Functional significance of Syntaxin 8 in Cytotoxic T Lymphocyte cytotoxicity (122.3)

Abstract

Abstract Cytotoxic T Lymphocytes (CTLs) are activated CD8+ T cells which identify and kill pathogen infected, tumor and nonself cells by FAS ligand expression and by secretion of perforin and granzymes from lytic granules specifically at the immunological synapse (IS). This prevents killing of healthy bystander cells. Therefore at the time of killing these cytotoxic molecules are to be delivered to the IS. SNAREs are membrane associated proteins involved in vesicle transport, docking and fusion. Mutations of these proteins can cause diseases like Familial Hemophagocytic Lymphohistiocytosis. We have shown previously that Vti1b is required for docking of lytic granules at the IS. We also found that Vti1b and Syntaxin 8 (Stx8) colocalize with perforin in human CTLs. Further experiments showed that Stx8 partially colocalized with Vti1b. To elucidate the role of SNAREs in CTL cytotoxicity, siRNA were used to downregulate their expression. Stx8 downregulation did not impair the IS formation as CD3 accumulation at the IS was unaffected. We have previously shown that the killing capacity of CTLs is impaired by Vti1b downregulation. Here, Stx8 downregulated CTLs used in real time killing assay showed reduction in killing. Cycloheximide treatment of control and Stx8 downregulated CTLs showed that Stx8 is required for killing by perforin secretion. This conclusion is also supported by our preliminary ELISA data, which shows reduced perforin secretion in Stx8 downregulated CTLs.