Fas and Fas-ligand expression in seminomatous testes

Sixteen seminomas with surrounding tissue containing normal and precancerous (cis) seminiferous tubules were examined for the expression of Fas (CD95, APO-1) and Fas ligand (FasL) (CD95L). This was done by analyzing frozen specimens using immunohistochemistry with antibodies directed against Fas and FasL. The study showed that varying numbers (mean approx. 20%) of Fas-positive lymphocytes were present among tumor-infiltrating lymphocytes, but very few FasL-positive lymphocytes. Fas was not expressed by normal seminiferous tubules and only occasional Fas-positive epithelial cells were seen in cis tubules. FasL was expressed in 9 out of 10 cases in virtually all normal seminiferous tubules, mainly as a thin layer at the base of the seminiferous epithelium. In precancerous tubules, this layer was discontinuous and less pronounced. Rete testis expressed FasL in 2 out of 2 cases with rete present and Fas in 1 out of 1 case. Invasive tumor cells did not express Fas or FasL. The data are discussed in relation to immune reactions to seminomas and to the concept of the testis being an immunologically privileged area.