Abstract：Toll-like receptor 4 (TLR4) is a typeⅠtransmembrane protein and widely expressed in mammalian cell surface, which plays an important role in anti-infection immunity. To explore the expression of Toll-like receptor 4 (TLR4) in the Small Tail Han sheep (Ovis aries) mastitis tissue which caused by Escherichia coli. In the study, E.coli (O113 type) were used to infect Small Tail Han sheep breast and built the mastitis pathological model. The relative expression of TLR4 gene in the normal breast tissue and the breast tissue was infected with E.coli were detected by the methods of qRT-PCR. The expression and distribution of TLR4 protein in the normal breast tissue and the breast tissue infected with E.coli were examined by Western-blot and immunehistochemical SP method. The results showed that the TLR4 expressed in both normal breast tissue and the breast tissue infected with E.coli, but the TLR4 mRNA and protein expressed were highest in 48 h post-infection, and the expression of TLR4 mRNA and protein in 96 h post-infection had significantly lower than 48 h (P＜0.05), and the relative levels of TLR4 was lowest in normal control group (P＜0.05). The results of immunohistochemistry demonstrated that TLR4 expressed in the breast epithelium in both normal breast tissue and the breast tissue infected with E.coli. Compared with the control group, the positive expression was significantly enhanced after infected (P＜0.05). The results of this study showed that the expression of TLR4 was obviously increased after infected with E.coli in breast tissue of Small Tail Han sheep, which will establish the foundation the mechanism of TLR4 in sheep mastitis morbidity process during further study.
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