Reproductive biology. Cytotoxic phenotype of intra-epithelial lymphocytes in normal and cryptorchid human testicular excurrent ducts

BACKGROUND: Most testicular and epididymal lymphocytes express T-cell markers, but their cytotoxic potential and activation status have not been reported. In this study, distribution of the cytotoxic cells was compared between normal and cryptorchid testes stratified into two groups: the first with complete absence of germ cells [Sertoli cell-only (SCO)] and the second with arrested spermatogenesis (SCA). METHODS: Immunohistochemistry for the T-lymphocyte marker CD3 and cytotoxic markers CD8, TIA-1 and granzyme B was performed on paraffin-embedded sections. RESULTS: The number of CD8+ and CD3+ intra-epithelial lymphocytes (IELs) increased distally throughout the normal epididymis. TIA-1 immunostaining revealed that a significant proportion of IELs exhibited cytotoxic potential, whereas granzyme B staining disclosed a subpopulation of activated cytotoxic lymphocytes (CTLs). TIA-1/CD8 and granzyme B/CD8 double immunostaining revealed that the vast majority of TIA-1+ and granzyme B+ cells were CD8+. The proportion of activated granzyme B+ lymphocytes increased distally throughout the normal epididymis. The number of TIA-1+ and granzyme B+ intra-epithelial and stromal lymphocytes was significantly increased in the normal as opposed to the SCO cryptorchid epididymis and proximal vas deferens. CONCLUSIONS: These results suggest that exposure of the testicular excurrent ducts to spermatozoa or immature germ cells triggers the activation and recruitment of CTLs. Cytotoxic granule effector mechanisms may contribute to the immunological barrier preventing the immune response to spermatozoa in testicular ducts.