ control mice. Activated CD8⁺ cytotoxic T lymphocytes (CTL) secrete IFN-γ in response to intracellular infection, and we have shown previously that a Chlamydia-specific CTL line can reduce C. trachomatis infection when adoptively transferred into infected mice. In the present study, we found that when these IFN-γ^+/+ CTL lines are transferred into Chlamydia-infected IFN-γ^−/− mice, the transferred CTL cannot overcome the immune defect seen in the IFN-γ^−/− mice. We also show that Chlamydia-specific CTL can be cultured from IFN-γ-deficient mice infected with C. trachomatis; however, the adoptive transfer of IFN-γ^−/− CTL into infected IFN-γ^+/+ mice does not reduce the level of infection. These results suggest that IFN-γ production by CTL is not sufficient to overcome the defect that IFN-γ^−/− mice have in the resolution of Chlamydia infection, yet IFN-γ production by CTL is required for the protective effect seen upon adoptive transfer of CTL into IFN-γ^+/+ mice.     

Vaccination with MIP or Pgp3 induces cross-serovar protection against chlamydial genital tract infection in mice

Previously we reported that recombinant Chlamydia muridarum macrophage infectivity potentiator (MIP) provided partial protection against C. muridarum genital tract infection in mice. On the other hand, Chlamydia trachomatis plasmid encoded Pgp3could induce the protection against C. muridarum air way infection. This study aimed to evaluate the immunogenicity of MIP and Pgp3 from C. trachomatis serovar D and further investigate whether MIP and Pgp3 provide cross-serovar protection against C. muridarum genital tract infection in mice. Our results showed that vaccination by any regimen, including MIP alone, Pgp3 alone or MIP plus Pgp3, induced specific serum antibody production and Th1-dominant cellular responses in mice. Live chlamydial shedding from the vaginal and inflammatory pathologies in the oviduct markedly reduced. However, MIP?+?Pgp3 vaccination did not provide better protection than the single immunization. In conclusion, this study demonstrated that both MIP and Pgp3 can induce cross-serovar protective against chlamydial genital tract infection, and provided the guide for the development of optimal multisubunit vaccines against C. trachomatis infection.     

Chlamydia trachomatis infection: host immune responses and potential vaccines

Chlamydia trachomatis causes genital tract infections that affect men, women, and children on a global scale. This review focuses on innate and adaptive immune responses in the female reproductive tract (FRT) to genital tract infections with C. trachomatis. It covers C. trachomatis infections and highlights our current knowledge of genital tract infections, serovar distribution, infectious load, and clinical manifestations of these infections in women. The unique features of the immune system of the FRT will be discussed and will include a review of our current knowledge of innate and adaptive immunity to chlamydial infections at this mucosal site. The use of animal models to study the pathogenesis of, and immunity to, Chlamydia infection of the female genital tract will also be discussed and a review of recent immunization and challenge experiments in the murine model of chlamydial FRT infection will be presented.     

Reduced Live Organism Recovery and Lack of Hydrosalpinx in Mice Infected with Plasmid-Free Chlamydia muridarum

Plasmid-free Chlamydia trachomatis and Chlamydia muridarum fail to induce severe pathology. To evaluate whether the attenuated pathogenicity is due to insufficient infection or inability of the plasmidless chlamydial organisms to trigger pathological responses, we compared plasmid-competent and plasmid-free C. muridarum infections in 5 different strains of mice. All 5 strains developed hydrosalpinx following intravaginal inoculation with plasmid-competent, but not inoculation with plasmid-free, C. muridarum. The lack of hydrosalpinx induction by plasmid-free C. muridarum correlated with significantly reduced live organism recovery from the lower genital tract and shortened infection in the upper genital tract. The plasmid-free C. muridarum organisms failed to induce hydrosalpinx even when the organisms were directly inoculated into the oviduct via an intrabursal injection, which was accompanied by significantly reduced survival of the plasmidless organisms in the genital tracts. Furthermore, plasmid-competent C. muridarum organisms after UV inactivation were no longer able to induce hydrosalpinx even when directly delivered into the oviduct at a high dose. Together, these observations suggest that decreased survival of and shortened infection with plasmid-free C. muridarum may contribute significantly to its attenuated pathogenicity. We conclude that adequate live chlamydial infection in the oviduct may be necessary to induce hydrosalpinx.     

