A sensitive assay was used to measure the binding of iodine-125-labeled insulin in serum obtained from 112 newly diagnosed insulin-dependent diabetics before insulin treatment was initiated. Two groups of nondiabetics served as controls: children with a variety of diseases other than diabetes and nondiabetic siblings of insulin-dependent diabetics. Eighteen of the diabetics were found to have elevated binding and 36 were above the 95th percentile of control values. The insulin-binding protein is precipitated by antibody to human immunoglobulin G, has a displacement curve that is parallel and over the same concentration range as serum from long-standing insulin-dependent diabetics, and elutes from a Sephacryl S-300 column at the position of gamma globulin. These insulin antibodies are present in a large percentage of newly diagnosed, untreated diabetics and may be an immune marker of B-cell damage.

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Use of pure porcine insulin versus partially purified insulin of bovine/porcine origin might be expected to have certain clinical benefits, e.g., a lower incidence of skin reactions, a lower insulin dosage, better diabetes regulation, and greater preservation of endogenous insulin secretion. To test this hypothesis, we randomly assigned 112 newly diagnosed, untreated, insulin-dependent diabetic children to therapy with either pure porcine or partially purified bovine/porcine insulin. They were followed for 1 yr, data being available on at least 90 subjects at each visit. More skin reactions were found in the group treated with the bovine/porcine insulin. This insulin was of higher antigenicity, and binding of radiolabeled insulin (mean +/- SE) by serum from bovine/porcine insulin treatment was 35.5 +/- 2.6 versus 16.8 +/- 1.4% (P less than .001) for pure porcine insulin treatment 12 mo after initiation of insulin therapy. However, throughout the 12 mo of observation the levels of glycosylated hemoglobin, insulin dosage, fasting plasma glucose, and C-peptide concentration were similar for the groups. Reported incidences of hypoglycemia and nocturia were also similar. Thus, insulin-antibody formation and skin reactions were minimized by the use of pure porcine versus partially purified bovine/porcine insulin, but no other clinical advantages were apparent.

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