Soluble immune complexes (IC) can be detected in the serum of diabetic patients in frequencies ranging from 25 to 46%, depending on the screening technique used. Insulin-treated diabetics show a high frequency of insulin- anti-insulin IC (61% vs 4% in non-insulin treated patients) while other non-specific screening techniques show similar positivity frequencies in these two populations of diabetics. Soluble IC were isolated from the sera of 6 patients (5 under insulin treatment) using several

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... mbinations of polyethylene glycol precipitation, gel filtration and affinity chromatography. Sera from two normal donors was processed similarly and trace amounts of protein were recovered and used as controls. Platelet aggregation and release of ATP were studied with a Chronolog Lumi- aggregometer using platelet-rich plasma and low concentrations of ADP. All preparations of purified IC were found to induce platelet aggregation and ATP release of ADP sensitized platelets, while similarly obtained preparations from normal sera were inactive. Previous investigations had shown that sera from some diabetic patients contain factor(s) with platelet-activating properties. The present experiments suggest that soluble IC may be at least one of the factors.