IgG exacerbates genital chlamydial pathology in females by enhancing pathogenic CD8+ T cell responses

Chlamydia trachomatis infections are an important sexually transmitted infection that can lead to inflammation, scarring and hydrosalpinx/infertility. However, infections are commonly clinically asymptomatic and do not receive treatment. The underlying cause of asymptomatic immunopathology remains unknown. Here, we demonstrate that IgG produced during male infection enhanced the incidence of immunopathology and infertility in females. Human endocervical cells expressing the neonatal Fc Receptor (FcRn) increased translocation of human IgG-opsonized C. trachomatis. Using total IgG purified from infected male mice, we opsonized C. muridarum and then infected female mice, mimicking sexual transmission. Following infection, IgG-opsonized Chlamydia was found to transcytose the epithelial barrier in the uterus, where it was phagocytosed by antigen-presenting cells (APCs) and trafficked to the draining lymph nodes. APCs then expanded both CD4+ and CD8+ T cell populations and caused significantly more infertility in female mice infected with non-opsonized Chlamydia. Enhanced phagocytosis of IgG-opsonized Chlamydia significantly increased pro-inflammatory signalling and T cell proliferation. As IgG is transcytosed by FcRn, we utilized FcRn-/- mice and observed that shedding kinetics of Chlamydia were only affected in FcRn-/- mice infected with IgG-opsonized Chlamydia. Depletion of CD8+ T cells in FcRn-/- mice lead to a significant reduction in the incidence of infertility. Taken together, these data demonstrate that IgG seroconversion during male infection can amplify female immunopathology, dependent on FcRn transcytosis, APC differentiation and enhanced CD8 T cell responses.

Origin and evolutionary malleability of T cell receptor α diversity

Lymphocytes of vertebrate adaptive immune systems acquired the capability to assemble, from split genes in the germline, billions of functional antigen receptors^1-3. These receptors show specificity; unlike the broadly tuned receptors of the innate system, antibodies (Ig) expressed by B cells, for instance, can accurately distinguish between the two enantiomers of organic acids⁴, whereas T cell receptors (TCRs) reliably recognize single amino acid replacements in their peptide antigens⁵. In developing lymphocytes, antigen receptor genes are assembled from a comparatively small set of germline-encoded genetic elements in a process referred to as V(D)J recombination^6,7. Potential self-reactivity of some antigen receptors arising from the quasi-random somatic diversification is suppressed by several robust control mechanisms^8-12. For decades, scientists have puzzled over the evolutionary origin of somatically diversifying antigen receptors^13-16. It has remained unclear how, at the inception of this mechanism, immunologically beneficial expanded receptor diversity was traded against the emerging risk of destructive self-recognition. Here we explore the hypothesis that in early vertebrates, sequence microhomologies marking the ends of recombining elements became the crucial targets of selection determining the outcome of non-homologous end joining-based repair of DNA double-strand breaks generated during RAG-mediated recombination. We find that, across the main clades of jawed vertebrates, TCRα repertoire diversity is best explained by species-specific extents of such sequence microhomologies. Thus, selection of germline sequence composition of rearranging elements emerges as a major factor determining the degree of diversity of somatically generated antigen receptors.

Genetic landscape of T cells identifies synthetic lethality for T-ALL

To capture the global gene network regulating the differentiation of immature T cells in an unbiased manner, large-scale forward genetic screens in zebrafish were conducted and combined with genetic interaction analysis. After ENU mutagenesis, genetic lesions associated with failure of T cell development were identified by meiotic recombination mapping, positional cloning, and whole genome sequencing. Recessive genetic variants in 33 genes were identified and confirmed as causative by additional experiments. The mutations affected T cell development but did not perturb the development of an unrelated cell type, growth hormone-expressing somatotrophs, providing an important measure of cell-type specificity of the genetic variants. The structure of the genetic network encompassing the identified components was established by a subsequent genetic interaction analysis, which identified many instances of positive (alleviating) and negative (synthetic) genetic interactions. Several examples of synthetic lethality were subsequently phenocopied using combinations of small molecule inhibitors. These drugs not only interfered with normal T cell development, but also elicited remission in a model of T cell acute lymphoblastic leukaemia. Our findings illustrate how genetic interaction data obtained in the context of entire organisms can be exploited for targeted interference with specific cell types and their malignant derivatives.

