TLR4 and escherichia coli infection: In bovine primary mammary epithelial cells (PMECs), E. coli infection induces the expression of Toll-like receptor 2 (TLR2) and Toll-like receptor 4 (TLR4), and cytokines Tumor Necrosis Factor-α, Interleukin-1α, Interleukin-6 and Interleukin-8, and activation of the NFκB pathway; on the other hand, while S. aureus infection induces TLR2 expression, other molecular responses are delayed if present at all [8–11].