[Endocrine cells and Malpighian epithelium. Merkel-type cells? Immunohistochemical and ultrastructural study]

This study was devoted to a peculiar population of argyrophilic cells present among various stratified squamous epithelia. The purpose of the study was to determine the distribution and the nature of these argyrophilic cells, and to reappraise their degree of analogy with the Merkel cells of epidermis. Examples of squamous epithelia from skin, exocervix, anal canal and dermoid cyst of ovary were investigated using histochemical, immunohistochemical and ultrastructural techniques. Melanin-containing cells as well as peculiar argyrophilic cells were revealed in each series of specimens. These peculiar argyrophilic cells expressed EMA, chromogranin A and NCL-5D3 (cytokeratins 19, 18, 8) immunoreactivities. By contrast, they were serotonin negative. An intense staining for EMA was observed. These cells were obviously endocrine cells. Ultrastructural studies confirmed the presence of endocrine cells within the anal canal and the exocervix; moreover, in anal canal, some of these cells appeared to have contacts with a nerve terminal. Through the epidermis, these cells can only correspond to Merkel cells, because of their chromogranin positivity. Throughout other squamous epithelia, this population of endocrine cells (serotonin negative) bear some analogies with Merkel cells of epidermis. Their distribution, morphology, EMA immunoreactivity and ultrastructural appearance were reminiscent of those of the Merkel cells. They could be named Merkel-type cells. Additional studies, using other characteristic or specific markers of Merkel cells, are clearly required to determine the exact degree of analogy between these types of cells. Merkel-type cells could be largely distributed through stratified squamous epithelia from various tissues. They can be easily visualized by their strong EMA immunoreactivity and must be distinguished from Paget cells.