8 research outputs found
Defining immune function and identifying correlates of protection against Chlamydia abortus in sheep
Chlamydia abortus is an obligate intracellular bacterial pathogen and is one of
the most common causes of infectious abortion in sheep world-wide. The
organism is responsible for the disease known as ovine enzootic abortion
(OEA), which manifests in late pregnancy. Development of a safe and effective
vaccine deployed alongside existing molecular diagnostic tests remains a
long-term ambition. This approach is dependent on improving our knowledge
of disease pathogenesis that leads to tissue damage (pathogen and immune
cell-mediated) in the sheep placenta. Immune responses that control disease
and those responses that facilitate pregnancy are not always compatible or
completely understood. Interferon-gamma (IFN-É£), the signature cytokine of
T-helper (Th)-1 cells, is known to control C. abortus growth. Little is known
about other cytokines co-expressed during OEA that might contribute to
control or disease progression. Incidentally, knowledge of the existence of
other cluster of differentiation (CD)4+ve T cells that produce interleukin-(IL)-4,
IL-10 or IL-17A in sheep are limited or non-existent. These capability gaps
need to be addressed first, to enable measurement of the quality of immune
responses during pregnancy or OEA.
This thesis addressed the hypothesis:
Systemic immune responses of sheep uniquely correlate with pregnancy
outcome following OEA.
Three major research aims were undertaken:
1. To expand the range of assays to characterise CD4+ve T cell immune
responses in sheep.
2. To develop and apply tools to investigate local immune regulation in the
ovine placenta.
3. To investigate immunological correlates of protection against OEA.
Specific immunological assays developed in this project enabled single cell
identification, multi-parameter cytokine assessment and quantification of
specific immunomodulatory molecule transcripts. Studies revealed that IFN-É£
and IL-10 were initiated upon antigen or mitogen stimulation and their kinetics
are as reported for other mammals. Presumptive T-regulatory cells were
identified in peripheral blood mononuclear cells (PBMC). IFN-É£ and
IL-17A-expressing cells include Th-1 and Th-17 cells which are differentially
represented in mitogen-activated PBMC.
Analysis of placental immunity involved collection of placental tissues and
associated lymph nodes at full term of pregnancy. Selective predominance of
classical major histocompatibility complex Class I transcripts were identified
but no indoleamine-2, 3 dioxygenase-1 transcripts within the placental tissues
were found and no natural killer cell staining observed. Collectively, this
expression pattern of ‘immunological parameters’ are unique to date to
placental mammals.
Refined and new assays were fundamental to the experimental design to
investigate immune responses to OEA. New patterns of Chlamydia-specific
responses were identified. Selective elevation of IFN-É£ and IL-10 during the
latent stage of disease prior to pregnancy was observed. These cytokines
remained elevated during and after active phases of OEA. Measurement of
targeted immunological parameters failed to identify unique responses
correlated with protection and do therefore not support the PhD hypothesis.
This work has significantly extended the knowledge of placental immunity and
cellular immunity during OEA utilizing species-validated immunological
assays. Several new areas of investigation have been identified. Concurrent
progress in antigen discovery, transcriptomic analysis and tissue organoid
cultures have now provided an environment to accelerate innovative research
for reproductive disease vaccinology. Defined protective immune signatures
will inform on the design of new safe vaccines to OEA, by refinement of
protective antigen selection and mechanisms of vaccine delivery. Placental
tissue-associated organoids may facilitate antigen discovery for other sheep
reproductive pathogens. Together, these proposed areas of further
investigation may enable development of novel multi-pathogen vaccines to
prevent reproductive diseases of small ruminants
The extent of placental pathology is negatively correlated to birth weight in ewes infected with the wild-type strain of Chlamydia abortus
