The innervation of intradermal nevi. On the nevus-axon relations.

In the study of the histogenesis of intradermal nevi, the nevus cell-Schwann cell relationship has been a matter of long debate. We have demonstrated a dense axonal supply in the intradermal nevi by protein gene product 9.5 (PGP 9.5) immunohistochemistry. There were small nerve bundles between nevus cell nests and numerous individual axons in the nests of all the intradermal nevi studied. The distribution of these axons was more dense in the deeper and middle portions than in the superficial portion of the nevi. The significance and morphogenesis of this rich axonal supply in the intradermal nevi remain obscure, but this nevic neurotropism suggests an intimate mutual interaction between nevus cells and axons: possibly, some activities of nevus cells stimulating axonal proliferation, or nevus cell migration into the preexisting nerves. The presence of the proliferated axons may have some influences upon Schwannian transformation of the nevus cells. The mode of contact between nevus cell and axon, the presence of true Schwann cells surrounding the proliferated axons and the demonstration of myelin structure should be investigated by further electron microscopic study.