Interference of endogenous lactoperoxidase antibodies in a solid-phase immunosorbent radioassay for antibodies to protein hormones.

Abstract

Interference of endogenous antibodies to lactoperoxidase (EC 1.11.1.7) has been demonstrated in a solid-phase immunosorbent radioassay for the detection of antibodies to protein hormones. On enzymic iodination with lactoperoxidase, a little of the 125I is incorporated in the enzyme itself by self-iodination. Because the 125I-labeled lactoperoxidase was not removed from the tracer by chromatography on Sephadex G-50, G-100, and G-200 columns, endogenous antibodies to the enzyme, which were present in 25 of 28 sera from apparently healthy individuals, were detected in conjunction with the measurement of antibodies to growth hormone (somatotropin), prolactin, and thyroglobulin, thus causing false-positive results. Contaminating radioactive lactoperoxidase can be removed by adsorption chromatography on cellulose or by liquid chromatography, and can be avoided by performing the iodination with immobilized lactoperoxidase or with Chloramine-T.