An assay was developed to detect the cytotoxic effects of cytokines on rat pancreatic islet cells in monolayer culture. Cell lysis was detected by a 51Cr-release assay after 4 days of incubation with various cytokines. When tested alone, murine (rat and mouse) interferon-γ (mIFN-γ) produced a small dose-dependent lysis of islet cells; human IFN-γ, mouse IFN-α/β, interleukins 1 and 2 (IL-1 and IL-2), tumor necrosis factor (TNF), and lymphotoxin (LT) were inactive. When added together, the following combinations of cytokines showed synergistic cytotoxic effects: TNF (or LT) plus IL-1, TNF (or LT) plus mIFN-γ, and IL-1 plus mIFN-γ. These results indicate that the cytokine products of mononuclear cells of the immune system, IFN-γ, TNF, LT, and IL-1 have strong synergistic cytotoxic effects on islet cells and therefore may act as direct chemical mediators of islet β-cell destruction in type I (insulin-dependent) diabetes.

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