Expression profile of proinflammatory mediators in the placenta of mares during physiological detachment and retention of fetal membranes.

Physiological parturition is characterized by sterile, inflammatory-like processes. During parturition, the placenta expresses various proinflammatory mediators, such as chemokines and IL-17. Nevertheless, inflammatory processes present in the parturient mare are poorly characterized. The aim of this study was to investigate the expression of selected chemokines and IL-17 in the allantochorion and the endometrium of mares that retained fetal membranes (RFM) and expelled them physiologically. We hypothesized that the expression of these mediators may be altered in the placenta of mares with RFM and result in RFM occurrence. Differences in mRNA expression in the placenta of investigated groups of mares were detected for CCL2, CCL3, CCL4, CCL8, CXCL1, CXCL8, CXCL10, CX3CL1 and IL-17. There were no differences in mRNA expression of CCL5 and CXCL6. Gene ontology network analysis showed enrichment in genes related to leukocyte migration, cell chemotaxis and response to chemokine in tissues of RFM mares. Analysis of association network suggested denotations between CXCL6, CXCL8, CXCL1, CCL5, CCL4, CX3CL1 and CXCL10. Moreover, possible inhibition of CXCL10 by IL-17A and prostaglandin peroxide synthase 2 (PTGS2) by CXCL1 was detected. Our results suggest that, based on differences in chemokines and IL-17 expression, recruited subsets of leukocytes might differ between the analyzed groups of mares, which in turn may impair the separation of fetal membranes in the group of RFM mares. In addition, the results of the expression analysis suggest that macrophages might be one of the most abundant cells infiltrating the equine placenta during the expulsion of fetal membranes. Furthermore, we suspect that the synthesis of PTGS2 might be inhibited in mares with RFM.