RESEARCH ARTICLE Description of epithelial granular cell in catshark spiral intestine: Immunohistochemistry and ultrastructure Bahram Sayyaf Dezfuli 1 | Maurizio Manera 2 | Giampaolo Bosi 3 | Paolo Merella 4 | Joseph A. DePasquale 5 | Luisa Giari 1 1 Department of Life Sciences and Biotechnology, University of Ferrara, Ferrara, Italy 2 Faculty of Biosciences, Food and Environmental Technologies, University of Teramo, Teramo, Italy 3 Department of Veterinary Sciences and Technologies for Food Safety, Università degli Studi di Milano, Milan, Italy 4 Department of Veterinary Medicine, University of Sassari, Sassari, Italy 5 Morphogenyx Inc, New York, New York Correspondence Bahram Sayyaf Dezfuli, Department of Life Sciences and Biotechnology, University of Ferrara, Borsari St. 46, 44121 Ferrara, Italy. Email: dzb@unife.it Funding information University of Ferrara Abstract We evaluated the histology of the spiral intestine of the blackmouth catshark (Galeus melasto- mus), a small shark distributed in the eastern Atlantic and Mediterranean Sea basin. Entire diges- tive 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. KEYWORDS elasmobranch, gut, histology, tumor necrosis factor-α 1 | INTRODUCTION Recent investigations on fish immune system have greatly expanded our knowledge on evolution and diversification of the vertebrate immune system and generated crucial insights into mammalian immu- nity and immunity in general (Sunyer, 2013). In all gnathostomes, a specific adaptive immune system which relies on T and B cells pro- tects all mucosal surfaces (Cooper & Alder, 2006). B and T cells have evolved specific phenotypes and biological functions which render them suitable to cope with the mucosal antigenic environment (Salinas, 2015). However, the relevant immune functions differ between mammal and other ganthostomes (e.g., jawed fish) as listed in Rauta, Nayak, and Das (2012), briefly, according to above authors, jawed fish have low antibody affinity, mammals have high, jawed fish show slow antibody response whereas, mammals show fast, jawed fish possess weak memory response, as contrary mammals have strong, in jawed fish lymphoid nodes are absent conversely they are present in mammals, finally in jawed fish gut-associated lymphoid tis- sues (GALT) are not organized, but in mammals GALT are organized. Specific mucosal immunoglobulin in teleost (IgT) is analogous to mam- malian IgA, and they are able to develop a specific mucosal immune response against various pathogens (Gomez, Bartholomew, & Sunyer, 2014). Elasmobranchs are a group of Chondrichthyes represented by approximately 500 species of rays and skates and 400 species of sharks (Compagno, 1999). Galeus melastomus is a catshark belonging to the Scyliorhinidae, the largest shark family with at least 15 genera and more than 100 species. Species tend to be small, often less than 1 m. Catsharks and other members of the order Carcharhiniformes make up the majority of sharks in many tropical and warm temperate seas (Compagno, 1984; Nelson, 1994). Galeus melastomus in the Medi- terranean Sea is representative of the genus (Castilho, Freitas, Silva, Fernandez-Carvalho, & Coelho, 2007). An account of its biology and distribution in the Strait of Sicily (Italy) was published in Ragonese et al. (2009). Adult individuals of G. melastomus are frequently traded and consumed in some areas (Abella & Serena, 2005). There are few publications examining the basic range, biology, and distribution of G. melastomus (Bottari et al., 2014; Ragonese et al., Received: 31 August 2018 Revised: 22 October 2018 Accepted: 26 November 2018 DOI: 10.1002/jmor.20932 Journal of Morphology. 2018;1–9. wileyonlinelibrary.com/journal/jmor © 2018 Wiley Periodicals, Inc. 1