Cellular evidence of mucus cell immunological and differentiation characteristics in allogeneic crucian carp intestinal lamina propria

The allogeneic crucian carp is an important fish farm animal with a very different digestive system structure from that of mammals. The lamina propria of the fish intestine is also considered to be an important site of intestinal immunity in fish, but functional histological studies of the lamina propria of the allogeneic crucian carp intestine are still lacking. In this study, Identification of the ubiquitous lamina propria mucus cells in the lamina propria of the intestine by hematoxylin-eosin staining, and determination of the mucocytic properties, class, and distribution of these cells in each intestinal segment by Alcian Blue-Periodic Acid-Schiff (AB-PAS) staining. The results show that type III mucus cells were abundant in the lamina propria of the foregut and midgut, while type II and type IV mucus cells predominate in the hindgut, possibly reflecting the distinct functions of these intestinal segments. Transmission electron microscopy dissected the differentiation of mucus cells in the lamina propria of the intestine at the ultrastructural level and investigated their morphology and distribution patterns in different intestinal segments, the findings revealed that lamina propria mucus cells perform rudimentary functions such as mucous secretion, phagocytosis, and degradation functions. Moreover, immunohistochemistry labeling with CD68 and LAMP1 revealed that numerous cells in the anterior, middle, and posterior intestines were positive for both proteins. Immunofluorescence double-labeling demonstrated that these cells highly co-expressed CD68 and LAMP1. Besides, the distribution and morphology of CD68+ and LAMP1+ cells were similar to those of AB-PAS positive cells and they accounted for the majority of parenchyma cells. Considering the above results, there were abundant cells with both mucous secretion and phagocytosis in the intestinal lamina propria of allogeneic crucian carp, which are a essential component of the intestinal immune process of allogeneic crucian carp. •The lamina propria of each intestinal segment of the allogeneic crucian carp contains a variety of mucus cells different from goblet cells.•The mucus cells in the foregut and midgut of allogeneic crucian carp have neutral mucopolysaccharides, while the hindgut has more acidic mucopolysaccharides.•Mucus cells in all intestinal segments secrete mucus and perform primary degradation functions, with increasing differentiation from the foregut to the hindgut.•The lamina propria mucus c