In Vivo and Ex Vivo Imaging Reveals a Long-Lasting Chlamydial Infection in the Mouse Gastrointestinal Tract following Genital Tract Inoculation

Intravaginal infection with Chlamydia muridarum in mice can ascend to the upper genital tract, resulting in hydrosalpinx, a pathological hallmark for tubal infertility in women infected with C. trachomatis. Here, we utilized in vivo imaging of C. muridarum infection in mice following an intravaginal inoculation and confirmed the rapid ascent of the chlamydial organisms from the lower to upper genital tracts. Unexpectedly, the C. muridarum-derived signal was still detectable in the abdominal area 100 days after inoculation. Ex vivo imaging of the mouse organs revealed that the long-lasting presence of the chlamydial signal was restricted to the gastrointestinal (GI) tract, which was validated by directly measuring the chlamydial live organisms and genomes in the same organs. The C. muridarum organisms spreading from the genital to the GI tracts were detected in different mouse strains and appeared to be independent of oral or rectal routes. Mice prevented from orally taking up excretions also developed the long-lasting GI tract infection. Inoculation of C. muridarum directly into the upper genital tract, which resulted in a delayed vaginal shedding of live organisms, accelerated the chlamydial spreading to the GI tract. Thus, we have demonstrated that the genital tract chlamydial organisms may use a systemic route to spread to and establish a long-lasting infection in the GI tract. The significance of the chlamydial spreading from the genital to GI tracts is discussed.     

Role of NK Cells in Early Host Response to Chlamydial Genital Infection

The cell-mediated immune response has been documented to be the major protective immune mechanism in mice infected genitally with the agent of mouse pneumonitis (MoPn), a biovar of Chlamydia trachomatis. Moreover, there is strong evidence to indicate that gamma interferon (IFN-γ) is a major effector mechanism of the cell-mediated immune response. Previous studies from this laboratory have also reported that the dominant cell population in the genital tract is the CD4 Th1 population. When experiments were performed by the enzyme-linked immunospot assay, high numbers of cells producing IFN-γ were found in the genital tract, concomitant with resolution of the infection; however, in addition, an increase in IFN-γ-producing cells which were CD4⁻ was seen early in the infection. Since natural killer (NK) cells produce IFN-γ and have been found to participate in the early responses in other infections, we hypothesized that NK cells are responsible for early IFN-γ production in the murine chlamydial model. NK cells were quantified by the standard YAC-1 cytotoxicity assay and were found to appear in the genital tract as early as 12 h after intravaginal infection with MoPn. The cells were confirmed to be NK cells by abrogation of YAC-1 cell cytotoxicity by treatment in vitro and in vivo with anti-asialo-GM1. The early IFN-γ response could also be depleted by treatment with anti-asialo-GM1, indicating that NK cells were responsible for the production of this cytokine. Of interest was our observation that depletion of NK cells also exacerbated the course of infection in the mice and elicited a Th2 response, as indicated by a marked increase in immunoglobulin G1 antibody. Thus, these data demonstrate that NK cells are not only responsible for the production of IFN-γ early in the course of chlamydial genital tract infection but are also, via IFN-γ, a significant factor in the development of the Th1 CD4 response and in the control of the infection.     

Caspase-1 contributes to Chlamydia trachomatis-induced upper urogenital tract inflammatory pathologies without affecting the course of infection

Chlamydia trachomatis infection induces inflammatory pathologies in the upper genital tract, potentially leading to ectopic pregnancy and infertility in the affected women. Caspase-1 is required for processing and release of the inflammatory cytokines interleukin-1β (IL-1β), IL-18, and possibly IL-33. In the present study, we evaluated the role of caspase-1 in chlamydial infection and pathogenesis. Although chlamydial infection induced caspase-1 activation and processing of IL-1β, mice competent and mice deficient in caspase-1 experienced similar courses of chlamydial infection in their urogenital tracts, suggesting that Chlamydia-activated caspase-1 did not play a significant role in resolution of chlamydial infection. However, when genital tract tissue pathologies were examined, the caspase-1-deficient mice displayed much reduced inflammatory damage. The reduction in inflammation was most obvious in the fallopian tube tissue. These observations demonstrated that although caspase-1 is not required for controlling chlamydial infection, caspase-1-mediated responses can exacerbate the Chlamydia-induced inflammatory pathologies in the upper genital tract, suggesting that the host caspase-1 may be targeted for selectively attenuating chlamydial pathogenicity without affecting the host defense against chlamydial infection.     

Route of Infection That Induces a High Intensity of Gamma Interferon-Secreting T Cells in the Genital Tract Produces Optimal Protection against Chlamydia trachomatis Infection in Mice

