Flourescence-activated cell scanning analysis of human blood cells revealed novel urokinase receptors in large granular lymphocytes and a small subset of T-cells (CD3+). Culturing of T-cells with interleukin-2 to generate CD3+ lymphokine-activated killer cells caused a large increase in urokinase binding, suggesting that the urokinase receptor is an activation antigen. The receptor in lymphocytes was similar to that in monocytes with regard to size, affinity and ligand specificity, but did not mediate degration of urokinase-inhibitor complexes. It is suggested that lymphocyte-bound pro-urokinase is activated, e.g. by the human T-cell specific serine proteinase. HuTSP-1, and thereby starts a cascade of plasminogen activation important for extravasation of the cells.
