Experimental autoimmune thyroiditis. I. Participation of IgA, IgM and IgG in the development of the disease.

Many factors have been shown to be important in the pathogenesis of experimentally induced autoimmune thyroiditis (EAT) in mice. However, the role of thyroid antibodies has not been clearly established. EAT was induced with rat Tg + LPS in RK mice. Two injections were given i.v. on days 0 and 7 and the antibody titre against rat and syngeneic Tg was determined in the weeks thereafter. Determination of the cellular infiltration of the thyroid, the presence of IgA, IgG and IgM in thyroid sections and electron microscope analysis of electro-dense deposits were also undertaken. Results show that (1) RTg + LPS is a potent inducer of autoimmunity with high antibody titer to RTg and MTg and 100% of the mice showed some degree of thyroid infiltrate on days 21 and 28; (2) immunofluorescence staining revealed that initially IgM is the main immunoglobulin and is later replaced by IgG. IgA is constantly present throughout the experimental period; (3) electro-dense deposits were found almost exclusively between the capillary basement membrane and the follicular basement membrane.