Histological differences in the placenta of three mares treated for ascending bacterial placentitis compared to physiological pregnancies.

Overview

• This study examined the structural differences in the placentas of mares treated for ascending bacterial placentitis compared to healthy pregnancies.
• The researchers focused beyond inflammation to explore cell proliferation, apoptosis, blood vessel formation, and other histological changes in placental tissue collected near term.

Background

• Ascending bacterial placentitis is a common cause of late pregnancy loss in mares, involving bacterial infection that ascends from the cervix to infect the placental tissues.
• Previous studies mainly focused on inflammatory changes in placentitis; this research aimed to assess broader histological differences.
• The goal was to understand how placental tissue changes structurally during infection and treatment compared to normal pregnancies.

Study Design

• Two groups of mares were studied:
  • Physiological pregnancies (PP group, n=8) – mares with normal term pregnancies.
  • Placentitis group (PL group, n=3) – mares treated during late pregnancy for confirmed ascending bacterial placentitis.
• Placental samples were taken from multiple locations on the allantochorion, including the cervical star, base, and tip of both uterine horns.

Methods Used

• Immunostaining techniques targeted:
  • Caspase 3 – a marker for apoptosis (programmed cell death).
  • Ki67 – a marker for cell proliferation.
  • MAC387 – a marker for macrophages, important immune cells involved in inflammation.
• Histochemical stains included:
  • Periodic Acid Schiff (PAS) – to examine blood vessel presence and integrity.
  • Kossa stain – to detect microcalcifications within the placental tissue.

Key Findings

• Increased Cell Proliferation:
  • PL group mares showed significantly increased proliferation (Ki67) of allantochorionic cells at various placental locations compared to PP mares.
  • This indicates active tissue regeneration or compensatory growth during placentitis treatment.
• No Difference in Apoptosis:
  • No significant difference was found in caspase 3 staining between groups, suggesting that programmed cell death levels were not altered by infection or treatment.
• Changes in Vascularization:
  • Healthy pregnancies (PP) had a larger blood vessel area in some placental locations.
  • Placentitis cases (PL) showed a higher number of blood vessels specifically at the base of the pregnant uterine horn, highlighting localized vascular changes possibly supporting increased tissue demands.

Conclusions and Implications

• The observed increased cell proliferation and changes in blood vessel formation suggest that mares experiencing ascending bacterial placentitis may initiate compensatory mechanisms.
• These changes may help to maintain placental function despite tissue damage caused by inflammation.
• Understanding these histological adaptations could inform more effective treatments or monitoring strategies during placentitis in mares, potentially reducing pregnancy loss.