Elevated levels of cyclophilin A secreted in milk during bovine mastitis

Bovine mastitis is an inflammatory disease that primarily occurs when bacteria invade and proliferate in the mammary gland, although it can also be caused by physical trauma. Mastitis results in a decrease in milk yield and quality, causing huge economic losses. Cyclophilin A (CyPA) is a cytosolic protein known as cyclosporine binding protein. Recent studies have shown that CyPA is secreted from cells and has chemotactic activity, recruiting inflammatory cells and inducing multiple cytokines. In this study, we found that CyPA is detected in milk and is abundantly secreted at the onset of mastitis. A significant correlation was found between SCC and the concentrations of CyPA in milk. To elucidate the relationship between mastitis and CyPA, we gave an intramammary infusion of Staphylococcus aureus to cattle and investigated the attendant CyPA secretion. In S. aureus-infused quarters, we observed an increased expression of CyPA on mammary epithelia and secretion into milk. The temporal profiles of CyPA in milk were synchronous with SCC, and there was a significant correlation between the concentration of CyPA in milk and SCC. These results suggest that CyPA is involved in the migration of immune cells during the onset of mastitis and may be used as a marker for the onset of mastitis.