Immunological homeostasis at the ovine placenta may reflect the degree of maternal foetal interaction

Abstract

Successful mammalian pregnancies are a result of complex physiological, endocrinological and immunological processes that combine to create an environment where the mother is tolerant to the semi-allogeneic fetus. Our knowledge of the mechanisms that
contribute to maternal tolerance is derived mainly from human and murine studies of haemochorial placentation. However, as this
is the most invasive type of placentation it cannot be assumed that identical mechanisms apply to the less invasive epitheliochorial
placentation found in other species such as ruminants. Here, we examine three features associated with reproductive immune
regulation in a transformed ovine trophoblast cell line and ex-vivo ovine reproductive tissues collected at term, namely: major
histocompatibility complex (MHC) expression, Indoleamine 2, 3 dioxygenase-1 (IDO-1) expression and Natural Killer (NK) cell
infiltration. High levels of MHC class I protein expression were detected at the surface of the trophoblast cell line using a pan-MHC
class I specific monoclonal antibody. The majority of MHC class I transcripts isolated from the cell line clustered with classical MHC
alleles. Transcriptional analysis of placental tissues identified only classical MHC class I transcripts. We found no evidence of
constitutive transcription of IDO-1 in either the trophoblast cell line or placental tissues. Ex-vivo tissues collected from the
materno-fetal interface were negative for cells expressing NKp46/NCR1. Collectively, these observations suggest that the relatively non-invasive synepitheliochorial placentation found in sheep has a more limited requirement for local immunoregulation compared to the more invasive haemochorial placentation of primates and rodents.