LACK OF EFFECT OF ANTITHYROID DRUGS UPON TOP ANTIGEN EXPRESSION IN AUTOIMMUNE THYROID-DISEASE

The aim of this study is to determine whether antithyroid drugs (ATD) act via inhibiting thyroid hormone synthesis or by interfering with th e immune process which leads to autoimmune disease. Previously we had demostrated that ATD do not affect HLA-DR and TPO antigen expressions induced by appropriate stimulus in normal thyrocytes, so we decided to study what happens when the same experiments are performed using auto immune thyrocytes. Cultured thyroid tissue from patients operated on f or Graves' Disease or Hashimoto's Thyroiditis were stimulated with TSH or TBII alone or associated with ATD; TPO antigen expression was eval uated by the Citotoxicity Assay using human monoclonal antiTPO. When a utoimmune thyrocites were cultured and no stimulus was used or with th e addition of MMI or PTU alone, very low values of TPO expression were noted (8.6 +/- 6.7, 5.0 +/- 7.1 and 4.2% +/- 2.3% respectively); if t hey were stimulated with TSH or TBII, a sharp rise of TPO antigen expr ession was detected (54.4 +/- 23.3 and 62.6 +/- 16.5%), these figures being significantly different from unstimulated cells (p < 0.001). ff both stimulus were used associated with ATD, the high TPO antigen expr ession was unaffected. It is concluded that, at least in vitro, ATD ha ve no effect upon induced-antigen expression in autoimmune thyrocytes. Since they do not after antigen presentation, a primary step in the i mmune process, it is difficult to accept that their mechanism of actio n is through interference with the immune response.