Keratin and S100 calcium-binding proteins are major constituents of the bovine teat canal lining

The bovine teat canal provides the first-line of defence against pathogenic bacteria infecting the mammary gland, yet the protein composition and host-defence functionality of the teat canal lining (TCL) are not well characterised. In this study, we subjected TCL scrapings from six healthy lactating dairy cows to two-dimensional electrophoresis (2-DE) in order to identify proteins that may be involved in immune defence of the mammary gland. Two dominant clusters of proteins were detected in the TCL, and these were identified as members of the keratin and S100 families of proteins. The S100 proteins were localised by immunofluorescence to the teat canal keratinocytes and were particularly predominant in the cornified outermost layer of the teat canal epithelium. Significant between-animal variation in the abundance of the S100 proteins in the TCL was demonstrated by western blot analysis. Four of the six identified S100 proteins have been reported to have antimicrobial activity, suggesting that the TCL acts not just as a physical barrier, but also as a biochemical barrier to invading microorganisms. These findings raise the possibility that the abundance of the S100 proteins in the TCL of individual cows may influence their susceptibility to mastitis. This study provides a basis for future studies aimed at understanding the role of S100 proteins in the host-defence of the bovine mammary gland and the development of novel tools for mastitis management.