Understanding Acquired Immunity to Chlamydia in the Female Reproductive Tract

Sexually transmitted infections (STIs) affect over 68 million people in the U.S.annually and are highly prevalent among young people. Antibiotic and antiviral drugs have widely been used to treat STIs in patients and this treatment strategy has led to the development of incurable multidrug resistant pathogens. Thus, there is an urgent need for the development of effective vaccines to control the transmission of STIs in the population. While vaccines have been developed to protect the public against some STIs such as Human Papilloma Virus, many other sexually transmitted pathogens such as Gonorrhea, Herpes Simplex Virus (HSV) and the intracellular bacterium Chlamydia Trachomatis, are uncontrolled in the population. Women are particularly vulnerable to such infections as these pathogens often wreak havoc on the female reproductive system. Indeed, Chlamydia trachomatis can cause pelvic inflammatory disease (PID), ectopic pregnancy, and even infertility in some women. Despite the striking threat of STIs to women’s health, our understanding of how immunity develops in the female reproductive tract (FRT) is incomplete. Much of our knowledge of immunity in the FRT derives from studies using mouse models of genital HSV and LCMV infections. These studies have highlighted an important role for memory T cells, especially those resident in the tissue (TRM) as well as local antibody secretion in the FRT for clearing viral infections. In addition, clusters of memory T cells and antigen presenting cells (APCs) termed memory lymphocyte clusters (MLCs) were shown to be vital for mounting secondary immune responses and clearance of HSV vi infection. Although there have been quite a few studies of viral FRT infections, very little is known about how immunity develops in the FRT after bacterial infections. Chlamydia muridarum (Cm) infects the upper female reproductive tract and is a great model to study intracellular bacterial infection and development of FRT pathology in mice. This pathogen replicates inside host epithelial cells and requires CD4 T cells for clearance of infection, complementing studies of human Chlamydia trachomatis infections in which resistance to infection correlates with interferon gamma production. Using Cm infection in mice, we sought to determine the immune requirements for secondary protection in the FRT. We first hypothesized that antigen-independent immunity could lead to local protection against FRT Chlamydia infection. To test this theory, we developed a pet shop mouse co-housing model at UC Davis based on previous work that established this method as a useful way to generate non-specific immunity against certain pathogens. This model consisted of co-housing inbred laboratory mice with “dirty” pet shop mice, which transmitted endemic pathogens to the lab mice. The goal of this model was to better recapitulate an experienced human immune system in laboratory mice. After the cohousing period, the laboratory mice were challenged with Cm and the severity of infection was measured. Using the pet shop co-housing model, we did not detect any advantage of non-specific immunity on resistance to Chlamydia infection. Therefore, to achieve effective immunity against genital Chlamydia infection, antigen-specific immunity was likely required. The development of TRM and MLCs in the female reproductive tract has been observed after genital Cm infection much like genital HSV infection. Hence, we vii hypothesized that these immune factors were required for antigen-specific immunity to Chlamydia infection in the FRT. We tested the requirement of resident immunity for secondary protection using parabiosis surgery and found that resident immune memory was completely dispensable for local FRT protection against Chlamydia. Furthermore, resident immunity was irrelevant to secondary protection whether this immunity was generated through local intravaginal immunization or distal intranasal immunization. Experiments examining protection after intranasal immunization demonstrated that circulating immunity was completely protective against bacterial burden and the development of pathology after intravaginal rechallenge infection. CD4 T cells were required to control vaginal infection in intranasal immune mice, demonstrating that these lymphocytes were likely the main mediators of circulating immunity. The findings in this study have greatly clarified the required immune components for secondary immunity to Chlamydia infection of the female genital tract. In summary, this work advances our understanding of how immunity to a sexually transmitted bacterial pathogen develops in the female reproductive tract, a previously unaddressed gap in knowledge in the field

Diversity in the T cell response to Chlamydia-sum are better than one.

Chlamydia trachomatis is responsible for an increasing number of sexually transmitted infections in the United States and is a common cause of serious pathology in the female reproductive tract (FRT). Given the impact and incidence of these infections, the production of an effective Chlamydia vaccine is a public health priority. Mouse models of Chlamydia infection have been utilized to develop a detailed and mechanistic understanding of protective immunity in the FRT. These studies reveal that MHC class-II restricted Chlamydia-specific CD4 T cells are critical for primary bacterial clearance and provide effective protection against secondary infection in the FRT. Despite the clear importance of IFN- γ produced by CD4 Th1 cells, there are also suggestions of wider functional heterogeneity in the CD4 T cell response to Chlamydia infection. Understanding the role of this diversity in the CD4 T helper cell response in the FRT should allow a more nuanced view of CD4 T cell biology in the context of Chlamydia infection and may be critical for vaccine development. Here, we summarize our current understanding of CD4 T helper subsets in the clearance of Chlamydia and discuss some areas where knowledge needs to be further extended by additional experimentation

