title: The endogenous retroviral envelope protein syncytin-1 inhibits LPS/PHA-stimulated cytokine responses in human blood and is sorted into placental exosomes.
abstract: OBJECTIVE
  To examine whether syncytin-1 has immune regulatory functions and is carried by human placental exosomes. Further, to examine whether corticotropin-releasing hormone (CRH) can induce the production of syncytin-1.
  
  
  METHODS
  Human placental exosomes were isolated from placental explant, primary trophoblast and BeWo cell cultures. The presence of exosomes was confirmed by transmission electron microscopy and western blotting. Exosomal protein was probed with 3 separate antibodies targeting syncytin-1. Syncytin-1 immunosuppression was tested, using either a syncytin-1 recombinant ectodomain protein or a synthetic peptide with the human syncytin-1 immunosuppressive domain sequence, in an in vitro human blood culture system immune challenged with LPS or PHA. The inhibition of cytokine production by syncytin-1 was determined by ELISA of TNF-α, IFN-γ and CXCL10. BeWo cells were stimulated with CRH or vehicle for 24 h. mRNA and Protein was extracted from the cells for real-time PCR and western blotting analysis while exosomes were extracted from conditioned media for analysis by western blotting.
  
  
  RESULTS
  Protein expression of syncytin-1 was detected in exosomes isolated from placental explants, primary trophoblast and BeWo cell cultures. Syncytin-1 recombinant ectodomain was also shown to inhibit the production of the Th1 cytokines TNF-α and IFN-γ as well as the chemokine, CXCL10 in human blood cells. Finally, this study showed that syncytin-1 can be stimulated by CRH.
  
  
  CONCLUSIONS
  The presence of syncytin-1 in placental exosomes provides a mechanism for syncytin-1 to reach and interact with target cells of the maternal immune system and represents a novel mechanism of endogenous retroviral mediated immunosuppression that may be relevant for maternal immune tolerance.
authors.affiliation: Mothers and Babies Research Centre, The University of Newcastle, Level 3, Endocrine Unit, John Hunter Hospital, New Lambton Heights, 2305 NSW, Australia. jorge.tolosa@newcastle.edu.au
authors.forename: J M
authors.initials: JM
authors.lastname: Tolosa
authors.forename: J E
authors.initials: JE
authors.lastname: Schjenken
authors.forename: V L
authors.initials: VL
authors.lastname: Clifton
authors.forename: A
authors.initials: A
authors.lastname: Vargas
authors.forename: B
authors.initials: B
authors.lastname: Barbeau
authors.forename: P
authors.initials: P
authors.lastname: Lowry
authors.forename: K
authors.initials: K
authors.lastname: Maiti
authors.forename: R
authors.initials: R
authors.lastname: Smith
mesh_terms: D000328:Adult; D001692:Biological Transport; D002460:Cell Line; D002478:Cells, Cultured; D003346:Corticotropin-Releasing Hormone / Q000378:metabolism; D016207:Cytokines / Q000235:genetics / Q000378:metabolism*; D020077:Endogenous Retroviruses / Q000378:metabolism; D055354:Exosomes / Q000276:immunology / Q000378:metabolism* / Q000648:ultrastructure / Q000821:virology; D005260:Female; D005786:Gene Expression Regulation; D015686:Gene Products, env / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007108:Immune Tolerance; D007963:Leukocytes, Mononuclear / Q000276:immunology / Q000378:metabolism*; D008070:Lipopolysaccharides; D010835:Phytohemagglutinins; D010920:Placenta / Q000276:immunology / Q000378:metabolism* / Q000648:ultrastructure / Q000821:virology; D011247:Pregnancy; D011257:Pregnancy Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D046509:Tissue Culture Techniques
chemical_list: D016207:Cytokines; D015686:Gene Products, env; D008070:Lipopolysaccharides; D010835:Phytohemagglutinins; D011257:Pregnancy Proteins; D011994:Recombinant Proteins; C405335:syncytin; D003346:Corticotropin-Releasing Hormone