Origin of fibrinolytic activity in cultures of the human kidney

In cultures of primary explants from human kidneys, a plasminogen activator was produced and released by cells which emerged from small vessels. By means of a histochemical fibrin slide technique the fibrinolytic activity was accurately localized to the active cells. No significant fibrinolytic activity was exhibited by tubular cells, fibroblasts, macrophages, or lymphocytes in the outgrowths. Plasminogen activator was also present in the culture media and the titer increased after repeated changes of fluid and as the interval between, refeedings was lengthened, indicating a continuous production and release of a plasminogen activator. These were found to be functions of living cells and were not observed in cells that died during culture. Preliminary immunological investigation of the identity of the plasminogen activator in the tissue culture media showed that it is identical to urokinase.