Antigen receptor repertoires of one of the smallest known vertebrates

The rules underlying the structure of antigen receptor repertoires are not yet fully defined, despite their enormous importance for the understanding of adaptive immunity. With current technology, the large antigen receptor repertoires of mice and humans cannot be comprehensively studied. To circumvent the problems associated with incomplete sampling, we have studied the immunogenetic features of one of the smallest known vertebrates, the cyprinid fish Paedocypris sp. "Singkep" ("minifish"). Despite its small size, minifish has the key genetic facilities characterizing the principal vertebrate lymphocyte lineages. As described for mammals, the frequency distributions of immunoglobulin and T cell receptor clonotypes exhibit the features of fractal systems, demonstrating that self-similarity is a fundamental property of antigen receptor repertoires of vertebrates, irrespective of body size. Hence, minifish achieve immunocompetence via a few thousand lymphocytes organized in robust scale-free networks, thereby ensuring immune reactivity even when cells are lost or clone sizes fluctuate during immune responses.

Cytidine deaminase 2 is required for VLRB antibody gene assembly in lampreys

The antibodies of jawless vertebrates consist of leucine-rich repeat arrays encoded by somatically assembled VLRB genes. It is unknown how the incomplete germline VLRB loci are converted into functional antibody genes during B lymphocyte development in lampreys. In Lampetra planeri larvae lacking the cytidine deaminase CDA2 gene, VLRB assembly fails, whereas the T lineage-associated VLRA and VLRC antigen receptor gene assemblies occur normally. Thus, CDA2 acts in a B cell lineage-specific fashion to support the somatic diversification of VLRB antibody genes. CDA2 is closely related to activation-induced cytidine deaminase (AID), which is essential for the elaboration of immunoglobulin gene repertoires in jawed vertebrates. Our results thus identify a convergent mechanism of antigen receptor gene assembly and diversification that independently evolved in the two sister branches of vertebrates.

Lymphocyte-Specific Function of the DNA Polymerase Epsilon Subunit Pole3 Revealed by Neomorphic Alleles

Immunodeficiencies are typically caused by loss-of-function mutations in lymphocyte-specific genes. Occasionally, mutations in ubiquitous general-purpose factors, including those affecting essential components of the DNA polymerase epsilon (POLE) holoenzyme, have cell-type-specific consequences. POLE3, one of the four components of the POLE holoenzyme, features a histone fold domain and a unique acidic C terminus, making it a particularly attractive candidate mediating cell type-specific activities of POLE. Mice lacking Pole3 survive up to late embryonic stages, indicating that this subunit is dispensable for DNA replication. The phenotypes of viable hypomorphic and neomorphic alleles are surprisingly tissue restricted and reveal a stage-specific function of the histone fold domain of Pole3 during T and B cell development. Gradual introduction of positively charged residues into the acidic C terminus leads to peripheral lymphopenia of increasing severity. Our findings serve as a paradigm to understand the molecular basis of cell-type-specific non-replicative functions of the ubiquitous POLE complex.

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

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

Forward Genetic Screens in Zebrafish Identify Pre-mRNA-Processing Pathways Regulating Early T Cell Development

Lymphocytes represent basic components of vertebrate adaptive immune systems, suggesting the utility of non-mammalian models to define the molecular basis of their development and differentiation. Our forward genetic screens in zebrafish for recessive mutations affecting early T cell development revealed several major genetic pathways. The identification of lineage-specific transcription factors and specific components of cytokine signaling and DNA replication and/or repair pathways known from studies of immunocompromised mammals provided an evolutionary cross-validation of the screen design. Unexpectedly, however, genes encoding proteins required for pre-mRNA processing were enriched in the collection of mutants identified here. In both zebrafish and mice, deficiency of the splice regulator TNPO3 impairs intrathymic T cell differentiation, illustrating the evolutionarily conserved and cell-type-specific functions of certain pre-mRNA-processing factors for T cell development.

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Forward genetic screens identify mutations affecting zebrafish T cell development

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Identification of il7r, jak3, and pole1 mutations validates specificity of screen design

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Mutations in pre-mRNA-processing factor genes reveal evolutionarily conserved pathway

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In zebrafish and mice, TNPO3 deficiency impairs T cell differentiation

Multistage vaccines containing outer membrane, type III secretion system and inclusion membrane proteins protects against a Chlamydia genital tract infection and pathology

