Effectiveness of different methods to eliminate interference by thyroglobulin antibodies in the ELISA for thyroid microsomal autoantibodies.

ABSTRACT

Thyroid microsomal autoantibodies (TMA) have been mostly detected by means of either immunofluorescence (IF), tanned red cell haemagglutination (TRCH), or radioimmunoassay (RIA) until the recent development of ELISA. False positives in the ELISA for the detection of TMA due to interference by thyroglobulin antibodies (TGA) present in some test sera reacting with thyroglobulin (Tg) present as a contaminant in the thyroid microsomal preparation (TMP) appears to be common. In this study we tried various ways of removing any Tg contaminant in the TMP by further gel filtration, affinity chromatography of the microsomal preparation or preincubation of the test sera with either Tg or Tg-sepharose 4B immunoadsorbent to absorb out TGA present in the sera. Further gel filtration and affinity purification of the TMP failed to totally remove all the contaminating Tg. Preincubation with Tg effectively removed any TGA present in the test sera but resulted in inhibition of the TMA-thyroid microsomal antigen reaction in the test sera including those without TGA. Preincubation with Tg-immunoadsorbent equally effectively absorbed out any TGA present in the test sera but without significant inhibition of the assay reaction in TGA-free sera. The preincubation of the TMP with Tg-immunoadsorbent is an effective way of removing TGA present in sera without inhibiting the test reaction and thus resulting in false negatives especially in low-titre sera as occurs with the presence of free Tg in the test system.