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Rodlet cells (RC) are characterized by a distinctive cell cortex and conspicuous inclusions named "rodlets." These cells are particularly abundant and large in size in intestine of eels. Histochemical, immunohistochemical and ultrastructural investigations were carried out on European eel Anguilla anguilla and Common carp Cyprinus carpio from Northern Italy. Eight biotinylated lectins were used to probe for specific carbohydrate residues in deparaffinized, hydrated intestinal sections of eel and carp. Five antibodies were tested on intestinal sections of both fish species: inducible nitric oxide synthase (i-NOS), leu-enkephalin, lysozyme, serotonin and tumour necrosis factor-α. Lectin histochemistry revealed rodlet cells (RCs) of the eel intestine to react with two of the eight lectins tested, specifically Concanavalin A (ConA) and Sambucus Nigra Agglutinin (SNA). This contrasted to lectin staining of RCs in the intestine of common carp, where four of the eight lectins showed a positive reaction; Dolichos Biflorus Agglutinin (DBA), Wheat Germ Agglutinin (WGA), SNA and ConA. RCs in eel and carp intestine were immunoreactive with antibodies to lysozyme and i-NOS. The occurrence of the inflammatory peptides lysozyme and i-NOS in RCs of the eel and common carp poses in favour that these cells are involved in the mechanism of defence against pathogens., (© 2017 John Wiley & Sons Ltd.)

The histopathology and ultrastructure of the intestine of mullets, Liza ramada and Liza saliens, from Comacchio lagoons (northern Italy) naturally infected with myxozoans and helminths were investigated and described. Sixty-two (80.5%) of 77 mullets harboured one or more of the following parasites species: Myxobolus mugchelo (Myxozoa), Neoechinorhynchus agilis (Acanthocephala), Haplosplanchnus pachysomus and Dicrogaster contractus (Digenea). Co-occurrence of helminths with myxozoans was common. The main damage caused by digeneans was destruction of the mucosal epithelium of the villi, necrosis and degeneration of intestinal epithelial cells. More severe intestinal damage was caused by acanthocephalans which reach the submucosa layer with their proboscis. At the site of helminths infection, several mast cells (MCs), rodlet cells (RCs), mucous cells and few neutrophils and macrophages were observed in the epithelium. RCs and mucous cells exhibited discharge activity in close vicinity to the worm's tegument. M. mugchelo conspicuous plasmodia were encysted mainly in muscle and submucosa layers of the intestine. Indeed, spores of M. mugchelo were documented within the epithelial cells of host intestine and in proximity to MCs. Degranulation of the MCs near the myxozoans was very frequent., (© 2017 John Wiley & Sons Ltd.)

Histopathological lesions due to third-larval stage of nematode Brevimulticaecum sp. within the liver of a subpopulation of 31 Gymnotus inaequilabiatus from the Pantanal Region (Brazil) were studied with histochemical and immunohistochemical methods. In 93.5% of fish, livers harboured nematode larvae and the intensity of infection ranged from 8 to 293. In livers with highest number of larvae, the hepatic tissue was occupied primarily by the nematodes. Each larva was encircled by focal inflammatory granulomatous reaction. Within the thickness of the granuloma, three concentric layers were recognized: an inner layer of densely packed epithelioid cells, a middle layer of mast cells (MCs) entrapped in a thin fibroblast-connective mesh and an outer layer of fibrous connective tissue with fibroblasts. Epithelioid cells and fibroblasts within the thickness of the granuloma wall were positive for proliferative cell nuclear antigen (PCNA). Moreover, several hepatocytes in infected liver were immunoreactive to PCNA. Occurrence of rodlet cells and MCs in parenchyma, in close proximity to the encysted nematode larvae and near the blood vessel of infected liver, was observed. Macrophage aggregates (MAs) were numerous within the granulomas and scattered in parenchyma of the infected liver. High quantity of haemosiderin was encountered in MAs and hepatocytes of infected liver., (© 2017 John Wiley & Sons Ltd.)