Pathogens with a complex lifecycles can effectively evade host immunity in part due to each developmental stage expressing unique sets of antigens. Multisubunit vaccines incorporating signature antigens reflecting distinct developmental stages (multistage vaccines) have proven effective against viral, bacterial and parasitic infection at preventing pathogen evasion of host immunity. Chlamydia trachomatis is characterized by a biphasic extra/intracellular developmental cycle and an acute/persistent (latent) metabolic state; hence a multistage vaccine may prevent immune evasion and enhance clearance. Here we tested the efficacy of a multistage vaccine containing outer membrane (MOMP and PmpG), type three secretion system (T3SS) (CdsF and TC0873) and inclusion membrane proteins (IncA and TC0500) in mice against an intravaginal challenge with Chlamydia muridarum. Comparison of single (eg. MOMP) and double antigen vaccines (eg. MOMP and PmpG), largely targeting the extracellular stage, elicited significant yet comparable protection against vaginal shedding when compared to unimmunized control mice. Utilization of different adjuvants (ISCOMATRIX - IMX, PCEP/polyI:C/IDR1002 - VIDO, CTA1-DD and ADVAX) and numerous immunization routes (subcutaneous - SQ and intranasal - IN) further enhanced protection against infection. However, a multistage vaccine elicited significantly greater protection against vaginal shedding and upper genital tract pathology than vaccines targeting only extra- or intracellular stages. This indicates that protection elicited by a vaccine targeting extracellular chlamydial antigens could be improved by including chlamydial antigen expressed during intracellular phase.

Chlamydial infection enhances expression of the polymeric immunoglobulin receptor (pIgR) and transcytosis of IgA

PROBLEM

The pIgR mediates transport of IgA into the lumen of mucosal tissues preventing pathogenic infection. Despite this, the expression of pIgR during chlamydial infections of the male and female reproductive tracts remains poorly understood.

METHOD OF STUDY

The expression of pIgR in response to hormone cycling or over the course of chlamydial infection was determined in vitro and in vivo by Western blot or immunohistochemistry.

RESULTS

PIgR was upregulated in response to Chlamydia spp. infection of human epithelia, in both male and female mouse reproductive tracts. PIgR expression was found to be highest during estrus in the cervicovaginal and uterine epithelia and lowest during diestrus or following hormonal synchronization with Depo-Provera. Chlamydial infection of mice mediates upregulation of pIgR and transcytosis of IgA into the lumen.

CONCLUSIONS

Our results suggest that chlamydial infection enhances IgA secretion and pIgR expression by epithelia in the lower reproductive tracts of females and males, and hormone synchronization downregulates pIgR expression and transcytosis of IgA prior to challenge.

Induction of partial immunity in both males and females is sufficient to protect females against sexual transmission of Chlamydia

Sexually transmitted Chlamydia trachomatis causes infertility, and because almost 90% of infections are asymptomatic, a vaccine is required for its eradication. Mathematical modeling studies have indicated that a vaccine eliciting partial protection (non-sterilizing) may prevent Chlamydia infection transmission, if administered to both sexes before an infection. However, reducing chlamydial inoculum transmitted by males and increasing infection resistance in females through vaccination to elicit sterilizing immunity has yet to be investigated experimentally. Here we show that a partially protective vaccine (chlamydial major outer membrane protein (MOMP) and ISCOMATRIX (IMX) provided sterilizing immunity against sexual transmission between immunized mice. Immunizing male or female mice before an infection reduced chlamydial burden and disease development, but did not prevent infection. However, infection and inflammatory disease responsible for infertility were absent in 100% of immunized female mice challenged intravaginally with ejaculate collected from infected immunized males. In contrast to the sterilizing immunity generated following recovery from a previous chlamydial infection, protective immunity conferred by MOMP/IMX occurred independent of resident memory T cells. Our results demonstrate that vaccination of males or females can further protect the opposing sex, whereas vaccination of both sexes can synergize to elicit sterilizing immunity against Chlamydia sexual transmission.

High Chlamydia Burden Promotes Tumor Necrosis Factor-Dependent Reactive Arthritis in SKG Mice

OBJECTIVE

Chlamydia trachomatis is a sexually transmitted obligate intracellular pathogen that causes inflammatory reactive arthritis, spondylitis, psoriasiform dermatitis, and conjunctivitis in some individuals after genital infection. The immunologic basis for this inflammatory response in susceptible hosts is poorly understood. As ZAP-70(W163C) -mutant BALB/c (SKG) mice are susceptible to spondylo-arthritis after systemic exposure to microbial β-glucan, we undertook the present study to compare responses to infection with Chlamydia muridarum in SKG mice and BALB/c mice.

METHODS

After genital or respiratory infection with C muridarum, conjunctivitis and arthritis were assessed clinically, and eye, skin, and joint specimens were analyzed histologically. Chlamydial major outer membrane protein antigen-specific responses were assessed in splenocytes. Treg cells were depleted from FoxP3-DTR BALB/c or SKG mice, and chlamydial DNA was quantified by polymerase chain reaction.

