Structural organization of subgemmal neurogenous plaques in foliate papillae of tongue.

Little is known about subgemmal neurogenous plaques in the foliate papillae of tongue, which prompted the present investigation. The plaques were immunohistochemically studied in biopsies from 16 adults with the use of neural, stromal, basement membrane, and cell-cycle markers. They displayed a zonal pattern of organization. The neurofibroma-like superficial zone expanded lamina propria and was contiguous to the epithelium covering the papillae. It consisted of tangled composites of S-100 protein-positive spindled cells and fibrils stained for protein gene product 9.5 and neurofilament protein. The composites also expressed the CD56 antigen, could be traced into overlying taste buds, were associated with abundant laminin, and were intermingled with scattered dendritic cells expressing factor XIIIalpha and with mast cells decorated on staining for CD117. Similar composites, but arranged in fascicles and invested by epithelial membrane antigen-positive and collagen IV-positive sheaths, characterized the deep zone of the plaques. Intrafascicular CD57-positive myelin-like annuli and CD34-positive spindled cells were also features of this zone. The sheaths and, most often, the CD57-positive annuli and CD34-positive cells were progressively spread apart toward the intermediate zone of the plaques and were lost superficially. Ki67 and Bcl-1 were not expressed in the plaques. The results suggest that composites of Schwann cells and unmyelinated axons make up the superficial bulk of the plaques, whereas perineurial cells, endoneurial fibroblasts, and myelinated axons are present more deeply. It is possible that the composites achieve neuroeffector relationships and are not neoplastic. Trophic influences from gustatory nerve fibers could play a role in the development of the plaques.