In vitro- and ex vivo-derived cytolytic leukocytes from granzyme A X B double knockout mice are defective in granule-mediated apoptosis but not lysis of target cells

Abstract

Granzyme (gzm) A and gzmB have been implicated in Fas-independent nucleolytic and cytolytic processes exerted by cytotoxic T (Tc) cells, but the underlying mechanism(s) remains unclear. In this study, we compare the potential of Tc and natural killer (NK) cells of mice deficient in both gzmA and B (gzmAXB(-/-)) with those from single knockout mice deficient in gzmA ((-/-)), gzmB ((-/-)), or perforin ((-/-)) to induce nuclear damage and lysis in target cells. With the exception of perforin(-/-), all in vitro- and ex vivo-derived Tc and NK cell populations from the mutant strains induced StCr- release in target cells at levels and with kinetics similar to those of normal mice. This contrasts with their capacity to induce apoptotic nuclear damage in target cells. In gzmAXB(-/-) mice, Tc/NK-mediated target cell DNA fragmentation was not observed, even after extended incubation periods (10 h), but was normal in gzmA-deficient and only impaired in gzmB-deficient mice in short-term (2-4 h), but not long-term (4-10 h), nucleolytic assays. This suggests that gzmA and B are critical for Tc/NK granule-mediated nucleolysis, with gzmB being the main contributor, while target cell lysis is due solely to perforin and independent of both proteases. Show more