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Gynaecologic immunologic research aims to answer an important question: How does the immune system manage to protect both mother and unborn child while not harming the semi-allogeneic and thus partially unaccustomed fetus? Several distinct adaptions in both the innate and adaptive immune system take place during pregnancy. Alterations in these processes can cause dramatic consequences like pregnancy loss. Here, molecules with immunomodulatory functions can provide possible treatment options. One molecule with the described features emerged as a candidate: The transmembrane molecule mCD83 as well as its soluble form, sCD83. As mCD83 overexpressing cells and cells from pregnant mice showed similar behaviour regarding interleukin-10 secretion and B-cell (BC) development, a contribution of mCD83 in immunologic pregnancy adaptions is possible. Additionally, the soluble form could be a future therapeutic agent in pregnancy disorders, regarding its already shown benefits in therapy of various autoimmune diseases in animal models.
The aim of this work is to evaluate the expression, release and regulation of CD83 in its membrane bound and soluble forms during normal and disturbed pregnancies in mouse models.
The semi-allogeneic pairing of two inbred stems, C57Bl6/J×BALB/c, results in healthy pregnancy and was used to investigate the expression in different stages of pregnancy. Pairing CBA/J females with DBA/2J males results in resorption of fetal units and represents a poor pregnancy outcome mating (PPOM). This model in comparison with CBA/J×BALB/c pairings (presenting a good pregnancy outcome mating (GPOM)) is a model for immunologic pregnancy disturbance. It was used to detect alterations in mCD83 expression and sCD83 release during disturbed pregnancy.
During normal murine pregnancy, mCD83 expression increased with a peak on day 14 of pregnancy on B- and T-cells, while the amount of mCD83 positive cells was elevated at the end of pregnancy. PPOM mice showed higher mCD83 expression and mCD83 positive cell count on various lymphocyte subtypes in comparison to GPOM, while sCD83 levels were lower in PPOM pregnancies. Splenocytes released sCD83 in cell culture, whereby the main part under unstimulated conditions was produced by BC. Progesterone treatment of splenocytes led to a dose dependent mCD83 upregulation on T-cells and reduced mCD83 expression as well as sCD83 release from BC. Culture of splenocytes with tissue inhibitor of metalloproteinases 1 (TIMP1) resulted in elevated sCD83 release and mCD83 expression on BC. Progesterone reduced TIMP1 expression on BC in vitro.
mCD83 expression and sCD83 release showed various alterations during normal murine pregnancy as well as when comparing PPOM with GPOM. Noticeable are in particular a higher mCD83 expression on splenic BC on day 14 of pregnancy. In BC from PPOM, mCD83 expression is higher than on BC from GPOM, while PPOM mice show a lower sCD83 serum level, hinting a problem in the shedding mechanism during PPOM.
Progesterone regulates mCD83 expression on BC via TIMP1 and a yet unknown proteinase, resulting in degradation of mCD83 with lower mCD83 expression and sCD83 release. Here, the resulting expression level may vary depending on the BC surroundings and cell compartmentation.
The results thereby suggest a CD83 involvement in pregnancy and encourage further research on mCD83 expression at the feto-maternal interface as well as sCD83 in human blood and tissue. Especially the sCD83 alterations are of clinical interest, indicating the molecule as potential therapeutical option for pregnancy disturbances.
Viral diseases are a threat to bacteria and enormous animals alike. Vaccines are available against several viruses. However, for some viruses, like ASFV, we still lack vaccines, while for others, like IAV, they are not as effective as we need them to be. To a large extent, this is because we do not fully understand the mechanisms conferring antiviral immunity. To improve our understanding of antiviral immunity, we used a model species that is in many immunological aspects closer to humans than the widely used laboratory mice, pigs. In this thesis, pigs were investigated as a potential biomedical model species for viral respiratory infections in humans and as a natural host for viral infections. Both approaches provide valuable insights into aspects of porcine immunology that can either be used as the foundation for translational research or for the design of targeted therapeutics and vaccines for pigs.
