Healthy peripheral nerve tissue. Hematoxylin/Eosin staining shows a bundle of nerve fibers ensheathed by the perineurium and surrounded by fat tissue and further nerve fascicles at 40 × magnification (A). At 400x magnification the structure of the endoneurium (B) is visible. Elastica-van-Gieson staining (C) and silver stain according to Gomori (D) reveal the content of collagen and elastic fibers of the endoneurium. In the peripheral nerve system Schwann cells produce the myelin nerve sheaths; they express S100 (E), Vimentin (F) and at a low level GFAP (G). Axons are visualized by Neurofilament (J) and PGP9.5 (I), and myelinated nerve fibers by MBP (H). Neurofibromin 1 (K) is detectable in the cytoplasm and nuclei of Schwann cells while Neurofibromin 2 is mainly found by immunohistochemistry in the nucleus (L). bar = 50 µm.