Description of epithelial granular cell in catshark spiral intestine: Immunohistochemistry and ultrastructure

We evaluated the histology of the spiral intestine of the blackmouth catshark (Galeus melastomus), a small shark distributed in the eastern Atlantic and Mediterranean Sea basin. Entire digestive tracts of 10 G. melastomus were studied using histochemical, immunohistochemical, and ultrastructural methods. Our studies identified a unique, large granular cell type in the intestinal epithelium. Transmission electron microscopy showed that the epithelial granular cell type made intimate contact, by means of junctional complexes, with adjacent epithelial and mucous cells. Several histochemical staining methods showed that the cytoplasmic granules were strongly eosinophilic. Immunostaining of intestinal sections revealed immunoreactivity of the granular cell to tumor necrosis factor‐α (TNF‐α) antibody. However, no reactivity to inducible‐nitric oxide synthase (i‐NOS), interleukin‐6 (IL‐6), interleukin IL‐1β, lysozyme, serotonin 5‐HT antibodies was detected.