- The levels of IL-1α, IL-1β and IL-1Ra were higher in homogenates of testicular tissue from sexually immature than those from mature mice. Immunohistochemical staining of testicular tissues from sexually immature and adult mice show that differentiated germ cells express higher levels of IL-1α compared to Sertoli cells and Leydig cells/interstitial cells. Peritubular cells of sexually immature and adult mice did not express IL-1α. Testicular tissue cells of adult mice showed high levels of expression of IL-1β, mainly in the cytoplasm and nucleus of the spermatogonia and in spermatocytes. Sertoli cells and Leydig/interstitial cells were also highly stained for IL-1β. However, peritubular cells did not express IL-1β. On the other hand, testicular tissue cells from sexually immature mice, showed high levels of IL-1β, mainly in spermatocytes. Spermatogonia showed low levels of IL-1β expression. Also, high levels of IL-1β expression were detected in Leydig/interstitial cells. Peritubular cells clearly showed IL-1β expression. Testicular tissue cells from adult mice, showed IL-1Ra expression in spermatogonia, Sertoli and Leydig/interstitial cells. IL-1Ra expression was clearly present in the Golgi apparatus of spermatogonia and Sertoli cells. However, peritubular cells did not show IL-1Ra expression. Testicular tissue cells from sexually immature mice, also showed high levels of IL-1Ra expression mainly in the cytoplasm and nucleus of the spermatogonia and Sertoli cells. In addition, Leydig/interstitial cells and peritubular cells also expressed IL-1Ra. Our results demonstrate, for the first time, the expression of IL-1β in germ and Sertoli cells, and IL-1Ra in Leydig/interstitial cells of testicular tissues from adult and sexually immature mice, under in vivo conditions. In addition, the relative elevated levels of the IL-1 system in the testis of immature mice compared to mature mice may indicate its involvement in the spermatogenesis.