The placenta is the organ that allows the exchange of oxygen and nutrients between maternal and foetal blood, supplying the requirements of the growing foetus. Consequently, any factor that alters placental integrity may affect foetal nutrition, viability and lamb birth weight. Reproductive diseases, such as ovine enzootic abortion (OEA), impact on foetal viability due to the reduction in the functional area for maternofoetal exchange. This study aimed to consider the impact of pathological features of OEA placental lesions on lamb birth weight and indirectly on foetal viability. To investigate the relationship between birth weight and various OEA-related parameters, data from 562 lambs/foetuses from animals experimentally challenged with Chlamydia abortus strain S26/3 and from uninfected animals were analysed. The parameters investigated included the number of foetuses/lambs delivered (single/multiple), foetus/lamb sex, length of gestation, the proportion of placentas affected by lesions (percentage of gross placental pathology), foetal viability (live/aborted) and the number of C. abortus organisms shed in post-parturition vaginal excretions. The results suggest that the length of gestation and the proportion of placentas affected by lesions are the main contributors to birth weight variability, whereas the other factors, including foetal viability (live or aborted outcomes), were found to be less relevant co-variables. The study determined the strongest positive and negative correlations between birth weight were with the length of gestation and the extent of placental pathology, respectively. These results may indicate that economic losses associated with OEA infections result not only from aborted foetuses but also from the surviving lambs that are born weaker and consequently are more susceptible to diseases.EEA MercedesFil: Caspe, Sergio Gaston. Moredun Research Institute; Reino UnidoFil: Caspe, Sergio Gaston. Instituto Nacional de TecnologÃa Agropecuaria (INTA). Estación Experimental Agropecuaria Mercedes; ArgentinaFil: Caspe, Sergio Gaston. University of Edinburgh. Royal (Dick) School of Veterinary Studies; Reino UnidoFil: Palarea-Albaladejo, Javier. Biomathematics & Statistics Scotland; Reino UnidoFil: Palarea-Albaladejo, Javier. University of Girona. Deparment of Computer Sciences, Applied Mathematics and Statistics; EspañaFil: Livingstone, Morag. Moredun Research Institute; Reino UnidoFil: Wattegedera, Sean Ranjan. Moredun Research Institute; Reino UnidoFil: Milne, Elspeth. University of Edinburgh. Royal (Dick) School of Veterinary Studies; Reino UnidoFil: Sargison, Neil Donald. University of Edinburgh. Royal (Dick) School of Veterinary Studies; Reino UnidoFil: Longbottom, David. Moredun Research Institute; Reino Unid
Distribution and severity of placental lesions caused by the Chlamydia abortus 1B vaccine strain in vaccinated ewes
Chlamydia abortus infects livestock species worldwide and is the cause of enzootic abortion of ewes (EAE). In Europe, control of the disease is achieved using a live vaccine based on C. abortus 1B strain. Although the vaccine has been useful for controlling disease outbreaks, abortion events due to the vaccine have been reported. Recently, placental pathology resulting from a vaccine type strain (vt) infection has been reported and shown to be similar to that resulting from a natural wild-type (wt) infection. The aim of this study was to extend these observations by comparing the distribution and severity of the lesions, the composition of the predominating cell infiltrate, the amount of bacteria present and the role of the blood supply in infection. A novel system for grading the histological and pathological features present was developed and the resulting multi-parameter data were statistically transformed for exploration and visualisation through a tailored principal component analysis (PCA) to evaluate the difference between them. The analysis provided no evidence of meaningful differences between vt and wt strains in terms of the measured pathological parameters. The study also contributes a novel methodology for analysing the progression of infection in the placenta for other abortifacient pathogens.EEA MercedesFil: Caspe, Sergio Gaston. Instituto Nacional de TecnologÃa Agropecuaria (INTA). Estación Experimental Agropecuaria Mercedes; ArgentinaFil: Caspe, Sergio Gaston. Moredun Research Institute; Reino UnidoFil: Caspe, Sergio Gaston. University of Edinburgh. Royal (Dick) School of Veterinary Studies; Reino UnidoFil: Palarea-Albaladejo, Javier. Biomathematics & Statistics Scotland; Reino UnidoFil: Underwood, Clare. Moredun Research Institute; Reino UnidoFil: Livingstone, Morag. Moredun Research Institute; Reino UnidoFil: Wattegedera, Sean Ranjan. Moredun Research Institute; Reino UnidoFil: Milne, Elspeth. University of Edinburgh. Royal (Dick) School of Veterinary Studies; Reino UnidoFil: Sargison, Neil Donald. University of Edinburgh. Royal (Dick) School of Veterinary Studies; Reino UnidoFil: Chianini, Francesca. Moredun Research Institute; Reino UnidoFil: Longbottom, David. Moredun Research Institute; Reino Unid
Defining immune correlates during latent and active chlamydial infection in sheep
