Detecting Intestinal Goblet Cells of the Broadgilled Hagfish Eptatretus cirrhatus (Forster, 1801): A Confocal Microscopy Evaluation

SIMPLE SUMMARY: The intestinal epithelium of fish, similar to mammals, consists mainly of enterocytes and goblet cells. Goblet cells play a key role in the secretion of mucus, which, in addition to promoting the digestion of nutrients, is the first protective barrier against bacteria, viruses, and pathogens. Our study aims to evaluate the presence, localization, and co-localization of 5-HT, TLR2, iNOS, and Piscidin1 in goblet cells of the intestine of Eptatretus cirrhatus. The results obtained by confocal microscopy show, for the first time, the positivity of goblet cells to the antibodies tested, suggesting the involvement of these cells in the intestinal immunity of broadgilled hagfish. ABSTRACT: The fish intestine operates as a complicated interface between the organism and the environment, providing biological and mechanical protections as a result of a viscous layer of mucus released by goblet cells, which serves as a barrier against bacteria, viruses, and other pathogens, and contributes to the functions of the immune system. Therefore, goblet cells have a role in preserving the health of the body by secreting mucus and acting as sentinels. The ancient jawless fish broadgilled hagfish (Eptatretus cirrhatus, Forster, 1801) has a very basic digestive system because it lacks a stomach. By examining the presence, localization, and co-localization of 5-HT, TLR2, iNOS, and Piscidin1, this study intends to provide insight into the potential immune system contributions arranged by the gut goblet cells of broadgilled hagfish. Our results characterize intestinal goblet cells of broadgilled hagfish, for the first time, with the former antibodies, suggesting the hypothesis of conservation of the roles played by these cells also in primitive vertebrates. Moreover, this study deepens the knowledge about the still little-known immune system of hagfish.