Immunoprecipitation of TSH-TSH receptor complexes

The ability of Graves' sera to interact with the TSH receptor crosslinked to a 125I-labelled photoactive derivative of TSH has been investigated. Crosslinked complexes were prepared using non-purified detergent solubilized human thyroid and guinea pig fat TSH receptors. Affinity purified porcine TSH receptor preparations wee also used. After crosslinking, the crosslinked TSH-TSH receptor complexes were separated from aggregates and free TSH on Sephacryl S-300, incubated with test sera followed by immunoprecipitation using anti-IgG or Protein A. Using non-purified human TSH receptors crosslinked to TSH, a mean +/- SD of 12.1 +/- 4.9% of the crosslinked complex was immunoprecipitated with Graves' sera (n = 7) compared with 10.3 +/- 2.6% with Hashimoto sera (n = 6; P greater than 0.14) and 3.8 +/- 1.0% with normal sera (n = 6; P less than 0.004). These values were markedly reduced when TSH receptor preparations free of other thyroid autoantigens (guinea pig fat TSH receptors) were used. Under these conditions immunoprecipitation with Graves' sera (n = 24) was 1.6 +/- 1.3% compared with 0.8 +/- 0.6% for Hashimoto sera (n = 13) and 0.8 +/- 0.4% for normal sera (n = 12; P less than 0.003). In addition complexes formed between TSH and affinity purified porcine TSH receptors gave low immunoprecipitation values for Graves' (1.44 +/- 0.73%; n = 20) and Hashimoto sera (1.7 +/- 0.94; n = 11) which were not significantly different (P greater than 0.4). Overall, therefore, the effects of Graves' and Hashimoto sera were similar and the amounts of material immunoprecipitated were markedly reduced when TSH receptor preparations containing reduced amounts of other autoantigens were used. Consequently the Graves' sera did not appear to interact specifically with crosslinked TSH-TSH receptor complexes. However the Graves' sera studied did contain TSH receptor antibodies which could inhibit the binding of labelled TSH to TSH receptors in the preparations used and our results suggest that the binding of TSH and these antibodies to the receptor is mutually exclusive. There is considerable evidence that serum from patients with Graves' disease contains antibodies to the TSH receptor (Rees Smith, 1981). Several studies have suggested that binding of the receptor antibody and TSH to the TSH receptor is mutually exclusive (Manley et al., 1977; Petersen et al., 1977; Rickards et al., 1981) but recently the formation of termolecular complexes consisting of detergent solubilized receptors, labelled TSH and Graves' IgG has been reported (Konishi et al., 1982; De Bruin et al., 1984).(ABSTRACT TRUNCATED AT 400 WORDS)