The Exocytosis of Lytic Granules Is Impaired in Vti1b- or Vamp8-Deficient CTL Leading to a Reduced Cytotoxic Activity following Antigen-Specific Activation

R. Dressel, L. Elsner, P. Novota, N. Kanwar, G. Fischer von Mollard
2010 Journal of Immunology  
The exocytosis of cytotoxic proteins stored in lytic granules of activated CTL is a key event during killing of target cells. Membrane fusion events that are mediated by soluble N-ethylmaleimide-sensitive-factor attachment protein receptor (SNARE) proteins are crucial, as demonstrated by patients with familial hemophagocytic lymphohistocytosis type 4 who have mutations in the SNARE protein syntaxin-11 that result in an impaired degranulation of cytotoxic cells. We found an increased mRNA
more » ... creased mRNA expression of the SNARE protein genes Vti1b and Vamp8 during Ag-specific activation of CTL from TCR-transgenic OT-I mice. Therefore, we investigated the cytolytic activity of CTL from TCR-transgenic Vti1b and Vamp8 knockout mice. At 3 d as well as at 4 d of Agspecific stimulation, the degranulation of CTL was significantly reduced in Vti1b and Vamp8 knockout mice, as determined by cell surface expression of the degranulation marker CD107a. After 3 d of Ag-specific stimulation, the cytolytic activity of Vti1b-and Vamp8-deficient CTL was reduced to 50% compared with heterozygous controls. However, 4 d after stimulation, the cytotoxic activity of Vti1b-as well as Vamp8-deficient CTL was not impaired anymore. The capacity of Vti1b-and Vamp8-deficient dendritic cells to process Ags and to stimulate the proliferation of CTL was not reduced, arguing against an indirect effect on the activation of CTL. These findings suggest a role of the SNARE proteins vti1b and vesicle-associated membrane protein 8 in the degranulation of CTL. However, a deficiency can apparently be compensated and affects only transiently the cytotoxic activity of CTL during their development to armed effector cells. Abbreviations used in this paper: ct, cycle threshold; DC, dendritic cell; FHL, familial hemophagocytic lymphohistiocytosis; LAMP1, lysosomal-associated membrane protein 1; MFI, mean fluorescence intensity; SNAP-23, synaptosomal-associated protein-23; SNARE, soluble N-ethylmaleimide-sensitive-factor attachment protein receptor; VAMP, vesicle-associated membrane protein.
doi:10.4049/jimmunol.1000770 pmid:20543108 fatcat:oqil2cwexbggfpjvnespgdbtce