Insights into fundamental characteristics of the porcine immune system form the basis for translational studies. Paper I pioneered a detailed characterization of porcine iNKT cells. To make pigs and porcine iNKT cells more available for scientific investigations, we established multicolor flow cytometry analysis platforms that allow for a more detailed investigation of these cells than previously possible. We found porcine iNKT cells circulating in peripheral blood to be a rare population among CD3+ lymphocytes that displays a pre-activated effector state and can be divided into at least three functional subsets. Upon antigenic activation, they proliferated rapidly, secreted pro-inflammatory cytokines, and exerted cytotoxicity. Moreover, we provided first evidence for a role of iNKT cells in porcine IAV and ASFV infections, which we investigated in more detail in paper IV. Central characteristics, i.e., phenotype and functional properties, exhibit a high degree of similarity between humans and pigs. Moreover, differences between human and murine iNKT cells are more pronounced than between humans and pigs.
Based on the results obtained in paper II, the established biomedical model could be used for further studies of infectious respiratory diseases. IAV infections pave the way for secondary co-infections with increased morbidity and lethality. These bactoviral co-infections are a threat to both pigs and humans. The shared susceptibility as well as homologies on the physiological and immunological level make pigs exceptionally suitable animal models for studies of these infections. Paper I and II can also be interpreted under translational aspects. Activation of iNKT cells in porcine vaccination studies showed promising results. Based on these and our findings, this might be a suitable approach for humans as well. Along with other studies, our results suggest that pigs might be a well-suited large animal model for research in infectious diseases. This is true especially for respiratory infections, such as seasonal IAV infections, for which pigs are natural hosts and contribute to viral spread and emergence as “mixing vessels”, which can result in pandemic strains like H1N1pdm09. We could show that porcine iNKT cells as well as the antiviral responses of cTC against H1N1pdm09 in pigs are comparable to human cells and processes. The increased implementation of pigs in basic and applied research might enable an improved translation of scientific knowledge to human and veterinary medicine.
In two further studies, papers III and IV, we investigated T-cell responses during a viral infection, ASF, for which pigs are the only natural hosts. Immune responses were similar after highly and moderately virulent ASFV infection in domestic pigs and wild boar, respectively. However, they differed between both species. Antiviral immunity in domestic pigs was predominantly exerted by αβ T cells, CD8α+ and DP αβ T cells, while the response in wild boar was dominated by γδ T cells, mainly CD8α+ effector cells. Since wild boar show a higher disease severity and lethality, even during infection with moderately virulent ASFV “Estonia2014”, a shift to γδ T cells seems to be detrimental. In contrast, domestic pigs survive infections with moderately virulent ASFV “Estonia2014”, which indicates that CD8α+ or DP αβ T cells confer protection at least in infections with non-highly virulent ASFV strains. Interestingly, in paper V we found higher and prolonged inflammation in domestic pigs, correlating with increased T-cell influx. However, histopathological analyses revealed no direct explanation for the differences in disease progression and lethality in domestic pigs and wild boar. These findings require further studies to elucidate the underlying mechanisms.
The lack of basic data about immunological differences between domestic pigs and wild boar hampers attempts to understand immunity against ASFV. We found differences between both suid subspecies already at steady state and even more prominent during ASFV infections in papers III-V. Most apparently, T-cell responses in wild boar were heavily biased towards γδ T cells, while immune responses in domestic pigs were based on αβ T cells. However, information about even basic characteristics, like the composition, phenotypes, and functional qualities of wild boar’s immune system, is missing. Therefore, essential baseline data must be obtained in order to adequately assess changes in future studies.
Analyses like these reveal major advantages of pigs as a biomedical model. On the one hand, similar to conventional model species, researchers can investigate every tissue at any desired time. Tissue from human patients is often scarce or not at all available, so models that can be investigated at specific times after infection are needed. On the other hand, results obtained in pigs are more comparable to humans than data from murine studies. Moreover, pigs are susceptible to similar pathogens as humans and experimental infections can be investigated without the need for major genetic manipulations. However, there are also limitations of the porcine model system. Analysis tools are not as advanced as they are for mice, especially in terms of availability of mAbs or genetically modified organisms. Still, given the major advantages that become more and more obvious, efforts should be made to make pigs more applicable for basic and translational research. In addition, findings derived from pigs can be used for the species itself. Pigs are a major livestock species and new treatments, or vaccines could also be used for them. Therefore, this research could eventually also improve animal welfare.
In summary, the presented thesis significantly enhanced our knowledge of porcine immune processes for cTC in general and iNKT cells in particular. Results were obtained both at steady state and in the context of IAV and ASFV infections, and thus, made pigs more available as a model for future research. The use of multicolor flow cytometry provided a broad overview of the ongoing immune reactions and enables further, more wide-ranging studies that can also address open questions in even more complex infection scenarios.