Ovine enzootic abortion (OEA) caused by the obligate intracellular bacterial pathogen Chlamydia abortus (C. abortus), is an endemic disease in most sheep-rearing countries worldwide. Following infection, C. abortus establishes a complex host–pathogen interaction with a latent phase in non-pregnant sheep followed by an active disease phase in the placenta during pregnancy leading to OEA. Improved knowledge of the host–pathogen interactions at these different phases of disease will accelerate the development of new diagnostic tests and vaccines to control OEA. Current evidence indicates that cellular immunity is essential for controlling C. abortus infection. We have previously described a model of mucosal (intranasal) infection of non-pregnant sheep with C. abortus that replicates the latent and active phases of OEA. We have investigated antigen-specific recall responses of peripheral blood mononuclear cells (PBMC) in sheep infected with C. abortus via the intranasal route to determine how these change during the latent and active phases of disease. By analysing cytokines associated with the major CD4+ve Thelper (Th) cell subsets (Interferon-gamma (IFN-γ)/Th1; Interleukin (IL)-4/Th2; IL-17A/Th17; IL-10/Tregulatory), we show that there is selective activation of PBMC producing IFN-γ and/or IL-10 during the latent phase following infection. These cytokines are also elevated during the active disease phase and while they are produced by sheep that are protected from OEA, they are also produced by sheep that abort, highlighting the difficulties in finding specific cellular immunological correlates of protection for complex intracellular pathogens
Efficacy of two Chlamydia abortus subcellular vaccines in a pregnant ewe challenge model for ovine enzootic abortion
Chlamydia abortus, the aetiological agent of enzootic abortion of ewes, is a major cause of reproductive loss in small ruminants worldwide, accounting for significant economic losses to the farming industry. Disease can be managed through the use of commercial inactivated or live whole organism-based vaccines, although both have limitations particularly in terms of efficacy, safety and disease-associated outbreaks. Here we report a comparison of two experimental vaccines (chlamydial outer membrane complex (COMC) and octyl glucoside (OG)-COMC) based on detergent extracted outer membrane preparations of C. abortus and delivered as prime-boost immunisations, with the commercial live vaccine Cevac® Chlamydia in a pregnant sheep challenge model. No abortions occurred in either experimental vaccine group, while a single abortion occurred in the commercial vaccine group. Bacterial shedding, as a measure of potential risk of transmission of infection to naïve animals, was lowest in the COMC vaccinated group, with reductions of 87.5%, 86.4% and 74% observed for the COMC, OG-COMC and live commercial vaccine groups, respectively, compared to the unvaccinated challenge control group. The results show that the COMC vaccine performed the best and is a safer efficacious alternative to the commercial vaccines. However, to improve commercial viability, future studies should optimise the antigen dose and number of inoculations required
The Immune Response in the Uteri and Placentae of <i>Chlamydia abortus</i>-Infected Ewes and Its Association with Pregnancy Outcomes
The enzootic abortion of ewes, caused by the bacterium Chlamydia abortus (C. abortus), is one of the main causes of abortion in sheep. There are multiple contributory factors, including chlamydial growth, host immune response, and hormonal balance, that result in different pregnancy outcomes, such as abortion, the birth of weak lambs that may die, or healthy lambs. This study aimed to determine the relationship between phenotypical patterns of immune cell infiltration and different pregnancy outcomes in twin-bearing sheep (both lambs born dead; one alive and one dead; both alive) when experimentally infected with C. abortus. Both the sheep uteri and placentae were collected after parturition. All samples were analysed for specific immune cell features, including cell surface antigens and the T-regulatory (Treg) cell-associated transcription factor and cytokines, by immunohistochemistry and in situ hybridisation. Some of these immunological antigens were evaluated in ovine reproductive tissues for the first time. Differential patterns of T helper/Treg cells revealed significant group effects in the placentae. It suggests the potential role that the balance of lymphocyte subsets may play in affecting different pregnancy outcomes in C. abortus-infected sheep. The present study provides novel detailed information about the immune responses observed at the maternofoetal interface in sheep at the time of pre-term abortion or lambing