EXPERIMENTAL EVIDENCES THAT ENDOGENOUS TS H MODULATES TOP ANTIGEN EXPRESSION - CLINICAL IMPORTANCE

The purpose of this work was to study if TSH has a role in TPO antigen expression in vivo. Using the cytotoxicity assay we measured TPO expr ession and correlated it with TSH serum levels in 3 groups of rats: co ntrol, hypothyroid and hypothyroid supplemented with thyroxine. For co mparative purposes, in the cytotoxicity assay we used rat monoclonal a ntiTPO or human sera with high titles for antiTPO antibodies. Hypothyr oid rats showed marked elevations of TSH serum levels and TPO antigen expression in their thyrocytes when compared to the control and supple mented group. A positive correlation between TPO antigen and TSH level s was observed (r = 0.69, p < 0.001). There was an excellent correlati on between TPO results using rat monoclonal or human sera antibodies ( r = 0.94 p < 0.0001). It is concluded that TSH modulates TPO antigen e xpression. These data are of clinical relevance considering that TSH m odulates the expression of other antigens that can maintain the immune response and perpetuate the immune disease in patients with Graves di sease treated with antithyroid drugs. Thus, the avoidance of TSH hyper secretion with administration of thyroxine could be useful to treat th ese patients.