Demonstration of anti-"a-component" antibody--a possible means to differentiate patients with auto-antibodies to endogenous insulin from insulin-treated patients.

The presence of anti-"a-component" antibody was examined in sera of 4 groups of patients with or without anti-insulin antibody, using 125I-a-component and the polyethylene glycol precipitation method. 125I-a-component crossreacted with insulin antibody. This cross-reactivity was abolished after preincubation of these sera with monocomponent insulin. The specificanti-"a-component" antibody could be estimated in this procedure. After preincubation with monocomponent insulin, significant binding of 125I-a-component was demonstrated in sera of most patients treated with ordinary commercial insulin, but not in sera of 2 hypoglycemic patients suspected of an insulin autoimmune syndrome. Some cases treated with commercial insulin for less than one year and all cases treated with monocomponent insulin for 7-10 months did not have significant anti-"a-component" antibody. The test for the presence of anti-"a-component" antibody is not definitive but if positive it differentiates "auto-antibodies" from the antibodies produced by injections of commercial insulin.