This study has used in vitro techniques to investigate the potential interactions between mouse pancreatic islet cells and syngeneic macrophages (M phi). Islets strongly stimulated M phi migration from agarose microdroplets; insulin was the only one of four islet cell hormones tested that was effective individually. Chronic exposure of islet monolayers to recombinant mouse IL-1, an M phi secretory product, was not cytolytic, but inhibited insulin secretion, reduced intracellular insulin content, and produced beta cell-specific degranulation. These effects were unique to IL-1; another monokine, tumor necrosis factor, as well as the lymphokine IL-2, and lymphotoxin were all without effect on insulin secretion or monolayer viability at the concentrations tested. The potential pathological consequences of the chemoattractive action of insulin on M phi, and the inhibitory effect of IL-1 on insulin secretion, are discussed.

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