Involvement of humoral and cellular autoimmunity in the pathogenesis of insulin-dependent diabetes mellitus (IDDM) is demonstrated by the presence of circulating autoantibodies and the early pancreatic lesion of insulitis. In an effort to detect the early pancreatic lesion in acute onset IDDM, we have labeled peripheral blood lymphocytes with indium oxine 111, reinjected these autologous cells intravenously into the patients, and followed their kinetics over 96 h using an emission computerized tomography (ECT) scanner. The reinjected cells are acutely distributed in the patients' lungs, liver, and spleen (2–12 h). At 24, 48, and 72 h, the labeled lymphocytes are no longer detectable in the lungs or the liver, but are clearly present in the spleen and in the pancreas. Lymphocytic pancreatic infiltration was observed in two of three acute-onset IDDM patients, but not in large number of patients undergoing similar scans for other diseases, suggesting ongoing mononuclear cell infiltration of the pancreas, a possible marker of the lesion of insulitis. Lymphocyte scanning may provide a powerful noninvasive tool for studying patients with IDDM and for selecting those who might benefit from immunosuppressive therapy.

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