Histopathological, immunofluorescence and ultrastructural studies were conducted on the intestines of four fish species infected with different taxa of enteric helminths. Brown trout (Salmo trutta trutta), eel (Anguilla anguilla) and tench (Tinca tinca) obtained from Lake Piediluco (central Italy) were examined. Brown trout and eel were infected with two species of acanthocephalans, and tench was parasitized with a tapeworm species. In addition to the above site, specimens of chub (Squalius cephalus) and brown trout infected with an acanthocephalan were examined from the River Brenta (north Italy). Moreover, eels were examined from a brackish water, Comacchio lagoons (north Italy), where one digenean species was the predominant enteric worm. All the helminths species induced a similar response, the hyperplasia of the intestinal mucous cells, particularly of those secreting acid mucins. Local endocrine signals seemed to affect the production and secretion of mucus in the parasitized fish, as worms often were surrounded by an adherent mucus layer or blanket. This is the first quantitative report of enteric worm effects on the density of various mucous cell types and on the mucus composition in intestine of infected/uninfected conspecifics. We provide a global comparison between the several fish-helminth systems examined., (© 2016 John Wiley & Sons Ltd.)

The European eel, Anguilla anguilla, is a major warm-water fish species cultured in North and South Europe. Seventy-one A. anguilla collected between 2010 and 2015 from the Comacchio lagoons were examined. Fish were infected and damaged by larvae (L3) of the nematode Contracaecum rudolphii A, which were encapsulated within the thickness of the intestinal wall and within the external visceral peritoneum (serosa). Conspicuous granulomas, visible at sites of infection, were arranged in a trilayer, formed by a series of concentric whorls. The cells involved in the immune response and their distribution in the granuloma layers were assessed by immunohistochemical, immunofluorescence, and ultrastructural techniques. The outer part of the granuloma contained macrophages, macrophage aggregates, and mast cells (MCs) scattered among fibroblasts. This layer was vascularized, with degranulation of MCs occurring in close proximity to the capillaries. The middle layer was rich in MCs and fibroblasts. The inner layer, closest to the parasite larva, consisted mainly of dark epithelioid cells, some of which were necrotic. Non-necrotic epithelioid cells formed desmosomes between themselves or with fibroblasts. Within the granulomas, numerous cells of different types were positive to proliferative cell nuclear antigen antibody, indicating a high degree of cellular proliferation around the larvae., (© 2016 John Wiley & Sons Ltd.)

Histochemical and ultrastructural investigations were conducted on the mucous cells of the intestine of brown trout, Salmo trutta L., naturally infected with the cestode Cyathocephalus truncatus (Pallas, 1781) and the acanthocephalan Echinorhynchus truttae Shrank, 1788. A subpopulation of 45 S. trutta were examined of which 15 specimens harboured E. truttae, 15 of which were infected with C. truncatus and 15 fish, the control group, were uninfected. In histological sections, hyperplasia and hypertrophy of the mucous cells were evident at the site of parasite infection. Enhanced mucus secretion was also recorded in infected fish. The number of mucous cells close to the site of parasite attachment within the intestine was significantly higher than the number detected in uninfected individuals and in infected individuals at sites 1 cm or greater from the point of parasite attachment. There were no significant differences between the number of mucous cells found at the latter two sites. Alcian blue and periodic acid-Schiff's staining of representative histological sections revealed a significant increase in the number of mucous cells staining positively for acid glycoconjugates compared to the number of cells found in the intestines of uninfected S. trutta. In transmission electron microscopy sections, each mucous cell typically possessed an elongated, basally positioned nucleus. The cytoplasm was observed to possess numerous electron dense and lucent vesicles, in addition to well-developed rough endoplasmic reticulum, Golgi apparatus and a few round mitochondria.

Immunopathological and ultrastructural studies were carried out on the gills of bream, Abramis brama, naturally infected with the copepod Ergasilus sieboldi and on the intestine of brown trout, Salmo trutta, infected with the acanthocephalan Echinorhynchus truttae. Infected gills showed extensive tissue damage due to copepod attachment, including hyperplasia, as well as proliferation of mast cells, rodlet cells and mucous cells. In parasitized gills of bream, mast cells were more abundant than in uninfected gills. They were free within the lacunae, as well as outside and inside the blood vessels of the primary lamellae, and made intimate contact with vascular endothelial cells and with neutrophils. In some infected gills, degranulation of mast cells was common. Infected intestines of brown trout had more mast cells than uninfected intestines, and these cells were often in close proximity to, and inside, the capillaries and lying close to fibroblasts of the muscularis layer and stratum granulosum. Intense degranulation of mast cells was encountered in all intestinal layers, especially near the E. truttae body.

