A study of the so-called neurotization of nevi.

Fourteen nevi with neuroid zones were examined and compared with nine nevi without neuroid structures. At light microscopic level, nevus cells from the neuroid nevi and the control nevi show the same staining pattern with polyclonal antibodies against S-100 protein. Around the cells of the neuroid zones is a more intensive immunoreactivity with monoclonal antibodies against laminin and collagen type IV than around the nevus cells in the upper dermis and the nevus cells in the control nevi. Also, the Gordon-Sweet stain for reticulin shows a dense network around the cells of the neuroid zones. No immunoreactivity in the neuroid zones was found with monoclonal antibodies against myelin-basic protein, myelin-associated protein, and glial fibrillary acidic protein. At the electron microscopic level, nevus cells from the neuroid zones show stacks of elongated cytoplasmic processes surrounded by basal lamina material. This pattern explains the presence of the abundant cytoplasm seen at light microscopy. Because no features of neural or neurolemmal differentiation could be found, the exactitude of the term neurotization can be questioned.