Methods: The plaques were immunohistochemically studied in biopsies from 16 adults with the use of neural, stromal, basement membrane and cell cycle markers.
Results: The plaques displayed a zonal pattern of organization. The neurofibroma-like superficial zone expanded lamina propria and was contiguous to the epithelium covering lingual folia; it consisted of tangled composites of S-100 protein positive spindled cells and fibrils stained for PGP 9.5 and neurofilament protein. The composites also expressed the CD56 antigen, could be traced into overlying taste buds, were associated with copious laminin, and were intermingled with scattered dendritic cells expressing factor XIIIa and mast cells decorated on staining for CD117. Similar composites, but in fascicular arrangement and invested by epithelial membrane antigen positive and collagen IV positive sheaths, characterized the stem-like deep zone of the plaques; intrafascicular CD57 positive myelin sheaths and CD34 positive spindled cells were also features of this zone. The various sheaths and the CD34 positive cells were progressively spread apart towards the intermediate zone of the plaques, and were eventually lost superficially. Immunostaining for Ki67 and Bcl-1 was uniformly negative throughout the plaque and there were only a few cytokeratin 7 positive neurosensory cells arranged as individual units in the covering epithelium.
Conclusions: The results suggest that composites of Schwann cells and nonmyelinated axons comprise most of the subgemmal neurogenous plaques, whereas perineurial cells, endoneurial fibroblasts and myelinated axons are present to their base. Possibly the composites achieve neuroeffector relationships and are not tumorous. Trophic influences from gustatory nerve fibres could play a role in the development of the plaques.