The proteome of fetal fluids in mares with experimentally-induced placentitis

Introduction: Placental inflammation (placentitis) is one of the leading causes of late-term abortion in mares. Although prognosis is good assuming early diagnosis and treatment, diagnostics are limited. Methods: To better characterize the disease and identify potential biomarkers, we analyzed the proteome of fetal fluids (amniotic and allantoic) in both control mares (n = 5) and mares with experimentally-induced placentitis (n = 5) using LTQ-Orbitrap mass-spectrometry. Placentitis was induced via trans-cervical inoculation of Streptococcus equi ssp. zooepidemicus. Results: In total, 130 proteins were identified in either amniotic fluid, allantoic fluid, or both, with amniotic proteins being more prevalent and better conserved across samples. A total of 18 proteins were up-regulated in amniotic fluid during placentitis, including haptoglobin, plasminogen isoform X2 and plasminogen-like isoform X1 which were found exclusively in samples from mares with placentitis. Five allantoic proteins were up-regulated, of which four were also found to be up-regulated in amniotic fluid, including alpha-1-antiproteinase and transferrin family members. A total of 19 proteins were down-regulated in amniotic fluid, with none decreasing significantly in allantoic fluid. Discussion: We have performed the first proteomic analysis of amniotic and allantoic fluid during placental infection in any domestic livestock species. We identified a number of proteins with significantly altered expression, primarily those related to immune function. These findings provide information on the physiology of placentitis as well as identify potential biomarkers for future diagnostic work.