Increased sensitivity of triiodothyronine antibodies for radioimmunoassay after removal of endogeneous antigen by simple laboratory procedures

Conventionally produced antibodies against triiodothyronine (T3) are known to possess high amounts of endogenously produced T3 associated with them. We felt that such antibodies would work better for T3 radio-immunoassay (RIA) after prior removal of the antigen. We attempted dissociation and subsequent removal of T3 from antisera by two different methods, viz. dialysis and alcohol extraction. It was possible to remove T3 to an extent of 77% by alcohol extraction and 60% by dialysis. Resultant antisera fail to demonstrate any increase in the titre. However, when standard curves were generated using these antisera, the assays become more sensitive and it was possible to detect T3 in concentrations as low as 6.25 pg. The affinity constants of these antisera calculated from the respective Scatchard plots were found to have increased after both dialysis treatment as well as alcohol extraction. This was thought to be due to rendering some of the high affinity binding sites on the antibodies free of antigen after treatment. Serum T3 levels were measured in 68 patients with various thyroid status using both treated as well as untreated antiserum. The difference between the average values of serum T3 concentration estimated using various antisera before and after the treatment was not statistically significant. (author)