The antibacterial psoriasin is induced by E. coli infection in the bovine udder

Human psoriasin (S100A7) has been described as a member of the family of S100 calcium-binding proteins and is over-expressed in patients suffering from psoriasis. The bovine homolog was first identified as a cow-derived respiratory allergen. Human psoriasin as well as its bovine homolog exhibit antibacterial activity especially against Escherichia coli. During E. coli mastitis, the host defence status is a cardinal factor influencing systemic disease severity, and E. coli mastitis is a common problem in dairy cattle. We therefore examined by immunoblotting and immunohistochemistry whether and in which location the bovine protein is expressed in the mammary gland and whether this expression is inducible by E. coli infection. Additionally, milk samples from the cows were investigated. To obtain an antiserum, rabbits were immunised with recombinant bovine psoriasin. Six German Holstein cows in their first lactation were used; four of them were intramammarily infected with an E. coli strain isolated from udder secretions of cows with clinical mastitis, two cows served as healthy control animals. After 24 h, cows were slaughtered and samples were collected from three different locations of the quarters. Psoriasin expression was limited to the teat cistern of the E. coli-infected cows, but was absent in the teat cistern of the non-infected cows and in the parenchyma of both groups, whereas the expression on udder skin was demonstrated in both infected and non-infected cows. Psoriasin thus appears to be a part of the local host defence mechanisms in the udder and seems to be inducible by infection with E. coli.