TLR4 and mastitis: Thus, in the mastitis-free and -affected ewes, the regulation mechanisms of IFN-γ, IL-4, TNF-α, MYD88, CCL5, TLR4, TLR9, LTF, PRLR, CAT, GPX1, Keap1, OXSR1, ATOX1, GST, and Nrf2 are well known.