A cytotoxic proteinase isolated from human lymphocytes

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 diisopropylfluorophosphate (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 lymphocyte-mediated cytotoxicity.