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

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Abstract
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. Analysis of in vivo activated T cells revealed that this particular proteinase was expressed in flow cytofluorometry sorted lymphocytic choriomeningitis virus-specific Lyt-2+, L3T4− cytolytic T lymphocytes but not in Lyt-2−, L3T4+T cells presensitized with either Listeria monocytogenes or I-A alloantigens. The data demonstrate that the two T cell subsets (Lyt-2+, L3T4−; Lyt-2−,L3T4+) have distinct in vitro induction requirements for the expression of proteinase and that after activation of T cells in vivo the enzyme is preferentially associated with Lyt-2+, L3T4−effector cells.