Detection of anti-thyroid plasma membrane antibody in patients with various thyroid diseases by solid phase enzyme-immunoassay

Abstract

Antibodies against thyroid cell surface antigens have been demonstrated by indirect immunofluorescence on viable cells and by mixed hemadsorption using monolayer cell culture. Recently quantitative assays using thyroid plasma membrane or cultured thyroid cell were also reported. The present study reports a novel quantitative assay for the detection of anti-thyroid plasma membrane antibody (APA) using solubilized and immobilized thyroid plasma membrane. Thyroid plasma membrane purified by sucrose density gradient centrifugation was solubilized with Triton X-100 and coupled to CNBr activated Sepharose 4B. Sera from patients with various thyroid diseases were incubated with this solid phase. Five microliters of serum was sufficient for the assay. After extensive washing, immunoglobulin G (Ig G) or immunoglobulin M (Ig M) bound to thyroid plasma membrane was detected by horseradish-peroxidase labeled rabbit anti-human Ig G or Ig M antibody. Significantly elevated values of Ig G class APA (Ig G-APA) were detected in the sera from patients with Graves' or Hashimoto's disease. Some of the patients with thyroid adenoma also showed positive Ig G-APA, although all of the patients with thyroid cancer had negative Ig G-APA. A significant correlation between Ig G-APA and anti-thyroid microsomal antibody (AMA) among patients with autoimmune thyroid diseases was observed. No significant correlation, however, was found between anti-thyroglobulin antibody (ATA) and Ig G-APA. A large amount of thyroglobulin (Tg), which was reported to have the receptor in thyroid plasma membrane, inhibited the binding of Ig G-APA does dependently. Ten micrograms of ATA and one milligram of bovine serum albumin, however, had no influence on the binding. Ig G-APA also significantly correlated with thyrotropin binding inhibitor immunoglobulin (TBII). The binding, however, was not inhibited by one hundred milliunits of TSH. These findings suggested that most of Ig G-APA was bound to different sites from TSH receptor, although some part of Ig G-APA might have TBII activity. Ig M class APA (Ig M-APA) among various thyroid diseases was also detected. In Graves' disease, more than sixty percent of patients had positive Ig M-APA. There was no significant difference in the value of Ig M-APA between untreated and treated patients. Positive Ig M-APA was found even in some euthyroid patients. Ig M-APA in Graves' disease correlated with neither AMA nor TBII. Some of patients with Hashimoto's disease and subacute thyroiditis also showed positive Ig M-APA.(ABSTRACT TRUNCATED AT 400 WORDS)