Testicular autoimmunity

Although the testis is an immunoprivileged organ, infection and inflammation may overwhelm immunosuppressor mechanisms inducing autoimmune reactions against spermatic antigens which result in aspermatogenesis and infertility. Autoimmune orchitis is a model of chronic inflammation useful for elucidating pathogenic mechanisms involved in testicular damage. We developed experimental autoimmune orchitis (EAO) in rats by active immunization with spermatic antigens and adjuvants characterized by interstitial inflammatory cell infiltrate, apoptosis and sloughing of germ cells. Quantitative and phenotypic analysis of testis-infiltrating cells revealed an increased number of macrophages, dendritic cells and T cell subsets that include effector Th1 and Th17 cells as well as Foxp3+ regulatory T cells (Tregs). Immune cells secrete pro-inflammatory cytokines, TNF-α, IFN-γ, IL-6, IL-12, IL-17 and IL-23, which disrupt the normal testicular immunosuppressor microenvironment. As a consequence, increased numbers of germ cells expressing TNFR1, IL-6R and Fas undergo apoptosis. Functional analysis shows that dendritic cells in EAO testis have a mature immunogenic status and are able to induce immune responses to testicular antigens. We also observed that Tregs accumulated in the inflamed testis are functionally suppressive but are unable to downregulate inflammation, probably due to the function limiting effect of pro-inflammatory cytokines.