What are the CD34(+) cells in benign peripheral nerve sheath tumors? Double immunostaining study of CD34 and S-100 protein

To determine whether CD34 expression in nerve sheath lesions was found in a unique cell population or in a subset of nerve sheath cells, we performed double immunohistochemical staining using a standard avidin-biotin complex method with 2 separate color developing systems. We studied 40 neurofibroma s and 16 neurilemomas. All lesions strongly expressed S-100 in nuclei and c ytoplasm. CD34 was detected in cells having ameboid dendritic cytoplasm pre sent in greatest numbers in Antoni B zones of neurilemomas, myxoid zones of neurofibromas, at the periphery of lobules in both tumor types, and conden sed in apposition to perineurium. The CD34+ cells also were detected in nor mal nerves. They were infrequent in Antoni A zones of neurilemomas. No dual S-100 and CD34 expression was seen. This double immunostaining confirms th e presence of a CD34-reactive non-Schwannian cell type in these neural neop lasms. As the CD34+, S-100-negative cell population is present also in norm al nerves and infrequently seen in the areas of cellular neoplastic Schwann cells, CD34+, S-100-negative cells in peripheral nerve sheath turners most likely are nonneoplastic and may have a supportive function.