A research project funded by The Horse Trust has discovered for the first time expression of a protein in horses known to be important in maintaining pregnancy.
The research project was undertaken by Dr Lucy Woolford at the Royal Veterinary College, who is now working as a Lecturer in Veterinary Pathology at the University of Adelaide, Australia.
Infertility and foetal loss are a significant problem within the equine industry, causing distress to both the owners and the mares. In around 20 percent of cases, the cause of foetal loss is unknown (Smith et al 2003).
The research, funded by The Horse Trust, aimed to understand more about how pregancy is maintained in horses and to learn more about how equine herpevirus may trigger foetal loss.
Maintaining a viable pregnancy is dependent on the ability of the mother’s immune system to 'tolerate' the immunologically 'foreign'
foetus. The ways in which mares tolerate the developing foetus is not fully understood, but in humans, primates and mice a protein called indoleamine 2,3-dioxygenase (IDO) produced by the pregnant uterus has been shown to be important.
The research team looked for the presence of IDO and the expression of genes coding this protein in archive tissues of equine placentas using immunochemistry and PCR. They found that IDO was expressed in the equine placenta between days 40 and 70 of gestation, correlating with early invasive stages of placental development in the mare. This finding suggests that expression of IDO in the equine placenta may help prevent immunological rejection of pregnancy, as it does in other animals.
The researchers also performed preliminary invesgitations into expression of IDO in equine herpesvirus-1 (EHV-1) infected mares. A previous study found infection with equine herpesvirus to be the cause of equine foetal loss in 6.5 percent of cases in the UK (Smith et al 2003). It is also a distressing cause of foetal loss as abortions commonly occur in last month of pregnancy (the gestation period in horses is 11 months).
The researchers found strong expression of IDO in multiple uterine blood vessels of an EHV-1 infected mare that had aborted her foetus. This suggests that expression of IDO may be involved in viral abortion, however further research with a larger sample size is needed to determine the importance of this protein in equine herpesviral abortion.
"We believe this research, which was funded by The Horse Trust, is the first study ever to describe the expression and localisation of IDO in equine tissues," said lead researcher Woolford. "More research is needed to understand the immunology of pregnancy and how IDO might contribute to maintenance of pregnancy in mares. More research is also needed to further understand how equine herpevirus causes foetal loss."