Distribution and role of CD34-positive stromal cells and myofibroblasts in human normal testicular stroma.

CD34-positive stromal cells are distributed in various organs including breast, Fallopian tubes, thyroid gland, colon, pancreas, and uterine cervix. To elucidate the distribution of CD34-positive stromal cells, smooth muscle cells, and myofibroblasts in normal human testis, we examined 48 testes obtained by autopsy and operation, including five fetal, one neonatal, and 42 adult cases without evident testicular lesions, using a streptavidin-biotin immunoperoxidase technique. The expression of alpha-smooth muscle actin (ASMA), h-caldesmon, CD34, and CD31 were immunohistochemically examined in all cases. The tunica albuginea and the inner layer of seminiferous tubules in adult testis were predominantly composed of myofibroblasts. Smooth muscle cells were also scattered throughout these sites in some cases. CD34-positive stromal cells were abundant, and they formed a reticular network around the seminiferous tubules and Leydig cells as well as the outer layer of seminiferous tubules. Moreover, myofibroblasts and the CD34 reticular network were already present in the testicular stroma during fetal or neonatal development. Double immunostaining of fetal, neonatal and adult testes using ASMA and CD34 confirmed that myofibroblasts and CD34-positive stromal cells were present in the inner and outer layers of peritubular tissue, respectively. This distribution and cytological identification was also confirmed by an ultrastructural study of four cases. Finally, CD34-positive stromal cells and myofibroblasts are major components of human testicular stroma.