CD40 Ligand and CD40: Expression, Regulation, and Function at the Maternal–Conceptus Interface in Pigs

To successfully establish and maintain pregnancy in pigs, a variety of factors must work together at the maternal–conceptus interface to form an immune environment appropriate for both the mother and the conceptus. Our transcriptomics study has shown that cluster of differentiation ligand 40 (CD40L) and its receptor CD40, which are known to play important roles in regulating cell- and antibody-mediated immunity, are expressed in the endometrium during early pregnancy. However, the roles of the CD40L and CD40 signaling system are not well understood. Therefore, we determined the expression, regulation, and function of CD40L and CD40 at the maternal–conceptus interface in pigs. The endometrium expressed CD40L and CD40 mRNAs at the greatest levels on Day 15 of pregnancy. The CD40L protein was localized predominantly to luminal epithelial cells on Day 15 of pregnancy, and the CD40 protein was found in luminal epithelial, stromal, and vascular endothelial cells in the endometrium during pregnancy. During early pregnancy, the conceptus expressed CD40 but not CD40L, and chorioallantoic tissues during mid- to late pregnancy expressed both CD40L and CD40. Interferon-γ increased the expression of CD40L and CD40 in endometrial explants. CD40L increased the migration, but not the proliferation, of cultured porcine endometrial endothelial (pENDO) cells in vitro. In addition, CD40L affected the expression of genes related to angiogenesis, cell adhesion, chemokines, and immunity in pENDO cells. These results suggest that the CD40L-CD40 system might play an important role in the establishment of pregnancy in pigs by regulating endometrial endothelial cell function during the implantation period.