COMPARISON BETWEEN ANTIBODIES TO BOVINE AND HUMAN THYROTROPHIN (TSH) FOR RADIOIMMUNOASSAY IN PLASMA: CROSS REACTION STUDIES WITH CLINICAL RESULTS

Abstract

ABSTRACT The use of bovine and human TSH antisera for the measurement of human plasma TSH by radioimmunoassay has been investigated. The cross reaction between BTSH antiserum and plasma or pituitary HTSH as well as the species specificity of HTSH antiserum has been previously established. The effects of EDTA, of incubation time, of antiserum and precipitation serum dilutions on the formation of the hormone-antiserum complex were examined in both assays as well as the possible immunological reactivity of BTSH and HTSH antisera with ACTH, HGH, FSH, LH, HCG and HCS. It was observed that EDTA had no effect on the bovine TSH assay but allowed a faster binding of HTSH - HTSH antiserum, resulting in a short incubation period (2 days). A more diluted precipitating serum than usual was found to increase the precipitation of the antibody complexes in both assays. No cross-reaction occurred between the BTSH antiserum and human ACTH, HGH, HCS, FSH, LH and HCG. On the contrary, a significant displacement of the HTSH-131I-HTSH antiserum complex was observed with HGH, FSH, LH and HCG (even in low concentrations) but did not occur with ACTH or HCS. When higher levels of these hormones were added, a slightly greater displacement occurred but not in the same proportions. The values obtained in thyroid diseases by both radioimmunoassays are also reported and compared, but as the reference standards are not the same for both assays, absolute values could not be compared. Nevertheless the variations (increase or decrease) in plasma TSH levels in the different pathological conditions are in good agreement with both assays. Discrepancies were observed only in thyrotoxicosis and in some other cases presenting a slight increase in TSH with the human assay but not with the bovine assay. The bovine assay in the presence of other pituitary hormones has the advantage of exhibiting no cross reactions.