Characterisation of lymphocyte subsets in the equine oviduct

Reasons for performing study: The equine oviduct is the site of fertilisation and location of embryonic development during the first 5 or 6 days. It therefore has an important influence on mare fertility. Although histopathological changes have been described previously, there is limited information regarding lymphocyte subtypes present in the mucosa of the normal equine oviduct. Objectives: To characterise the distribution of CD3⁺, CD4⁺, CD8⁺ and B lymphocytes in the equine oviduct from inseminated mares during oestrus and dioestrus, and from noninseminated mares during the immediate post ovulatory period. Methods: Oviductal tissues were collected from noninseminated mares at oestrus (>30 mm follicle, n = 4), at Day 1 post ovulation (n = 3) and at dioestrus (Day 7 post ovulation; n = 4). Oviducts were also collected fro m inseminated mares at Days 1, 2, and 3 post ovulation (n = 4 for each period). Cross-sections of tissues from the ampullaristhmic junction from each oviduct were snap frozen and cryostat sections stained by the immunoperoxidase technique with monoclonal antibodies directed against equine lymphocyte surface markers for B cells as well as CD3⁺, CD4⁺ and CD8⁺ cells. Results: In all oviductal sections examined, B cells were rare whereas T cells were relatively abundant. The predominant cell type found was the CD8⁺ phenotype, with a lesser number of CD4⁺ cells. Among mares, individual variation was large; therefore, although breeding status and stage of oestrous cycle appeared to alter lymphocyte populations, these differences were not significant. Conclusions and potential relevance: A population of CD3 ⁺, CD4⁺ and CD8⁺ cells exists within the mucosal region of the equine oviduct. The density of these cells is similar to that described in the human oviduct. Their function is not currently known, but they may be involved with modulation of the maternal response to the presence of spermatozoa or the early conceptus within the equine oviduct. As our capacity to differentiate these cell types improves, along with the ability to identify the specific cytokines they produce, their functional significance will become more apparent.