Preferential utilization of the perforin/granzyme pathway for lysis of Epstein-Barr virus-transformed lymphoblastoid cells by virus-specific CD4⁺ T cells

In this report, we show that Epstein-Barr virus (EBV)-infected lymphoblastoid cell lines (LCL) express Fas and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) receptor 2 and that LCL are lysed following engagement of these receptors by agonist Fas and TRAIL receptor-specific monoclonal antibodies (MAb). We also show that EBV-specific CD4⁺ T cells mediate bystander lysis of susceptible targets through both the Fas/Fas ligand (FasL) and the TRAIL pathways, but find that the dominant mechanism of lysis following cognate, HLA class II-restricted recognition of LCL is the perforin/granzyme pathway. Killing of LCL by EBV-specific CD4⁺ T cells was strongly inhibited by concanamycin A, an agent that elevates granule pH, resulting in accelerated destabilization and degradation of perforin. In contrast, blocking anti-FasL MAb showed only limited inhibition of LCL killing. Blocking anti-TRAIL MAb had no effect on lysis of LCL by EBV-specific CD4⁺ T cells. We further show that culture of EBV-specific CD4⁺ T cells in the presence of interleukin 4 markedly abrogates effector cytotoxic function against LCL through direct depletion of intracellular perforin, with no evidence of a Th1 to Th2 shift in patterns of cytokine expression.