Differential changes in CD4+ and CD8+ effector and regulatory T lymphocyte subsets in the testis of rats undergoing autoimmune orchitis

Experimental autoimmune orchitis (EAO) is a useful model to study organ-specific autoimmunity and chronic testicular inflammation. EAO is characterized by an interstitial lymphomononuclear cell infiltration and damage of the seminiferous tubules showing germ cell sloughing and apoptosis. Using flow cytometry, we analysed the phenotype and number of T lymphocytes present in the testicular interstitium of rats during EAO development. A large increase in the number of testicular CD3+ T lymphocytes was detected. The number of CD4+ and CD8+ effector T lymphocytes (Teffector cells) dramatically increased in the testis at EAO onset, with the CD4+ cell subset predominating. As the severity of the disease progressed, CD4+ Teffector cells declined in number while the CD8+ Teffector cell subset remained unchanged, suggesting their involvement in maintenance of the chronic phase of EAO. As a novel finding, we detected by immunohistochemistry and flow cytometry Foxp3 expressing CD4+ and CD8+ regulatory T lymphocytes (Tregs) in chronically inflamed testis of EAO rats. The numbers of both Treg cell subsets increased in the testis of rats with orchitis, mainly at the onset of EAO; CD4+Foxp3+ Treg cells were more abundant than CD8+Foxp3+ Treg cells. Unexpectedly, CD25− T lymphocytes were more abundant than CD25+ cells within CD4+Foxp3+ and CD8+Foxp3+ Treg cell populations. Although Treg subsets are actively accumulated into the testis in EAO rats, these cells are outnumbered by an even more vigorously expanding Teffector subset. Further, it is possible that factors present in the inflamed testis might limit the ability of Tregs to abrogate tissue damage.