A method for assaying antibodies to insulin that is based on the protection of insulin-I-131 from degradation by a liver extract is described. Moderately potent antibodies to insulin were obtained in rabbits by the injection of crystalline beef insulin, and a high degree of insulin resistance was demonstrable in some of the animals. The immunized animals did not become diabetic.

The biological activity of various insulin preparations was detected by their ability to lower the blood sugar of rabbits or through the stimulation of glucose uptake by the rat hemidiaphragm. Crystalline beef insulin and crude extracts of beef pancreas were effectively neutralized under the conditions of the tests whereas corresponding pork insulin preparations were incompletely neutralized in the rat hemidiaphragm assay. The insulin activity of sera from beef, pork, sheep and human sources was neutralized by the rabbit antisera.

The insulin activity of rabbit pancreas extracts and rabbit sera exhibited significant individual differences in the extent of neutralization. These observations on rabbit insulin preparations support the concept of Moloney and Coval that insulin of a given animal species can exist either in a “native” form that is not readily neutralized by antiserum produced in the same species, or an “altered” form that can be neutralized.

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