Toll-like receptor 4 (TLR4) plays a significant role in modulation of immunological tolerance in reproductive tract of human female. To better understand the functions of TLR4 in establishing and maintaining the pregnancy in pigs, this study was performed to investigate the cellular expression and distribution patterns of TLR4 in the uterus of pregnant Yorkshire pigs. For this purpose, the uterine tissues from pregnant gilts were obtained on days 15, 26, 50 and 95 of gestation. The distribution of TLR4 in the uterus was analyzed by immunohistochemical technique, using an antibody against TLR4. TLR4 was found in uterine luminal epithelium, uterine glands, trophoblasts and placental blood vessels; TLR4 expression in the trophoblast cells and uterine luminal epithelium, on days 15 and 26 of gestation was higher than that on days 50 and 95 of gestation, and there was nearly same expression between days 50 and 95 of gestation. In uterine glands, the expression of TLR4 protein was nearly equal at all stages of gestation. These results indicated that TLR4 is expressed in different histological layers of the uterus during the pregnancy and it changes with the advancement in gestational stages. These results provided novel information about cellular distribution and the functions of TLR4 in modulating immune tolerance in pig uterus during pregnancy.

Key words: Pig, Pregnancy, Toll-like receptor 4, Uterus