Expression of bcl-2, Bax and Fas in oxyphil cells of Hashimoto thyroiditis.

Immunoreactivity for bcl-2, Bax and Fas was analysed in 16 cases with Hashimoto thyroiditis. Bcl-2-expression was constantly seen in regular thyrocytes and in the mantle-zone of lymphofollicular infiltrates. However, thyrocytes in the vicinity of lymphoid infiltrates and, especially, mitochondria-rich oxyphil cells exhibited reduced staining or none at all for bcl-2. Bax was found to be weakly reactive or negative in normal thyrocytes and was not up-regulated in bcl-2-deficient epithelial cells. In contrast, expression of Fas was markedly increased both in typical thyrocytes and in oxyphil cells within areas of lymphocytic infiltration. In conclusion, focal lack of bcl-2 expression together with up-regulation of Fas is a constant feature of Hashimoto thyroiditis. The reaction pattern of oxyphil cells is identical to that of affected typical thyrocytes without proliferation of mitochondria. Loss of bcl-2 with up-regulation of Fas is therefore likely to precede oncocytic change. Whether these alterations are involved in the process of oncocytic transformation remains to be clarified, however.