Immunological properties of Tg carbohydrates: enhancement of Tg immunoreaction by removal of sialic acid.

Immunoreaction of desialylated and native thyroglobulin was compared in sera of patients with anti-thyroglobulin antibodies by radioimmunoassay with 125I-labelled thyroglobulin. Two human thyroglobulins were iodinated both in vivo and by lactoperoxidase. After desialylation enhancement of immunoreaction was observed in several sera ranging from marginal to more than 100%. The effect was not due to iodination since it was reproducible with desialylated thyroglobulin labelled in vivo. In one serum (B.P.) a marked enhancement was only seen with one thyroglobulin suggesting that desialylation may unmask isoantigens of thyroglobulin. Glycopeptides prepared from human thyroglobulin inhibited the immunoreaction between native thyroglobulin and autoantisera. The results indicate that sialic acid masks antigenic determinants in human thyroglobulin and that carbohydrates might be the determinants involved in the process of autoimmunization.