The induction of local T helper type 1 (Th1)-mediated cellular immunity is crucial for resistance of mice to genital infection by the obligate intracellular bacterium Chlamydia trachomatis. We tested the hypothesis that the route of immunization that elicits relatively high numbers of chlamydia-specific, gamma interferon (IFN-γ)-secreting T lymphocytes (ISTLs) in the genital tract would induce optimal protective immunity against reinfection. Female BALB/c mice were infected intravaginally (i.v.), intranasally (i.n.), orally (p.o.), or subcutaneously (s.c.) with C. trachomatis. At days 7, 14, 21, and 28 postinfection, T cells isolated from the genital tract tissues were restimulated with chlamydial antigen in vitro, and the amounts of IFN-γ induced were measured by a sandwiched enzyme-linked immunosorbent assay method. At day 7 postinfection, i.n.- and i.v.-immunized mice had high levels of chlamydia-specific ISTLs in their genital tracts (203.58 ± 68.1 and 225.5 ± 12.1 pg/ml, respectively). However, there were no detectable ISTLs in the genital tracts of p.o.- or s.c.-infected mice. When preinfected mice were challenged i.v. 70 days later, animals preexposed by the i.n. route were highly resistant to reinfection, with greatly reduced chlamydial burden, and suffered an attenuated infection that resolved by day 6 postchallenge. Animals preexposed by the i.v. route were modestly protected, whereas p.o. and s.c. groups were indistinguishable in this regard from control mice. The resistance of i.n.-immunized mice (and to some extent the i.v.-exposed mice) to reinfection was associated with early appearance (within 24 h) of high levels of genital ISTLs compared with mice preinfected by other routes. Furthermore, although i.n. and i.v.-immunized mice had comparable levels of chlamydia-specific immunoglobulin A (IgA) antibodies in their vaginal washes, the levels of IgG2a were four- sixfold higher in i.n.-immunized mice than in any of the other groups. The results suggested that immunization routes that foster rapid induction of vigorous genital mucosal cell-mediated immune (CMI) effectors (e.g., IFN-γ), the CMI-associated humoral effector, IgG2a, and to some extent secretory IgA produce protective immunity against chlamydial genital infection. Therefore, i.n. immunization is a potential delivery route of choice in the development of a vaccine against Chlamydia.     

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

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

Hypothesis: Chlamydia trachomatis infection of the female genital tract is controlled by Type 2 immunity

Chlamydia trachomatis is an obligate intracellular bacterium sexually transmitted to more than 90 million individuals each year. As this level of infectivity implies, C. trachomatis is a successful human parasite; a success facilitated by its ability to cause asymptomatic infection. Host defense against C. trachomatis in the female genital tract is not well defined, but current dogma suggests infection is controlled largely by T_H1 immunity. Conversely, it is well established that T_H2 immunity controls allergens, helminths, and other extracellular pathogens that cause repetitive or persistent T cell stimulation but do not induce the exuberant inflammation that drives T_H1 and T_H17 immunity. As C. trachomatis persists in female genital tract epithelial cells but does not elicit over tissue inflammation, we now posit that defense is maintained by Type 2 immune responses that control bacterial growth but minimize immunopathological damage to vital reproductive tract anatomy. Evaluation of this hypothesis may uncover novel mechanisms by which Type 2 immunity can control growth of C. trachomatis and other intracellular pathogens, while confirmation that T_H2 immunity was selected by evolution to control C. trachomatis infection in the female genital tract will transform current research, now focused on developing vaccines that elicit strong, and therefore potentially tissue destructive, Chlamydia-specific T_H1 immunity.     

In Vitro Passage Selects for Chlamydia muridarum with Enhanced Infectivity in Cultured Cells but Attenuated Pathogenicity in Mouse Upper Genital Tract

Although modern Chlamydia muridarum has been passaged for decades, there are no reports on the consequences of serial passage with strong selection pressure on its fitness. In order to explore the potential for Pasteurian selection to induce genomic and phenotypic perturbations to C. muridarum, a starter population was passaged in cultured cells for 28 generations without standard infection assistance. The resultant population, designated CMG28, displays markedly reduced in vitro dependence on centrifugation for infection and low incidence and severity of upper genital tract pathology following intravaginal inoculation into mice compared to the parental C. muridarum population, CMG0. Deep sequencing of CMG0 and CMG28 revealed novel protein variants in the hypothetical genes TC0237 (Q117E) and TC0668 (G322R). In vitro attachment assays of isogenic plaque clone pairs with mutations in either TC0237 and TC0668 or only TC0237 reveal that TC0237(Q117E) is solely responsible for enhanced adherence to host cells. Paradoxically, double mutants, but not TC0237(Q117E) single mutants, display severely attenuated in vivo pathogenicity. These findings implicate TC0237 and TC0668 as novel genetic factors involved in chlamydial attachment and pathogenicity, respectively, and show that serial passage under selection pressure remains an effective tool for studying Chlamydia pathogenicity.     

