DIPEPTIDYL PEPTIDASE-I IS ENRICHED IN GRANULES OF INVITRO-ACTIVATED AND INVIVO-ACTIVATED CYTOTOXIC T-LYMPHOCYTES

Recent studies have suggested that dipeptidyl peptidase I (DPPI) is th e major post-translational processing enzyme responsible for generatin g activated myeloid and lymphoid granule serine proteases. The current studies assessed the relative levels of DPPI and granzyme A (BLT este rase) in B6 anti-H-2d-specific CTL generated in mixed lymphocyte cultu res (in vitro-activated CTL), by infusion of B6 spleen cells into irra diated H-2d mice (graft-vs-host, GVH CTL) or by 1-degrees and 2-degree s peritoneal immunization of B6 mice with P815 (H-2d) cells (PE CTL). In contrast to low levels of DPPI activity in unstimulated CD4+ spleen T cells, both unstimulated CD8+ spleen T cells and in vitro-activated CTL populations were several-fold enriched in DPPI activity, while PE CTL and GVH CTL expressed even higher levels of DPPI. Depletion of DP PI-enriched cells by treatment with Leu-Leu-OMe resulted in loss of cy tolytic effector function from each CTL population. However, PE CTL an d GVH CTL were more sensitive to the toxicity of Leu-Leu-OMe than were in vitro-activated CTL. While standard BLT esterase assays detected m uch higher levels of this serine protease activity in GVH CTL or in vi tro-activated CTL than in PE CTL, levels of BLT esterase activity sign ificantly above the basal levels present in unstimulated CD8+ or CD4T lymphocytes were found in association with immunoreactive granzyme A in lysates of PE CTL. In both PE CTL and in vitro-activated CTL, DPPI and BLT esterase activity co-localized in the granule fraction of cel l lysates, and similar percentages of total cellular BLT esterase and DPPI were exocytosed upon cross-linking of surface CD3. Thus, both in vivo- and in vitro-activated CTL were found to possess functional gran ules containing readily detectable albeit somewhat different levels of DPPI and granzyme A activity.