A new method of evaluating the heterogeneity of anti-insulin antibodies in sera from insulintreated diabetic patients is described. Sera from five insulin-treated diabetic subjects were treated with acid charcoal to remove endogeneous and/or exogeneous insulin, followed by neutralization of pH and incubation with 125I-insulin. After incubation with 125I-'nsulin, each serum sample was mixed with dextran-coated charcoal (DCC) solution in saline. With constant stirring, pH of the DCC solution was decreased stepwise, and dissociated 125I-insulin from antibodies was adsorbed to DCC.
The heterogeneity of anti-insulin antibodies regarding their binding ability of insulin was quantitatively expressed as 4pH90 20.that is, the pH span between 90% and 20% binding of 125I-insulitno the antibodie.s The relatives trength of antibodies against acid treatment is expressed as pH50%, that is, the pH value in which 50% of the bound 125I-insulinw as dissociated from the antibodies.The values of 4pH90 20 and pH50% varied from 0.84 to 1.89 and from 6.14 to 6.62 respectively.
Because the number of the sera investigated was small, the relationships between these parameters of anti-insulin antibodies and the duration and dose of insulin treatment are not clear at present. Further accumulations of data will clarify these relationships.
