Characterisation of immune cells within the equine endometrium – a true challenge!

Abstract

In mares, endometrial diseases including endometritis are the main cause of pregnancy failure. A frequent finding in equine endometrial biopsies is non-suppurative endometritis. An immune mediated pathogenesis of this disease appears likely. A more detailed characterization of the involved lymphocyte and macrophage populations can be performed on zinc-salt fixed equine endometrial biopsies. The zinc-salt fixation is a cost-effective ready to use solution and permits the routine histologic diagnosis of endometrial diseases in mares. By using this method, the following immunohistochemical features of non-suppurative endometritis were revealed: It is a predominantly CD3+ T cell mediated disease with the frequent contribution of small numbers of CD20+ B cells and CD172a+ macrophages. Marked individual differences in the contribution of CD4+ helper T cells and CD8+ cytotoxic T cells exist, and the total number of CD3+ T cells often exceeded the sum of the CD4+ and CD8+ cells indicating the presence of CD4-/CD8-double negative T cells. Differences in the relative numbers of CD3+, CD4+ and CD8+ T cells are also detected in endometria without inflammation. These results indicate that several forms of non-suppurative endometritis may exist and that individual factors likely contribute to differences in the immune cell composition of this disease.