The contribution of RNA-binding motif (RBM) antibody to the histopathologic evaluation of testicular biopsies from infertile men

Testicular biopsies of infertile men are often characterized by mixed histologic patterns, with different types of spermatogenic impairments being found in adjacent seminiferous tubules. RNA-binding motif (RBM) is a nuclear protein expressed exclusively in the male germ cell line. We reasoned that RBM might be a useful marker to identify germ cells in testicular sections, particularly in biopsies with mixed histologic phenotype and small focal concentrations of spermatogenesis. Testicular biopsies from azoospermic men were immunohistochemically evaluated for RBM expression. RBM expression was detectable in spermatogonia, spermatocytes, and round spermatids in biopsies of men with obstructive azoospermia and normal spermatogenesis. No specific cell staining was shown in cases of Sertoli-cell-only (SCO) syndrome. In biopsies of patients with spermatogenic disorders, all the germ cells were stained up to and including the stage level of the arrest in spermatogenesis. This approach enabled identification of small focal concentrations of spermatogenesis in a biopsy previously classified as being SCO by hematoxylin and eosin staining. Thus, RBM can be a useful immunohistochemical marker for the specific identification of germ cells and provide greater accuracy in the histopathologic evaluation of testicular biopsies.