Thyrotropin stimulates specifically the expression of the autoantibody binding domains of the thyroperoxidase molecule

To get some insight on the in vitro effect of TSH on the expression of two thyroid specific antigens (thyroglobulin (Tg) and thyroid peroxidase (TPO)) on the cell surface of cultured human thyroid tells an indirect immunofluo rescence-activated cell sorter (FACStar IV, Becton-Dickinson) was used. Onl y half of the cultures responded to TSH by increased surface expression of the thyroid specific antigen Tg, In these cells, TSH stimulation of TPO exp ression showed a difference in epitopes recognized by murine monoclonal ant ibodies. Epitopes of domain D, recognized by monoclonal antibody 1, 30, 40 and 53 which are not involved in autoimmunity, mere unaffected by TSH stimu lation, (n = 2-10), In contrast, TSH regulated the surface expression of th e TPO epitopes recognized by monoclonal antibody 15, 18, 24 and 60, which a re known to be related to the serum autoantibody binding domain of TPO, (n = 6-8; p < 0,05), This indicated that increased activity of the thyroid cel ls selectively stimulated the expression of autoantigenic epitopes on the c ell surface and supports the concept that increased cellular activity might predispose to the autoimmune processes leading to autoimmune thyroid disea se.