A Cytotoxic Proteinase Isolated from Human Lymphocytes

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Abstract
A proteinase active at physiologic pH was isolated from unstimulated human peripheral blood lymphocytes with gel filtration and affinity chromatography. The proteinase with a molecular mass of approximately 30,000 daltons was completely inhibited by diisopropylfluoro-phosphate (DFP) and soybean trypsin inhibitor (STI). Incubation of the lymphocyte enzyme with 3H-proline labeled T24 human bladder carcinoma cells resulted in significant cytotoxicity of the target cells. Cytotoxicity was only observed with much higher concentrations of trypsin. Similar results were obtained with a 51Cr release assay. This investigation demonstrates that unstimulated human peripheral blood lymphocytes contain a cytotoxic proteinase capable of killing pre-labeled target cells. The proteinase may be involved in lymphocytemediated cytotoxicity.