Expression of proinflammatory cytokines IL-1β, IL-6 and TNFα in the retained placenta of mares

Retained fetal membranes (RFM) is a prevalent postpartum disease in mares. During parturition, various proinflammatory cytokines are released in the placenta, which further facilitates uterine contractions, expulsion of the fetus and fetal membranes. We hypothesized that an altered inflammatory response in mares results in retained fetal membranes. Samples of the endometrium and the allantochorion were collected from 15 mares with RFM and from 29 control mares within 2 h of foal delivery. Next, the mRNA expression of IL-1β, IL-6 and TNFα proteins was analyzed by Real Time PCR and Western blot. These cytokines were also localized by immunocytochemistry. In mares with RFM, the mRNA expression of IL-1β in the endometrium (p < 0.05) and IL-6 in the allantochorion (p < 0.0001) was higher than in mares that expelled fetal membranes physiologically. Higher expression of IL-6 in the allantochorion was confirmed by Western blot. In contrast, no changes in TNFα mRNA and protein expression were observed between the 2 groups of mares. Moreover, TNFα mRNA was barely detectable. The presence of all studied cytokine proteins in the allantochorion was confirmed by immunocytochemistry. The results suggest that the outbreak of inflammation is involved in the mechanism of placenta release in mares. Increased expression of IL-6 in the allantochorion and IL-1β in the endometrium could reflect a local immune response which leads to the detachment of fetal membranes. The low expression of TNFα mRNA might suggest that this cytokine is not involved in the expulsion of fetal membranes. Further work is needed to determine the exact role and timing of inflammatory activation in fetal membranes during equine parturition.