PreImplantation Factor (PIF) displays developmental-related evolving immune anti-inflammatory response of equine endometrial explants in vitro

AIMS: PIF, secreted only by viable mammalian embryos is essential for achieving maternal immune-tolerance without immune-suppression. In human endometrium PIF coordinates and supports implantation and modulates immunity. Transposed to non-pregnant models, PIF displays immune-control and regenerative features in neuroinflammation and diabetes. The aim was to test the hypothesis that PIF exerts anti-inflammatory properties towards equine endometrium challenged with Escherichia coli-derived lipopolysaccharide (LPS) using an established endometrial explant culture model of uterine inflammation. METHODS: Luteal (n = 4) and anoestrus (n = 8) stage endometrium was collected from slaughtered mares. Explants were cultured in triplicate in serum-free medium alone (control) and with 0-1000nM sPIF (25-100nM = human physiologic dose) and ± LPS (3µg/ml). Media samples were collected at 24 and 72 h and prostaglandin F2α (PGF2α) secreted into cultured medium was used as a marker of inflammation determined by radioimmunoassay. RESULTS: In luteal stage explants spontaneous PGF2α secretion compared to control (1374 ± 113ng/ml) was abrogated by sPIF at concentrations of 50nM (1273 ± 107ng/ml) and 100nM (1029 ± 113ng/ml) after 72 h. Moreover, in luteal-stage explants, LPS (1576 ± 87 ng/ml) stimulated a PGF2α increase compared to control (vs 1374 ± 113 ng/ml) that was abrogated by sPIF at concentrations of 50nM (1349 ± 87 ng/ml) and 100nM (1331 ± 54ng/ml) at 72 h. In anoestrus-stage explants spontaneous PGF2α secretion compared to control (491 ± 57 ng/ml) was abrogated by sPIF at concentrations of 100nM (421 ± 49ng/ml) and 500nM (378 ± 42ng/ml) after 24 h. In anoestrus tissue LPS did not stimulate PGF2α secretion vs control. CONCLUSION AND PRACTICAL SIGNIFICANCE: sPIF treatment exerts anti-inflammatory effects blocking both LPS-induced and spontaneous PGF2α and its effect is modulated by the stage of oestrous cycle. Data advocates sPIF anti-inflammatory role in non-pregnant endometrium which complements PIF’s essential role in supporting embryo implantation.