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

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

Cohousing with Dirty Mice Increases the Frequency of Memory T Cells and Has Variable Effects on Intracellular Bacterial Infection

The presence of memory lymphocytes in nonlymphoid tissues reflects prior immunological experience and can provide nonspecific defense against infection. In this study, we used a mouse cohousing approach to examine the effect of prior immunological experience on Salmonella and Chlamydia infection. As expected, cohousing of "dirty mice" with specific pathogen-free laboratory mice increased the frequency of effector memory T cells in laboratory mice and enhanced protection against systemic Listeria infection. In contrast, the course of systemic infection with Salmonella and mucosal infection with Chlamydia was largely unaffected by cohousing, despite enhanced frequencies of memory T cells. Thus, cohousing of laboratory mice reliably increases the proportion of memory T cells in circulation, but can it have variable effects on pathogen clearance

CCR7 Deficiency Allows Accelerated Clearance of Chlamydia from the Female Reproductive Tract

Immune mechanisms responsible for pathogen clearance from the female reproductive tract (FRT) are incompletely defined; in particular, the contribution of lymphocyte trafficking to this process is unclear. CCR7-deficient mice have profoundly altered lymphocyte recirculation and display ectopic formation of lymphocyte aggregates within mucosal nonlymphoid tissues, including the FRT. In this study, we investigated how altered lymphocyte distribution in CCR7-deficient mice would affect host responses to Chlamydia muridarum within the reproductive tract. As expected, CCR7-deficient mice exhibited reduced lymphocyte trafficking to lymph nodes and a corresponding increase in T cell populations within the FRT. After intravaginal infection with Chlamydia, CCR7-deficient mice displayed markedly reduced Ag-specific CD4 T cell responses within the local draining iliac lymph nodes, yet robust Th1 and Th17 responses were prominent in the FRT. In addition, Chlamydia-specific Ab responses were dysregulated in CCR7-deficient mice, displaying an unexpected increase in the systemic IgA responses. Importantly, prominent mucosal immune responses in CCR7-deficient mice increased the efficiency of bacteria clearance from the FRT while reducing tissue-associated inflammation and pathology. Thus, increased numbers of lymphocytes within the FRT result in pathogen clearance with reduced immune-mediated pathology

Unexpected Role of CD8 T Cells in Accelerated Clearance of Salmonella enterica Serovar Typhimurium from H-2 Congenic mice.

Salmonella infection can cause gastroenteritis in healthy individuals or a serious, systemic infection in immunocompromised patients and has a global impact. CD4 Th1 cells represent the main lymphocyte population that participates in bacterial clearance during both primary and secondary infections in mice of the H-2b haplotype. Previous studies have used congenic mice to examine the function of major histocompatibility complex (MHC) molecules in elimination of this pathogen from the host. In this study, we further characterized the ability of H-2b, H-2k, and H-2u molecules to influence adaptive immunity to Salmonella in MHC congenic mice. By depleting different cell populations during infection, we unexpectedly found that CD8 T cells, in addition to CD4 T cells, play a major role in accelerated clearance of bacteria from H-2k congenic hosts. Our data suggest that CD8 T cells accelerate clearance in some MHC congenic mouse strains and could therefore represent an unexpected contributor to the protective efficacy of Salmonella vaccines outside the typical studies in C57BL/6 mice

Circulating immunity protects the female reproductive tract from Chlamydia infection

Anatomical positioning of memory lymphocytes within barrier tissues accelerates secondary immune responses and is thought to be essential for protection at mucosal surfaces. However, it remains unclear whether resident memory in the female reproductive tract (FRT) is required for Chlamydial immunity. Here, we describe efficient generation of tissue-resident memory CD4 T cells and memory lymphocyte clusters within the FRT after vaginal infection with Chlamydia Despite robust establishment of localized memory lymphocytes within the FRT, naïve mice surgically joined to immune mice, or mice with only circulating immunity following intranasal immunization, were fully capable of resisting Chlamydia infection via the vaginal route. Blocking the rapid mobilization of circulating memory CD4 T cells to the FRT inhibited this protective response. These data demonstrate that secondary protection in the FRT can occur in the complete absence of tissue-resident immune cells. The ability to confer robust protection to barrier tissues via circulating immune memory provides an unexpected opportunity for vaccine development against infections of the FRT