Plasminogen activators in bovine milk during mastitis, an inflammatory disease

Abstract

We have investigated the content of plasminogen activators in bovine milk during mastitic inflammation induced by Staphylococcus aureus. Using sodium dodecyl sulfate-polyacrylamide gel electrophoresis in combination with fibrin agarose zymography and a coupled peptidyl anilide plasminogen activation assay of samples of whey prepared by acidification, we found that the level of tisue-type plasminogen activator (t-PA) in milk was increased immediately after infection and remained elevated during an experimental period of 42 days. The maximal increase was 10 to 20-fold. By zymography, we also demonstrated a strong increase in urokinase-type plasminogen activator (u-PA) associated with the bovine cells in the milk. By ligand blotting, we demonstrated an increase in the level of the urokinase-receptor (u-PAR) on the milk cells during inflammation. Plasma kallikrein was also detected as a plasminogen dependent proteolytic activity by zymography of whey samples. When analyzed in the presence of the t-PA in the milk, the plasma kallikrein lysis zone was strongly increased in mastitic whey, but when analyzed after separation from t-PA, its level was unaffected by mastitis; this could be ascribed to a t-PA dependent stimulation of plasma prekallikrein. These results suggest an important role for plasminogen activators in the inflammatory response during bovine mastitis. Using an enzyme-linked immunosorbent assay we measured the plasminogen/plasmin level during the inflammation, but found a less than 2-fold increase during the experimental period.