TLR4 and infection: Although E. coli-inoculation in bovine udder has been reported to cause a massive upregulation of TLR-2 and TLR-4 in mammary secretory tissue [36], we found out that TLR-2 but not TLR-4 was upregulated in teat explants exposed to E. coli, suggesting possible differences in the capacity of udder compartments to respond to infection.