Experimental autoimmune thyroiditis induced by a 5-10-kDa tryptic fragment from porcine thyroglobulin.

Monoclonal autoantibodies obtained using the native porcine thyroglobulin (Tg) molecule for immunization were shown to react against a defined epitope of the Tg molecule. Its biochemical characterization was undertaken, using trypsin treatment of Tg, followed by gel filtration, affinity chromatography, sodium dodecyl sulfate-polyacrylamide gel electrophoresis and high pressure liquid chromatography analysis. Immunoreactivity tested by immunoblotting with appropriate monoclonal anti-Tg antibody allowed the detection of one peptide fragment of 5-10 kDa, after limited proteolysis with trypsin. We demonstrated that this peptide reacts exclusively with monoclonal anti-Tg antibodies which block in vitro proliferative T cell response; moreover, the 5-10-kDa tryptic fragments from porcine Tg were able to induce thyroiditis when injected into normal CBA mice, while porcine Tg depleted from these fragments was not able to do so.