Both CD4⁺ and CD8⁺ T-Cells in Syngeneic Islet Grafts in NOD Mice Produce Interferon-γ During β-Cell Destruction

Syngeneic pancreatic islet grafts in diabetic NOD mice are infiltrated by mononuclear leukocytes, β-cells are selectively destroyed, and autoimmune diabetes recurs. This model was used to identify islet graft-infiltrating mononuclear leukocytes associated with β-cell destruction and diabetes recurrence. We compared cell surface antigen and cytokine-producing phenotypes of mononuclear leukocytes in islet grafts from NOD mice that were protected from diabetes recurrence by complete Freund's adjuvant (CFA) administration (β-cell nondestructive insulitis) and in islet grafts from control phosphate-buffered saline (PBS)-injected NOD mice (β-cell destructive insulitis). Islet grafts from CFA-injected mice contained fewer CD4⁺ and CD8⁺ cells and more B cells; also fewer interferon gamma (IFN-γ), interleukin-2 (IL-2), and tumor necrosis factor alpha (TNF-α)-positive cells and more IL-4 and IL-10 positive cells. By performing two-color immunostaining of cell surface antigens and intracellular IFN-γ, we found that IFN-γ positive cells in islet grafts from CFA- and PBS-injected mice were ∼ equally divided between CD4⁺ and CD8⁺ T-cell subsets. Also, the frequencies of both CD4⁺ IFN-γ⁺ and CD8⁺ IFN-γ⁺ cells were decreased in islet grafts from CFA-injected mice. These findings suggest that destruction of β-cells in syngeneic islets transplanted into NOD mice is promoted by cells producing Th1-type cytokines (IFN-γ, IL-2, and TNF-α) and prevented by cells producing TH2-type cytokines (IL-4 and IL-10). Furthermore, both CD4⁺ and CD8⁺ IFN-γ-producing T-cells in the islet grafts appear to be involved in β-cell destruction and diabetes recurrence.