Merkel Cells in the Human Fetal and Adult Esophagus

Summary

Merkel cells in the skin and the nearby mucous membranes have been well studied. However, there are still very few data concerning neuroendocrine and Merkel cells in the esophagus. In the present study, we extended these investigations to a larger group of post-mortem whole esophagus specimens. Twenty-five specimens of adult and 25 specimens of fetal esophagus were studied using immunohistochemistry. For evaluation of the immunoprofile and innervation of the Merkel cells, various antibodies were used (against cytokeratins 18, 19, 20, chromogranin A, NSE, synaptophysin, serotonin, neurofilament). For evaluating the distribution of the Merkel cells, antibodies against cytokeratin 20 were decisive. Merkel cells could be detected in 80% of the adult and 68% of the fetal specimens. The number of Merkel cells varied markedly from case to case, reflecting a great interindividual variation. On average, there were 2.2 Merkel cells/cm esophageal mucosa in the adult and 1.2 Merkel cells/cm in the fetal specimen. The adult esophageal Merkel cells occurred as single cells located in the lower parts of the epithelial layer. Most of these Merkel cells did not possess long dendrites. No stromal Merkel cells were detected. Fetal Merkel cells first occurred in the 13th week of gestation. They were often arranged in small clusters, bearing long dendrites and being also located in the upper and uppermost layers of the epithelium. A few stromal fetal Merkel cells were apparent first occurring in the 20th week. The immunoprofile of the Merkel cells was comparable to that of Merkel cells in the human skin. No innervation of the Merkel cells could be detected. Our study supports the fact that Merkel cells exist in the human esophagus. For the first time we were able to document fetal esophageal Merkel cells. A marked interindividual variation in the distribution, and moreover, the sole presence of Merkel cells were striking, provoking some speculation concerning the function of human esophageal Merkel cells, especially as no innervated Merkel cells were found. Further studies on various animals may be helpful to answer the question of whether human esophageal Merkel cells perhaps are a phylogenetic rudiment.