The origin of lymphatic capillaries in murine testes

It is known that the seminiferous tubules are bathed in a sea of lymph in mice, which are commonly used in reproductive and immunological studies. Although testicular lymphatic vessels arising from the tunica albuginea can be macroscopically observed in mice, the exact distribution of the lymphatic capillaries remains unclear. In the present study, we investigated the distribution of lymphatic capillaries in normal testes by immunohistochemical staining with monoclonal antibodies against lymph vessel endothelium HA-receptor 1 (LYVE-1) and a platelet endothelial cell adhesion molecule (CD31). Moreover, normal lymphocytes were locally injected into the testes of recipient mice, and their migration was investigated with the use of LYVE-1 and CD31. The results showed that lymphatic capillaries were in and just beneath the tunica albuginea but not in the interstitium between the seminiferous tubules. It was also noted that these were abundant in the thickened tunica albuginea adjacent to the epididymis, but they were scarce in the thin tunica albuginea opposite the epididymis. When normal lymphocytes were locally injected into testes, the injected lymphocytes migrated between the seminiferous tubules and then drained into the lymphatic vessels in the tunica albuginea. These results suggest that tissue fluid might drain from lymphatic capillaries that arise just beneath the tunica albuginea.