Simple and sensitive method for estimation of antithyroid plasma membrane antibodies in the serum of patients with autoimmune thyroid diseases; comparison with other assays

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Abstract
The ability of protein A from Staphylococcus aureus to interact with Fc fragments of IgG was used to estimate the antithyroid plasma membrane antibodiies in sera of patients with Graves'' disease. The results were expressed as an antithyroid plasma membrane antibodies (ATMA) index. The ATMA index estimated in 60 healthy blood donors varied from 0.,57-1.28, with a mean value of 0.99, SD O 0.20. The ATMA index in hyperthyroid untreated Graves'' disease varied from 1.80-8.0, with a mean value of 4.7. Autoantibody binding to thyroid plasma membranes could be inhibtied by (Fab)2 fragments obtained from the serum of patients with Graves'' disease but not by (Fab)2 fragments obtained from the serum of healthy blood donors. The influence of rabbit antithyroglobulin and antimicrosomal antibodies on the ATMA Index estimation was evaluated. The ATMA Index estimation was compared with the TSH binding inhibiting Ig (TBII) index and with the adenyl cyclase stimulating activity of Ig obtained from 92 hyperthroid Graves'' patients. The ATMA index was positive in 97%, the TBII Index in 62% and TSI in 35% of cases. This method using protein A could also be used for estimation of ATMA in other autoimmune thyroid disorders.