Neuroimmune interactions in the intestine are essential for maintaining tissue homeostasis, yet they remain poorly understood in teleost fish. This study investigated the structural and cellular organization of enteric neurons and immune cells in the intestine of goldfish (Carassius auratus) using semithin histology, transmission electron microscopy (TEM), and confocal immunofluorescence. Histological observations revealed a well-organized epithelium composed of enterocytes and goblet cells, with numerous lymphocytes located in the basal epithelium. Prominent gut-associated lymphoid tissue (GALT) was identified in both scattered and aggregated forms within the lamina propria and submucosa. Macrophages were widely distributed throughout all intestinal layers and were consistently found in close proximity to enteric neurons and nerve fibers. Ultrastructural analysis confirmed direct contacts between macrophages and neuronal elements. These macrophages exhibited typical phagocytic features, including lysosomes, vacuoles, and engulfed material, particularly in association with myenteric nerve fibers. Immunofluorescence analysis revealed strong expression of toll-like receptor 2 (TLR2) and major histocompatibility complex class II (MHC II) in macrophages and enterocytes, suggesting an active role in antigen recognition. Langerin-positive dendritic-like cells were identified in the submucosa, while CD4-positive lymphocytes showed partial colocalization with serotonin (5-HT). S100-positive cells also exhibited partial overlap with 5-HT, and goblet cells demonstrated serotonin immunoreactivity. In addition, inducible nitric oxide synthase (iNOS) colocalized with TLR2 in submucosal immune cells. These findings demonstrate a close structural and functional association between enteric neurons and immune cells, highlighting an integrated neuroimmune network in the goldfish intestine.

The limbus is a specialized region of the ocular surface, but its structural organization in teleosts remains poorly documented. This study provides the first integrated histological, immunohistochemical, and ultrastructural analysis of the goldfish limbus. The limbal epithelium consisted of stratified non-keratinized epithelial cells supported by a markedly undulating basement membrane and prominent epithelial ridges. The underlying stroma contained collagen fibers, fibroblasts, blood vessels, immune cells, melanocytes, and numerous telocytes. CD117 immunoreactivity was detected mainly in scattered basal and parabasal epithelial cells, with occasional positive stromal cells and telocytes, whereas E-cadherin showed strong membranous expression throughout the epithelium. Ultrastructurally, basal epithelial cells exhibited abundant mitochondria, rough endoplasmic reticulum, and vesicles and were connected by numerous desmosomes and membrane interdigitations. Telocytes displayed elongated moniliform telopodes forming an extensive stromal network, while mast cells, macrophages, and lymphocytes were observed within the epithelial compartment. These findings demonstrate that the goldfish limbus is a structurally complex epithelial–stromal region containing diverse cellular populations. The study provides a morphological framework for future investigations into epithelial maintenance, cellular interactions, and regenerative mechanisms at the teleost ocular surface.

The striped dolphin (Stenella coeruleoalba) is a small pelagic dolphin. The melon, present in most odontocetes, is a rounded structure located in the center of the forehead, between the blowhole and the tip of the head. The dolphin's melon, as well as the blubber, consists of a lipid component similar to that of adipose tissue, with large, rounded cells closely related to each other and a muscular component. The melon primarily plays a role in echolocation, but this organ can also be involved in immune function. Numerous studies have demonstrated the accumulation of contaminants, such as heavy metals, in the fatty tissues of cetaceans (melon and blubber), which alter the immune system and stimulate an inflammatory response. This study aims to describe the involvement of Stenella coeruleoalba melon in immune function. Histological samples of the melon of Stenella coeruleoalba, were used in this study. To describe the morphology of this organ, the sections of the tissue were stained with Giemsa, Masson, and Mallory staining techniques. Immunoperoxidase and immunofluorescence techniques using specific antibodies such as MHC II, Langerin/CD 207, TLR2, and CD14 were used to characterize melon immune cells, providing novel insights into their immunological features. The results showed scattered immune cells among melon adipocytes immunoreactive to the tested antibodies; macrophages are the principal immune cells infiltrating adipose tissue, and their function is to secrete proinflammatory mediators. Furthermore, the adipocytes themselves appear to be labeled with the antibodies used. This study demonstrates the involvement of the dolphin melon in immune function, helping us better understand the immune system of cetaceans, which is still little understood. Furthermore, it could also demonstrate that analyses of blubber collected from deceased individuals of highly protected species can provide valuable information on their health status and exposure to contaminants.