Evaluation of the systemic acute phase response and endometrial gene expression of serum amyloid A and pro- and anti-inflammatory cytokines in mares with experimentally induced endometritis

Infectious infertility in the mare is clinically well described, little is however known about the systemic acute phase reaction (APR) and local immunological responses accompanying equine endometritis. The aim of this study was to monitor selected markers of the APR in the systemic circulation and to correlate them to the local innate immune response in the uterus during infectious endometritis. Six adult standard bred mares received an intrauterine infusion of 109 CFU Escherichia coli. Blood samples were obtained before (0 h) and 3, 6, 12, 24, 36, 48, 72, 96 and 120 h post inoculation (pi), and endometrial biopsies were sampled before, and 3, 12, 24, 48 and 72 h pi. The infectious endometritis elicited a systemic APR with significantly increased concentrations of the acute phase proteins (APPs) serum amyloid A (SAA) and fibrinogen. Relative gene expression analyses were performed on extracted RNA from endometrial biopsies using quantitative real-time PCR and specific primers for SAA and pro- and anti-inflammatory cytokines. Expression of SAA was significantly up-regulated at 3 and 12 h pi, and a significant up-regulated expression of IL-1β, TNFα, IL-8 and IL-10 was observed at 3 h pi. Plasma concentration of SAA was significantly correlated to endometrial SAA expression. The results of the present study demonstrate that endometritis gives rise to a systemic APR and an up-regulated endometrial gene expression of SAA and several pro-and anti-inflammatory cytokines. Understanding endometrial expression of acute phase proteins and selected cytokines contributing to uterine immunity in equine endometritis could improve understanding of events leading to infertility in the mare and help identify candidate genes of mediators/markers for diagnostic use.