Electron microscopy of monoclonal antibody-linked chains of thyroglobulin molecules

Negative staining electron microscopy visualized immune complexes of hog thyroglobulin produced by 3 monoclonal antibodies, each towards a different conformation-dependent antigenic structure of the thyroglobulin. Equimolar mixtures of the thyroglobulin and any one of the 3 antibodies formed peculiar unbranched chains of 'ovoid' thyroglobulin molecules linked by the antibody molecules in an 'end to end' fashion. A mixture of the thyroglobulin and the 2 different antibodies produced branched chains. A set of 3 conformation-dependent antigenic structures was thus located near each end of the elongated thyroglobulin molecule. The results also indicated a topological similarity between the 2 subunits of thyroglobulin.