RESULTS

Five weeks after vaginal infection with live C muridarum, arthritis, spondylitis, and psoriasiform dermatitis developed in female SKG mice, but not in BALB/c mice. Inflammatory bowel disease did not occur in mice of either strain. The severity of inflammatory disease was correlated with C muridarum inoculum size and vaginal burden postinoculation. Treatment with combination antibiotics starting 1 day postinoculation prevented disease. Chlamydial antigen was present in macrophages and spread from the infection site to lymphoid organs and peripheral tissue. In response to chlamydial antigen, production of interferon-γ and interleukin-17 was impaired in T cells from SKG mice but tumor necrosis factor (TNF) responses were exaggerated, compared to findings in T cells from BALB/c mice. Unlike previous observations in arthritis triggered by β-glucan, no autoantibodies developed. Accelerated disease triggered by depletion of Treg cells was TNF dependent.

CONCLUSION

In the susceptible SKG strain, Chlamydia-induced reactive arthritis develops as a result of deficient intracellular pathogen control, with antigen-specific TNF production upon dissemination of antigen, and TNF-dependent inflammatory disease.

Chlamydia pneumoniae and Chlamydia Trachomatis Infection Differentially Modulates Human Dendritic Cell Line (MUTZ) Differentiation and Activation

Chlamydia trachomatis and Chlamydia pneumoniae are important human pathogens that infect the urogenital/anorectal and respiratory tracts, respectively. Whilst the ability of these bacteria to infect epithelia is well defined, there is also considerable evidence of infection of leucocytes, including dendritic cells (DCs). Using a human dendritic cell line (MUTZ), we demonstrate that the infection and replication of chlamydiae inside DCs is species and serovar specific and that live infection with C. pneumoniae is required to upregulate costimulatory markers CD80, CD83 and human leucocyte antigen (HLA)-DR on MUTZ cells, as well as induce secretion of interleukin (IL)-2, IL-6, IL-8, IL-12 (p70), interferon-gamma and tumour necrosis factor-alpha Conversely, C. trachomatis serovar D failed to upregulate DC costimulatory markers, but did induce secretion of high concentrations of IL-8. Interestingly, we also observed that infection of MUTZ cells with C. pneumoniae or C. trachomatis serovar L2, whilst not replicative, remained infectious and upregulated lymph node migratory marker CCR7 mRNA. Taken together, these data confirm the findings of other groups using primary DCs and demonstrate the utility of MUTZ cells for further studies of chlamydial infection.

Evaluation of intra- and extra-epithelial secretory IgA in chlamydial infections

Immunoglobulin A is an important mucosal antibody that can neutralize mucosal pathogens by either preventing attachment to epithelia (immune exclusion) or alternatively inhibit intra-epithelial replication following transcytosis by the polymeric immunoglobulin receptor (pIgR). Chlamydia trachomatis is a major human pathogen that initially targets the endocervical or urethral epithelium in women and men, respectively. As both tissues contain abundant secretory IgA (SIgA) we assessed the protection afforded by IgA targeting different chlamydial antigens expressed during the extra- and intra-epithelial stages of infection. We developed an in vitro model using polarizing cells expressing the murine pIgR together with antigen-specific mouse IgA, and an in vivo model using pIgR(-/-) mice. Secretory IgA targeting the extra-epithelial chlamydial antigen, the major outer membrane protein, significantly reduced infection in vitro by 24% and in vivo by 44%. Conversely, pIgR-mediated delivery of IgA targeting the intra-epithelial inclusion membrane protein A bound to the inclusion but did not reduce infection in vitro or in vivo. Similarly, intra-epithelial IgA targeting the secreted protease Chlamydia protease-like activity factor also failed to reduce infection. Together, these data suggest the importance of pIgR-mediated delivery of IgA targeting extra-epithelial, but not intra-epithelial, chlamydial antigens for protection against a genital tract infection.

The mouse model of Chlamydia genital tract infection: a review of infection, disease, immunity and vaccine development

Chlamydia trachomatis is the most common sexually transmitted bacterial infection worldwide. The impact of this pathogen on human reproduction has intensified research efforts to better understand chlamydial infection and pathogenesis. Whilst there are animal models available that mimic many aspects of human chlamydial infection, the mouse is regarded as the most practical and widely used of the models. Studies in mice have greatly contributed to our understanding of the host-pathogen interaction and provided an excellent medium for evaluating vaccines. Here we explore the advantages and disadvantages of all animal models of chlamydial genital tract infection, with a focus on the murine model and what we have learnt from it so far.