Background: The regulation of maternal immunity is critical for the establishment and maintenance of successful pregnancy. Among many cell types regulating the immune system, innate lymphoid cells (ILCs) are known to play an important role in innate immunity. Although some reports show that ILCs are present at the maternalconceptus interface in humans and mice, the expression and function of ILCs in the endometrium have not been studied in pigs. Methods: Thus, we determined the expression, localization, and regulation of ILC markers, CD127 (a common marker for ILCs), BCL11B (a ILC2 marker), and RORC (a ILC3 marker) at the maternal-conceptus interface in pigs. Results: The expression of BCL11B and RORC, but not CD127, in the endometrium changed during pregnancy in a stage-specific manner and the expression of CD127, BCL11B, and RORC was greatest on Day 15 during pregnancy. CD127, BCL11B, and RORC were also expressed in conceptus tissues during early pregnancy and in chorioallantoic tissues during the later stage of pregnancy. BCL11B and RORC proteins were localized to specific cells in endometrial stroma. The expression of CD127 and BCL11B, but not RORC, was increased by the increasing doses of interferon-γ (IFNG) in endometrial explants. Conclusions: These results suggest that ILCs present at the maternal-conceptus interface may play a role in the establishment and maintenance of pregnancy by regulating the innate immunity in pigs.

The cellular communication network factor (CCN) family proteins regulate many biological events such as angiogenesis, tumor growth, placentation, implantation, and embryogenesis. The expression and function of CCN1, CCN2, and CCN3 at the maternal-conceptus interface are established in humans and rodents, but little is known about the role of CCN4 to CCN6 in the reproductive organs in any other species. Several studies in transcriptome analysis in pigs have shown that the expression of CCN4 and CCN6 increases in the endometrium during early pregnancy. However, their expression, regulation, and function in the endometrium throughout the estrous cycle and pregnancy have not been fully understood in pigs. Thus, we determined the expression, localization, and regulation of CCN4 and CCN6 during the estrous cycle and at the maternal-conceptus interface in pigs. We found that the levels of CCN4, but not CCN6, changed during the estrous cycle. The levels of CCN4 were greater during mid- to late pregnancy than in the early stage, and the levels of CCN6 were greatest on Day 15 of pregnancy. CCN4 and CCN6 were detected in conceptus tissues during early pregnancy and in chorioallantoic tissues during the later stage of pregnancy. CCN4 mRNA was mainly localized to epithelial cells, CCN6 mRNAs to epithelial and stromal cells in the endometrium. In endometrial explant cultures, CCN4 expression was increased by progesterone, and CCN6 expression by interferon-γ. These results suggest that CCN4 and CCN6 may play roles in the establishment and maintenance of pregnancy by regulating the endometrial epithelial cell functions in pigs.