Programming of the endometrial immune milieu by interferon gamma during early pregnancy in pigs

Release of interferon-gamma (IFNG), a pro-inflammatory type II interferon, by the early conceptus is critical for pregnancy establishment in the pig. Yet, the cellular and molecular mechanisms underpinning conceptus-derived IFNG actions in maternal peripheral immune cells and at the embryo-maternal interface remain unclear. Here we show that pregnancy status up-regulates expression of IRF1, an IFNG target-gene, in peripheral blood mononuclear cells on day 15 of pregnancy in the pig. In a second study, loss-of-function IFNG (IFNG-/-) embryos were generated by using CRISPR/Cas9 gene editing and somatic cell nuclear transfer. Single-nuclei RNA sequencing of endometrium from gilts carrying wild-type (Control) or IFNG-/- conceptuses on day 15 of pregnancy revealed cell-type-specific signatures at the embryo-maternal interface in response to conceptus IFNG. Changes in the transcriptome of epithelial and IFNG receptor-expressing immune cells were evident between Control and IFNG-/- samples, along with a downregulation of IFNG target-genes involved in chemotaxis and immune cell differentiation in IFNG-/- recipient endometria. A notable reduction in monocytes and macrophages was observed in IFNG-/- samples, confirmed by immunohistochemistry for AIF1. Differential gene expression (DEG) analysis revealed 391 DEGs in monocytes, implicating IFNG in macrophage polarization, with evidence suggesting a shift toward an M2 phenotype. The study concludes that conceptus IFNG plays an important role in monocyte recruitment and macrophage polarization at the embryo-maternal interface for regulation of inflammation upon conceptus attachment. Insufficient numbers or skewed IFNG-activated macrophages within the endometrium may contribute to pregnancy failure in the IFNG-/- pig model.