Validation of the cytochemical section bioassay for thyroid stimulating antibodies.

: A cytochemical bioassay for thyroid stimulators which utilised 12 micrometer sections of guinea pig thyroid as the target tissue was validated and applied to the measurement of thyroid stimulating antibodies (T.S.Ab.) in human plasma. T.S.H. and T.S.Ab. could be distinguished in the assay by the times at which they produced maximal responses; 90 seconds for T.S.H. and 180 seconds for T.S.Ab. Homogeneity of responses to stimulation was relatively uniform throughout thyroid tissue enabling simultaneous measurement of several plasma samples per guinea pig. Sensitivity of the assay was 1.5 x 10(-9) microU/l MRC L.A.T.S.-B. Antiserum to H-T.S.H. produced no significant change in T.S.Ab.-like activity when added to plasma from a thyrotoxic patient. Both anti-IgG and aliquots of a homogenate of thyroid tissue from a thyrotoxic patient diminished responses of thyrotoxic plasma in a concentration dependent manner. T.S.Ab. was present at titres of 1/100 to 1/100,00 in 13 hyperthyroid patients tested to date.