Isotypic distribution of human anti-thyroglobulin IgG antibodies: methodological difficulties

The subclass distribution of human anti-thyroglobulin IgG antibodies (TgAb) was studied in 24 sera using an indirect enzyme-linked immunosorbent assay (ELISA) with monoclonal anti-subclass antibodies. An IgG4/IgG1 predominance was found. TgAb were purified from seven sera by affinity chromatography. The antigen-specific indirect ELISA was repeated in the purified TgAb, in which IgG subclasses were measured by a competitive assay with monoclonal antibodies. The latter method showed an IgG2 predominance. Comparison of the results obtained by the three approaches showed discrepancies that probably reflect bias introduced by both the indirect ELISA and the affinity chromatography.