Recently, teleost species have been considered important model systems for investigating
different research areas including immunologic one. The available literature
provides poor data about the localization and the structure of pancreas in Molly fish.
Moreover, little attention has been paid to the immunologic role of pancreatic tissue
of teleost, particularly Molly fish; therefore, this study aimed to highlights the description
of pancreatic tissue in Molly fish using light- and electron- microscopy, focusing
on the role of pancreatic immune cells and pancreatic acinar cells in immune
responses. Microscopic analysis revealed that the pancreas of Molly fish was composed
of intrahepatic, disseminated and compact parts. Exocrine pancreatic tissue
was diffusely extended within the hepatic tissue forming hepatopancreas. The disseminated
pancreas appeared as several irregular nodules of pancreatic tissue localized
within the mesenteric adipose tissue. The compact pancreas appeared as an oval
shaped body embedded within the mesenteric adipose tissue between the spleen
and the intestinal loops. Several telocytes and melanomacrophages were detected
within the disseminated pancreatic nodules. Moreover, dendritic cells were found in a
close association to the exocrine pancreatic acini. The pancreatic acinar cells showed
strong immunoreactivity to APG5, TGF-β, IL-1β, NF-κB, Nrf2, and SOX9 in both
hepatopancreas and disseminated pancreas of Molly fish. S100 protein revealed a
strong expression in the exocrine pancreatic acinar cells of disseminated pancreas
and also in the endocrine cells of the compact pancreas. In conclusion, findings of this
study suggest the potential role of the pancreas of the Molly fish in cell proliferation
and differentiation, proinflammatory cytokines stimulation, and regulation of both
innate and adaptive immunity.