IL-10 Overexpression Reduces the Protective Response of an Experimental Chlamydia abortus Vaccine in a Murine Model.

In ovine populations, the enzootic nature of Chlamydia abortus (C. abortus) is attributed to its capacity to establish persistent intracellular infections, which necessitate a cellular immune response mediated by interferon-gamma (IFN-γ) for effective resolution. In both natural hosts and murine models, interleukin-10 (IL-10) has been demonstrated to modulate the cellular immune response crucial for the eradication of C. abortus. During gestation, it has also been shown to play a role in preventing inflammatory damage to gestational tissues and foetal loss through the downregulation of pro-inflammatory cytokines. This paradigm can be key for events leading to a protective response towards an infectious abortion. Previous research successfully established a mouse model of chronic C. abortus infection using transgenic mice overexpressing IL-10 (IL-10tg), simulating the dynamics of chronic infection observed in non-pregnant natural host. This study aims to evaluate the efficacy of an experimental inactivated vaccine against C. abortus and to elucidate the immune mechanisms involved in protection during chronic infection using this model. Transgenic and wild-type (WT) control mice were immunized and subsequently challenged with C. abortus. Vaccine effectiveness and immune response were assessed via immunohistochemistry and cytokine serum levels over a 28-day period. Morbidity, measured by daily weight loss, was more pronounced in non-vaccinated transgenic IL-10 mice, though no mortality was observed in any group. Vaccinated control mice eliminated the bacterial infection by day 9 post-infection (p.i.), whereas presence of bacteria was noted in vaccinated transgenic IL-10 mice until day 28 p.i. Vaccination induced an early post-infection increase in IFN-γ production, but did not alter IL-10 production in transgenic mice. Histological analysis indicated suboptimal recruitment of inflammatory cells in vaccinated transgenic IL-10 mice compared to WT controls. In summary, the findings suggest that IL-10 overexpression in transgenic mice diminishes the protective efficacy of vaccination, confirming that this model can be useful for validating the efficacy of vaccines against intracellular pathogens such as C. abortus that require robust cell-mediated immunity.

Effect of Female Sex Hormones on the Immune Response against Chlamydia abortus and on Protection Conferred by an Inactivated Experimental Vaccine in a Mouse Model.

Mice are valuable models extensively used to test vaccine candidates against Chlamydia abortus and to clarify immunopathological mechanisms of the bacteria. As this pathogen has the ability to reactivate during pregnancy, it is important to deepen the knowledge and understanding of some of the effects of female hormones on immunity and vaccination. This study is aimed at describing the role of sex hormones in the pathology of OEA during chlamydial clearance using ovariectomised mice and also gaining an understanding of how 17ß-oestradiol or progesterone may impact the effectiveness of vaccination. Animals were treated with sex hormones and infected with C. abortus, and the kinetics of infection and immune response were analysed by means of bacterial isolation, histopathology, and immunohistochemistry. In a second phase of the study, protection conferred by an experimental vaccine after hormone treatment was assessed. Oestradiol showed a stimulatory effect on the immune response during infection, with a more efficient recruitment of macrophages and T-cells at the infection site. Furthermore, after vaccination, oestradiol-treated animals showed a stronger protection against infection, indicating that this hormone has a positive effect, stimulating a specific memory response to the pathogen.

Evaluation of the Efficacy of a New Commercially Available Inactivated Vaccine Against Ovine Enzootic Abortion.

Ovine enzootic abortion (OEA), caused by Chlamydia abortus, is an economically important disease in many countries. Inactivated vaccines have been used for many years as they induce immunity in sheep, although outbreaks of abortions have been described in vaccinated flocks. In addition, there is a commercially available live attenuated vaccine that provides good protective results. Recently however, reports question the attenuation of this vaccine and associate it with the appearance of outbreaks of OEA in vaccinated flocks. In the present study, a recently commercialized inactivated vaccine (INMEVA®; Laboratorios Hipra S.A., Amer, Spain) has been evaluated using mouse and sheep experimental models. In the mouse models (non-pregnant and pregnant models), the efficacy of INMEVA vaccine has been compared to an unvaccinated control group and to an experimental inactivated vaccine considered as a positive protection control (UMU vaccine). In the non- pregnant model, the UMU vaccine was more effective than the INMEVA vaccine regarding the impact on body weight or the presence of C. abortus in the liver, but both vaccinated groups (UMU and INMEVA) had significantly lower C. abortus in the liver compared to the control group. In the pregnant model in terms of reproductive failures, pups per mouse or the presence of C. abortus in the liver or uterus, no significant differences were found between both vaccines, inducing protection compared to the control group. In the ovine pregnant model, where INMEVA vaccine was compared only to an unvaccinated group, the results indicate that this new commercial vaccine is safe and provides a suitable level of protection against an experimental challenge with C. abortus. A 75% reduction in reproductive disorders, 55% reduction in animals with C. abortus shedding on day of parturition/abortion, and a significant reduction of the average amount of chlamydial shedding from parturition/abortion over the next 21 days was observed, in relation to the infected control group. The results suggest that this vaccine is adequate for the control and prevention of OEA; however, future studies are necessary to elucidate the type of protective immune response that it induces.

Development of an in vivo model of Chlamydia abortus chronic infection in mice overexpressing IL-10.

Chlamydia abortus, like other members of the family Chlamydiaceae, have a unique intracellular developmental cycle that is characterized by its chronic nature. Infection of a flock can remain undetected for months, until abortion occurs the following reproductive season but, to date, neither the location nor the mechanisms that maintain this latent phase are fully understood. Studies have shown that IL-10 produced as a response to certain micro-organisms sustains the intracellular survival of pathogens and increases host susceptibility to chlamydial infections. In order to induce a sustained infection C. abortus, transgenic mice that constitutively express IL-10 were infected and the immunological mechanisms that maintain infection in these mice were compared with the mechanisms of a resistant wild-type mouse strain. Viable bacteria could be detected in different tissues of transgenic mice up to 28 days after infection, as analysed by bacterial isolation and immunohistochemistry. Chronic infection in these mice was associated with an impaired recruitment of macrophages, decreased iNOS activity at the site of infection and a more diffuse distribution of inflammatory cells in the liver. This murine model can be of great help for understanding the immunological and bacterial mechanisms that lead to chronic chlamydial infections.

Pathogens of zoonotic and biological importance in roe deer (Capreolus capreolus): Seroprevalence in an agro-system population in France.

Antibody prevalence for several infectious and parasitic diseases in a population of roe deer (Capreolus capreolus) inhabiting a mixed agricultural landscape (south of France) has been analyzed. Serological analyses with ELISA in 245 animals captured from 2008 to 2012 has been performed. We found a high prevalence of Toxoplasma gondii (46.4%), Chlamydophila abortus (17.27%) and Coxiella burnetii (11.26%) compared to other studies in Europe. Seroprevalence varied strongly among years for T. gondii (27-91%), C. abortus (0-42%) and C. burnetii (0-27%). T. gondii prevalence was lower in juvenile females, compared to juvenile males and adults of both sexes. Other pathogens had low prevalences: Neospora caninum (1.56%), Bovine herpesvirus 1 (1.17%, 2008/09; 1.1%, 2010/11), Mycoplasma agalactiae (1.45%, 2009/10), Mycobacterium avium subsp. paratuberculosis (0.9%) and Slow viruses (CAEV-MVV) (0.15%, 2008/10; 0%, 2011/12). Antibodies to bluetongue virus and pestiviruses were not found in any individual.