Expression of Toll-like receptors 2, 4 and 6 in different cell populations of the equine endometrium

Subfertility in mares is mainly caused by endometrial diseases. Alterations of Toll-like receptors (TLRs) are associated with endometrial disorders in women. This study investigated TLRs 2, 4 and 6 in the equine endometrium. Endometria of 21 mares were examined by histology, PCR and immunohistochemistry. Tissues from 2 mares were considered normal. The remaining showed endometritis, endometrosis and/or angiosclerosis. TLRs 2, 4 and 6 were expressed as transcripts and proteins in all endometria. Immunohistochemistry detected TLRs 2, 4 and 6 in mast cells, luminal and glandular epithelial cells, stromal cells, endothelia, vascular smooth muscle and/or inflammatory cells. Between examined endometria numbers of immunopositive epithelial cells varied considerably; TLRs were located in their cytoplasm and/or the nucleus. All other cell types displayed a cytoplasmic staining. Results indicate a complex and cell-type-specific modulation of TLRs 2, 4 and 6 in the equine endometrium. The lack of a detectable association between a particular disease and a distinct cellular expression may be explained by the often combined presence of several factors with a possible influence on TLRs. This study expands the basic knowledge on equine endometrial immunity and will assist to uncover if immunological alterations contribute to uterine diseases of mares.