PLASMINOGEN ACTIVATORS IN BOVINE-MILK DURING MASTITIS, AN INFLAMMATORY DISEASE

We have investigated the content of plasminogen activators in bovine m ilk during mastitic inflammation induced by Staphylococcus aureus. Usi ng sodium dodecyl sulfate-polyacrylamide gel electrophoresis in combin ation with fibrin agarose zymography and a coupled peptidyl anilide pl asminogen activation assay of samples of whey prepared by acidificatio n, we found that the level of tisue-type plasminogen activator (t-PA) in milk was increased immediately after infection and remained elevate d during an experimental period of 42 days. The maximal increase was 1 0 to 20-fold. By zymography, we also demonstrated a strong increase in urokinase-type plasminogen activator (u-PA) associated with the bovin e cells in the milk. By ligand blotting, we demonstrated an increase i n the level of the urokinase-receptor (u-PAR) on the milk cells during inflammation. Plasma kallikrein was also detected as a plasminogen de pendent proteolytic activity by zymography of whey samples. When analy zed in the presence of the t-PA in the milk, the plasma kallikrein lys is zone was strongly increased in mastitic whey, but when analyzed aft er separation from t-PA, its level was unaffected by mastitis; this co uld be ascribed to a t-PA dependent stimulation of plasma prekallikrei n. These results suggest an important role for plasminogen activators in the inflammatory response during bovine mastitis. Using an enzyme-l inked immunosorbent assay we measured the plasminogen/plasmin level du ring the inflammation, but found a less than 2-fold increase during th e experimental period.