Chlamydia muridarum Major Outer Membrane Protein‐Specific Antibodies Inhibit In Vitro Infection but Enhance Pathology In Vivo

Citation Cunningham KA, Carey AJ, Hafner L, Timms P, Beagley KW. Chlamydia muridarum major outer membrane protein‐specific antibodies inhibit in vitro infection but enhance pathology in vivo. Am J Reprod Immunol 2011; 65: 118–126 Problem Chlamydia trachomatis is a significant worldwide health problem, and the often‐asymptomatic disease can result in infertility. To develop a successful vaccine, a complete understanding of the immune response to chlamydial infection and development of genital tract pathology is required. Method of Study We utilized the murine genital model of chlamydial infection. Mice were immunized with chlamydial major outer membrane protein, and vaginal lavage was assessed for the presence of neutralizing antibodies. These samples were then pre‐incubated with Chlamydia muridarum and administered to the vaginal vaults of immune‐competent female BALB/c mice to determine the effect on infection. Results The administration of C. muridarum in conjunction with neutralizing antibodies reduced the numbers of mice infected, but a surprising finding was that this accelerated the development of severe oviduct pathology. Conclusion Antibodies play an under‐recognized role in chlamydial infection and pathology development, which possibly involves interaction with Th1 immunity.     

Beta Interferon Is Produced by Chlamydia trachomatis-Infected Fibroblast-Like Synoviocytes and Inhibits Gamma Interferon-Induced HLA-DR Expression

Infection of fibroblast-like synovial cells with Chlamydia trachomatis (serotype D strain IC Cal 8) in culture induced the secretion of beta interferon (IFN-β). Chlamydial infection inhibited IFN-γ-induced expression of HLA-DR antigen in the cells. Addition of IFN-β antibody directly to infected cultures mitigated HLA-DR inhibition, suggesting involvement of produced IFN-β.     

Hypothesis: Chlamydia trachomatis infection of the female genital tract is controlled by Type 2 immunity

Chlamydia trachomatis is an obligate intracellular bacterium sexually transmitted to more than 90 million individuals each year. As this level of infectivity implies, C. trachomatis is a successful human parasite; a success facilitated by its ability to cause asymptomatic infection. Host defense against C. trachomatis in the female genital tract is not well defined, but current dogma suggests infection is controlled largely by T_H1 immunity. Conversely, it is well established that T_H2 immunity controls allergens, helminths, and other extracellular pathogens that cause repetitive or persistent T cell stimulation but do not induce the exuberant inflammation that drives T_H1 and T_H17 immunity. As C. trachomatis persists in female genital tract epithelial cells but does not elicit over tissue inflammation, we now posit that defense is maintained by Type 2 immune responses that control bacterial growth but minimize immunopathological damage to vital reproductive tract anatomy. Evaluation of this hypothesis may uncover novel mechanisms by which Type 2 immunity can control growth of C. trachomatis and other intracellular pathogens, while confirmation that T_H2 immunity was selected by evolution to control C. trachomatis infection in the female genital tract will transform current research, now focused on developing vaccines that elicit strong, and therefore potentially tissue destructive, Chlamydia-specific T_H1 immunity.     

Sulfated Polysaccharides and a Synthetic Sulfated Polymer Are Potent Inhibitors of Chlamydia trachomatis Infectivity In Vitro but Lack Protective Efficacy in an In Vivo Murine Model of Chlamydial Genital Tract Infection

Heparin, dextran sulfate, pentosan polysulfate, and a sulfated synthetic copolymer of acrylic acid and vinyl alcohol were shown to be potent inhibitors of Chlamydia trachomatis infectivity for cultured human epithelial cells. Despite their potent antichlamydial activity in vitro, neither heparin nor dextran sulfate was effective in inhibiting the infectivity of C. trachomatis in a murine model of chlamydial infection of the female genital tract.     

Lack of Long-Lasting Hydrosalpinx in A/J Mice Correlates with Rapid but Transient Chlamydial Ascension and Neutrophil Recruitment in the Oviduct following Intravaginal Inoculation with Chlamydia muridarum

Lower genital tract infection with Chlamydia trachomatis and C. muridarum can induce long-lasting hydrosalpinx in the upper genital tract of women and female mice, respectively. However, A/J mice were highly resistant to induction of long-lasting hydrosalpinx by C. muridarum. We further compared host inflammatory responses and chlamydial infection courses between the hydrosalpinx-resistant A/J mice and CBA/J mice known to be susceptible to hydrosalpinx induction. Both mouse strains developed robust pyosalpinx during the acute phase followed by hydrosalpinx during the chronic phase. However, the hydrosalpinges disappeared in A/J mice by day 60 after infection, suggesting that some early hydrosalpinges are reversible. Although the overall inflammatory responses were indistinguishable between CBA/J and A/J mice, we found significantly more neutrophils in oviduct lumen of A/J mice on days 7 and 10, which correlated with a rapid but transient oviduct invasion by C. muridarum with a peak infection on day 7. In contrast, CBA/J mice developed a delayed and extensive oviduct infection. These comparisons have revealed an important role of the interactions of oviduct infection with inflammatory responses in chlamydial induction of long-lasting hydrosalpinx, suggesting that a rapid but transient invasion of oviduct by chlamydial organisms can prevent the development of the long-lasting hydrosalpinges.