- Title
- Human endogenous retroviruses and immune tolerance in pregnancy
- Creator
- Schjenken, John Even
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2011
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- The human placenta expresses endogenous retroviral envelope proteins which have been postulated to play an important role in the physiology of pregnancy. Of these, syncytin-1 and syncytin-2 are highly expressed in the syncytiotrophoblast and cytotrophoblast respectively and are thought to be key factors in the regulation of syncytialisation due to their fusiogenic properties. In addition to their role in cell fusion, it has also been speculated that syncytin-1 and syncytin-2 may have a role in maternal immune tolerance due to the presence of the highly conserved immunosuppressive domain (ISD) within its sequence. However, no studies are yet to confirm this putative role. Another factor which has been speculated to have a role in maternal immune tolerance is Corticotropin Releasing Hormone (CRH) which has been shown to promote implantation and the maintenance of early pregnancy via the regulation of FasL. Interestingly, both syncytin-1 and FasL have been identified in immunosuppressive placental exosomes. Since CRH stimulates cyclic AMP (cAMP) production and syncytin-1, syncytin-2 and FasL are all stimulated by the cAMP second messenger pathway, it was hypothesised that syncytin-1 and syncytin-2 may be regulated by CRH. Further, it was hypothesised that syncytin-1 may contribute to the modulation of the maternal immune environment during pregnancy. To examine the regulation of syncytin-1 and syncytin-2 by CRH, a combined nucleic acid and protein extraction procedure was developed using column based nucleic acid extraction kits. Using 2D buffer, proteins extracted using this method were shown to have a comparable protein profile to conventionally extracted proteins. This method was then used to examine RNA and protein levels in CRH treated BeWo cells. Following CRH treatment of BeWo cells, a significant upregulation of syncytin-1, syncytin-2 and FasL mRNA was observed. CRH also increased the production of the syncytin-1 precursor in an exosomal fraction. To examine the immunosuppressive properties of syncytin-1, the recombinant ectodomains of human and mouse syncytins were produced and purified using a combination of affinity chromatography and gel filtration. The immunosuppressive properties of the syncytin-1 recombinant ectodomain were then tested using a whole blood culture model stimulated with LPS or PHA. Syncytin-1 recombinant ectodomain at a concentration of 1µM inhibited the production of TNF-α by 50% and CXCL10 by 65% in whole blood cultures following maximal stimulation with LPS. Syncytin-1 recombinant ectodomain also inhibited the production of IFN-γ by 30% in PHA stimulated PBMC. These studies demonstrate for the first time that syncytin-1 has immunosuppressive properties. Further, these studies show that CRH has a role in the stimulation of syncytin-1 and its subsequent sorting into exosomes. Circulating placental exosomes containing syncytin-1 and other immunosuppressive factors including FasL may interact with maternal immune cells to prevent an immune response against the fetal-placental unit. This is a novel mechanism that may contribute to our understanding of how a genetically different fetus can be tolerated by the mother during pregnancy.
- Subject
- endogenous retroviruses; pregnancy; syncytialisation regulation; immune tolerance; immunosuppression
- Identifier
- http://hdl.handle.net/1959.13/923742
- Identifier
- uon:9806
- Rights
- Copyright 2011 John Even Schjenken
- Language
- eng
- Full Text
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| View Details Download | ATTACHMENT02 | Thesis | 2 MB | Adobe Acrobat PDF | View Details Download |