Analysis of antibody-dependent cell-mediated cytotoxicity in autoimmune thyroid disease

There is no consensus on the role of antibody-dependent cell-mediated cytotoxicity (ADCC) in autoimmune thyroid disease; recent reports have suggested that antibodies mediating ADCC are found particularly in patients with primary myxoedema, occur less frequently in Hashimoto's thyroiditis and are absent in Graves' disease. Using an ADCC assay with a single source of effector and target cells, and expressing results as lytic units, we have found antibodies capable of mediating ADCC in 9 of 17 patients with primary myxoedema, 9 of 22 patients with Hashimoto's thyroiditis and 6 of 22 patients with Graves' disease. There was no significant difference between the groups in this distribution. Mean levels of ADCC activity were not significantly different comparing primary myxoedema and Hashimoto's thyroiditis patients, although levels were lower in Graves' disease patients compared to those with Hashimoto's thyroiditis (P < 0.05). There was no correlation between TPO antibodies (total IgG or IgG subclasses) measured by ELISA and ADCC activity. These results suggest that thyroid antigens besides TPO are involved in ADCC and that antibodies mediating ADCC are not restricted to subgroups of patients with autoimmune thyroid disease.