Dual presence of chromogranin A-like immunoreactivity in a population of endocrine-like cells and in nerve fibers in the human anal canal

Abstract

Light microscopic immunohistochemistry was used to investigate the presence and distribution of chromogranin A-like immunoreactivity in the human anal canal. In the anal transitional zone (ATZ), anal duct and anal gland epithelium, a varied number of mostly elongated cells strongly stained for CGA, using an antibody directed to a highly species-conserved region of the CGA molecule or the monoclonal antibody LK2H10. The density of CGA-immunoreactive (ir) cells strikingly increased from the ATZ epithelium towards the anal gland epithelium. CGA-ir cells possessed single processes running perpendicularly to reach the epithelial surface and exhibited basal ramifications that extended parallel to the basal lamina. The number of CGA-ir cells in anal glands exceeded CGA-ir cells in the crypt-bearing colorecal-type mucosa. The abundant population of CGA-ir cells in the anal canal most likely represents a population of specialized endocrine or paracrine cells. CGA-like immunoreactivity was also present in anocutaneous Merkel cells. A sparse number of vascular and non-vascular CGA-ir varicose nerve fibers was present throughout the layers and rostrocaudal divisions of the anal canal and in the perianal skin. Proposed functions of CGA in neuroendocrine cells and nerves of the anal canal include calcium binding and regulation, secretory granule matrix formation, and generation of bioactive peptides.