Human antithyroglobulin (anti-HTg) in serum and tissue cultures can be assayed by coprecipitation with 125I-labelled human thyroglobulin (HTg). Co-precipitation of the antibody from different sera gives roughly parallel curves, so that a standard serum can be used for quantitiation of other sera. By assessing the binding of 125I-labelled HTg in antigen excess we estimate the antibody content of the standard serum to be 0.14 ng anti-HTg per ml. Shortened incubation minimizes non-specific binding of HTg to serum globulins and obviates pre-assay absorption of HTg. Radioassay for thyroglobulin antibodies in serum correlated with values obtained by solid-phase competitive-binding assay (SPCB). One unit in our assay corresponds to 0.014 unit by the latter assay and to 0.12 units of MRC. Research Standard A. We confirm that serum thyroglobulin seriously interferes with SPCB assay, giving what appears to be positive results for anti-HTg where none is detected with our assay. Values for anti-HTg are depressed by serum HTg but only in the presence of very high concentrations in serum.
Antibodies Binding Sites, Antibody