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A specific serine proteinase is inducible in Lyt‐2+, L3T4− and Lyt‐2−, L3T4+ T cells in vitro but is mainly associated with Lyt‐2+, L3T4− effector cells in vivo

Recently, we and others reported on the expression of a serine proteinase in long‐term cultured murine T lymphocyte cell lines. In an attempt to explore the distribution and possible regulation of this enzyme in T lymphocyte subsets, we performed the presented detailed study. We found that the proteinase is not expressed by thymocytes and resting T cells but can be induced by lectin or antigen in combination with lymphokine sources in vitro in macrophage‐depleted unselected T cells as well as in both T cell subsets (Lyt‐2+, L3T4−and Lyt‐2−, L3T4+) separated by flow cyto‐fluorometry. Furthermore, it appears that cell‐associated proteinase activity is increasing with prolonged culture period of sensitized T lymphocytes and that it is higher in antigen‐activated as compared to lectin‐activated T cells. When tested for substrate specificity the T cell‐associated proteinase was shown to preferentially cleave model peptide substrates carrying L‐arginine at position P1 in combination with nonpolar amino acids at position P2 and P3. As concluded from its sensitivity to proteinase inhibitors the enzyme can be classified as a serine proteinase and by molecular sieving at high ionic strength it was shown to have a mol. mass of ∼ 50–60 kDa.