Role of Inflammatory Infiltrate in Activation and Effector Function of Cloned Islet Reactive Nonobese Diabetic CD8 super(+) T Cells: Involvement of a Nitric Oxide-Dependent Pathway

To investigate how CD8 super(+) T cells interact with beta cells and local inflammatory cells in islets, we have isolated CD8 super(+) T cell clones from nonobese diabetic (NOD) spleen that recognize and destroy both islets and the NOD insulinoma cell line NIT-1. The clones destroyed NOD islets with pre-existing inflammation better than islets without signs of inflammation. Islets from NOD-scid mice were destroyed only poorly, but that could be improved by adding IL-7 to the assay. Anti-IFN- gamma Abs inhibited destruction of infiltrated islets. Single islets were effective stimulators of IFN- gamma production by cloned CD8 super(+) T cells, which varied >50-fold depending on the degree of islet infiltration. This effect of the islet mononuclear infiltrate could be mimicked by adding spleen cells to NIT-1 cells, which augmented IFN- gamma production above the level stimulated by NIT-1 cells alone. The enhancing effect of spleen cells could be attributed to their macrophage subpopulation and was not MHC restricted, although recognition of islet Ag by cloned CD8 super(+) T cells and subsequent islet destruction was restricted to islets expressing H-2D super(b) molecules. An inhibitor of inducible NO synthase inhibited destruction of inflamed islets by cloned CD8 super(+) T cells. We propose that macrophages in inflamed islets provide a form of bystander costimulation of beta cell-specific CD8 super(+) T cells. CD8 super(+) T cells respond to Ag and costimulation by producing IFN- gamma that activates macrophages. Activated macrophages facilitate islet destruction by CD8 super(+) T cells through a NO synthesis-dependent pathway.