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We recently described a solid phase immunoradiometric assay (IRMA) for anti-thyroglobulin and anti-thyroid microsomal antibodies. In the present study a similar IRMA for gastric parietal cell antibodies (PCA) has been developed. Samples to be tested are incubated within wells of polyvinyl microtitre plates coated with solubilized gastric microsomal antigen. After removal of unbound material, PCA is detected by adding purified 125I-anti-human IgG antibody. A good correlation was found with the results of PCA assays obtained by indirect immunofluorescence. In contrast, negative PCA by IRMA were consistently obtained in sera containing high titres of several other organ specific and non-organ specific autoantibodies. PCA determinations by IRMA were than carried out in a series of normal controls and patients with autoimmune or non-autoimmune thyroid disorders. Positive results were obtained in three of 70 (4.3%) apparently normal subjects, in 16 of 87 (18.4%) patients with Hashimoto's thyroiditis, in 10 of 48 (20.8%) with idiopathic myxoedema. in 25 of 95 (25.6%) with Graves' disease and in five of 64 (7.8%) with other non-autoimmune thyroid disorders. Preliminary results showed that quantitative measurements of PCA by IRMA could be performed using a serum containing high levels of PCA as standard reference. In conclusion, PCA may be easily and specifically detected using the same IRMA procedure previously developed for anti-thyroid antibodies. We therefore suggest that the present IRMA may be proposed as a general technique for the detection of different organ specific autoantibodies. [ABSTRACT FROM AUTHOR]

Parallel measurements of circulating anti-thyroid microsomal (anti-M) antibodies by radioassay and haemagglutinatinn were performed on subjects with or without thyroid disorders. Three quarters (75.4%) of control subjects had undetectable antibody levels (< 10 u/ml) by radioassay and only 3.1% had concentrations of &ges; 75 u/ml. Abnormally elevated levels (&ges; 75 u/ml) were found in most of the patients with Hashimoto's thyroiditis (94.1%) or idiopathic myxoedema (86.7%), in the majority (75.0%) of those with Graves' disease and only in a minority of those with other thyroid disorders. The percentage of positive sera by haemagglutination was verisimilar in all groups to that of abnormal values observed in the radioassay. Direct comparison of parallel tests on a total of 631 sera revealed a highly significant correlation (r = 0.91, P < 0.001) between the two methods, but elevated antibody titres by haemaegglutination were found in some sera with negative radioassays. All these sera were from a single patient with thyroid carcinoma associated with Hashimoto's thyroiditis and had elevated levels of anti-thyroglobulin (anti-Tg) antibodies. Evidence that such discrepancies were due to anti-Tg antibodies reacting with microsomal-bound Tg was provided by the demonstration that the haemagglutination produced by these sera could be completely inhibited by the addition of Tg. A similar inhibition was observed with two rabbit antisera to human Tg, but not with sera from patients with thyroid autoimmune disorders containing high levels of anti-microsomal anti-bodies. [ABSTRACT FROM AUTHOR]