Abstract
Plasminogen activator (PA), an enzyme which is secreted in large quantities by certain types of tumour cells, is an apparent lymphocyte mitogen. Treatment of mouse spleen cells with anti-Thy-1.2 serum plus complement prevents responsiveness, indicating that T cells are being stimulated to divide. In addition to the foregoing, we have shown that PA has the capacity to interfere with certain types of cell-mediated cytotoxicity and natural killer cell reactions in which tumour cells are employed as targets. These results suggest that PA may play an immune-modulating role which may be of importance in tumour self-defense.
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