[Development of highly sensitive assays of antithyroid microsomal antibodies and their clinical application--solid type ELISA using the avidin-biotin system].

We have developed new type of ELISA using avidin-biotin (AB) system in measuring antithyroid microsomal antibody (AMA). In the first method, AMA was detected by biotinylated anti-IgG (Indirect AB-ELISA) and in the second AMA was detected by biotinylated microsome antigen (Sandwich AB-ELISA). In the both methods, avidin-peroxidase was then added and peroxidase activity remained on the wells of a microplate was measured. In the study of samples from patients with Graves' disease with negative MCHA test (n = 39) and normal controls (n = 19), Indirect AB-ELISA showed a higher OD492 in Graves' patients than normal controls (p less than 0.01), whereas Sandwich AB-ELISA did not. In the study of patients with chronic thyroiditis which was confirmed by fine needle aspiration biopsy, 7 out of 9 samples with negative MCHA test and all of 11 with weakly positive MCHA test were positive in the Indirect AB-ELISA. These studies demonstrated the superior sensitivity of Indirect AB-ELISA than the other methods. Then the samples from patients with various kinds of diseases and negative MCHA test were assessed using this method. Forty-eight in 60 cases (80.0%) of Graves' disease, 3 in 4 cases (75%) of chronic thyroiditis, 6 in 7 cases (85.7%) of simple goiter, 7 in 8 cases (87.5%) of thyroid cancer, 2 in 9 cases (22.2%) of thyroid adenoma and 1 in 6 cases (16.7%) of pituitary hypothyroidism showed AMA activity. Therefore, autoimmune phenomena are far more common in various thyroid diseases than it has been previously recognized.