S-100 PROTEIN-IMMUNOREACTIVE CELLS IN THE LAMINA PROPRIA AND CARCINOID TUMORS OF THE APPENDIX

Abstract

Appendiceal mucosa and carcinoid tumors were examined immunohistochemically by the immunoperoxidase method for S-100 protein. Light microscopic examination of serial sections showed sparse extraepithelial subglandular argyrophilic cells surrounded by S-100 protein-positive cells within the lamina propria of normal or slightly inflamed appendices. These pairs of cells closely resembled the ultrastructurally defined enterochromafiin cell-nerve fiber (ECC-NF) complexes in their location and topographical relationship, as well as in their cytological and biochemical properties. All four carcinoid tumors examined contained stellate cells giving a strong reaction for S-100 protein. In three tumors, these immunoreactive cells with long cytoplasmic processes were observed at the margin of tumor nests. They often enveloped smaller tumor nests. Conventional electron microscopy showed that the tumor nests were composed of neurosecretory cells containing enterochromaffin granules and polyaxonal unmyelinated Schwann cells located at the periphery of the nests. Electron immunoperoxidase staining for S-100 protein revealed that these immunoreactive cells were identifiable as Schwann cells. These findings show an intimate relation between appendiceal carcinoid tumors and nerve fibers, and suggest that these tumors develop from ECC-NF complexes.