Development of a radioimmunoassay for triiodothyronine sulfate

This paper is the first description of a radioimmunoassay (RIA) for triiodothyronine sulfate (T3S). Rabbits were immunized against T3S coupled to bovine serum albumin using carbodiimide. All animals produced antibodies to T3S but also even higher titers of T3 antibodies. Ka values for binding of T3 and T3S to these antisera varied between 2 x 10(10) and 8 x 10(10) M-1. One of the antisera (#8193) was selected for use in the T3S RIA because of a high titer of T3S antibodies (final dilution 1:50,000), a high sensitivity to T3S (less than 2.5 fmol/tube), and a low crossreactivity by T3 (0.4%). This RIA provides a tool for the study of the importance of sulfation as a metabolic pathway for T3.