In bovine placentomes, the inflammatory response is considered important for the detachment of the fetal membrane from the caruncle after parturition. Glucocorticoids, a trigger of the onset of parturition, facilitate functional maturation of placentomes via prostaglandin (PG) and estrogen production in cattle. This study investigated how exogeneous glucocorticoids, which exert immunosuppressive effects, affect placental inflammation at parturition. Placentomes were collected immediately after spontaneous or induced parturition. Parturition was conventionally induced using PGF2α or dexamethasone or with a combination of triamcinolone acetonide and high-dose betamethasone (TABET treatment). Polymerase chain reaction (PCR) array analysis indicated that 9/13 C-C motif chemokine ligands (CCLs) were upregulated > two-fold in spontaneous parturition, with CCL2 and CCL8 being highly expressed. The expressions of CCL2, CCL8, C-C motif chemokine receptor 1 (CCR1), and CCR5 in caruncles were significantly higher in spontaneous parturition than in induced parturition. Although the clinical dose of dexamethasone did not influence the expression of these CCLs and CCRs, TABET treatment increased CCR1 expression. CCL8, CCR1, CCR2, and CCR5 were localized in the caruncular epithelial cells. CCR2 was also localized in the epithelial cells of the cotyledonary villi. This study is the first report to reveal the disruption in CCL and CCR expression in bovine placentomes at induced parturition. Enhanced glucocorticoid exposure for the induction of parturition may upregulate CCR1 expression in placentomes, but the treatment does not adequately promote CCL expression. Additionally, immunohistochemistry suggested that the CCL-CCR system is involved in the functional regulation of maternal and fetal epithelial cells in placentomes at parturition.
Keywords: Cattle; Chemokine; Parturition; Placenta; Retained fetal membrane.