The pathological changes induced by an infection of Diphyllobothrium dendriticum (Nitzsch, 1824) plerocercoids in powan, Coregonus lavaretus (L.), from Loch Lomond, Scotland, were assessed using immunohistochemical and ultrastructural techniques. In a sample of 26 powan, the occurrence of encysted plerocercoids of D. dendriticum on the outer surface of the stomach was 38.5% (n = 10) with the number of cysts ranging from 4 to 15 and measuring 4.2 +/- 1.0 mm x 3.4 +/- 0.9 mm (mean +/- SD). Histological examination of intestinal samples also revealed plerocercoids (2-21) encapsulated within a proliferation of mesenteric fibrous tissues of the gastric wall and, occasionally, by the gut lamina propria-submucosa and lamina muscularis. In section, cysts were tri-layered and were formed from a series of concentric whorls of fibroblast and collagen fibre-based connective elements. The extent of necrosis within each muscle layer and the serosa of the stomach differed, notably within the latter that was marked by a chronic inflammatory reaction and fibrosis. Within the cyst and around it, a large number of degranulating mast cell/eosinophilic granule cells were seen, in addition to melano-macrophage centres. Immunohistochemical staining of sections of infected stomach revealed a high density of elements, in close proximity to plerocercoids, staining positive for serotonin, bombesin, substance P and galanin. Uninfected material did not present the same levels of activity. Sections through both infected and uninfected tissue were also tested for elements containing vasoactive intestinal peptide, met-enkephalin, calcitonin gene-related peptide, neuropeptide Y and nitric oxide synthase, but these were absent.

A histopathological and immunohistochemical study on the intestines of 45 specimens of farmed rainbow trout, Oncorhynchus mykiss (Walbaum), from Loch Awe, Scotland, revealed a number of cellular deviations in individuals naturally infected with the pseudophyllidean cestode Eubothrium crassum (Bloch, 1779). Twenty-five individuals (55.5%) were infected with an average worm burden of 18.84 +/- 4.06 (mean +/- SE) cestodes per host (range, 2-80 worms; total 471 worms). The cestodes, measuring an average 8.23 +/- 1.10 cm (mean +/- SE; range, 5.3-13.0 cm) in length, were found attached by their scolices to the mucosal lining of the distal portion of the pyloric caeca. Within the caeca, the strobila evoked a mild catarrhal enteritis, namely an enhanced mucus production with epithelial cellular desquamation, a leucocytic infiltration of the lamina propria-submucosa and vacuolization of the intestinal epithelial cells. Eosinophilic granular cells of the stratum granulosum exhibited granular depletion, while within the catarrh, the presence of a high number of rodlet cells was noticed. Immunohistochemically, the occurrence of E. crassum caused a significant reduction in the number of bombesin-, gastrin-releasing peptide and glucagon-like immunoreactive endocrine cells, but an increase in the relative densities of endocrine cells containing cholecystokinin-8- and gastrin-like substances. There were, however, no significant differences in the number of endocrine cells that were immunoreactive to secretin, neuropeptide Y and peptide histidine-isoleucine antisera in the digestive tracts of either the infected or non-infected O. mykiss.

The presence of intestinal helminths in the alimentary canal of brown trout, Salmo trutta L., can alter the number of cells that synthesize modulatory peptides. A total of 167 brown trout were collected from tributaries of the River Brenta (northern Italy), of which 119 (71.3%) specimens were infected with enteric helminths, 28 with the acanthocephalan Pomphorhynchus laevis Müller, 1776 with intensity of infection ranging from 1 to 162 (18.57 +/- 30.79) worms per host and 67 fish with the cestode Cyathocephalus truncatus Pallas, 1781. Intensity of infection with C. truncatus ranged from 1 to 85 (6.87 +/- 12.59) per fish. In 24 fish there were concurrent infections of both species of helminths. The caecal and middle regions of the intestine were the most heavily parasitized. Immunohistochemical tests showed a decrease in endocrine cells (ECs) of the diffuse endocrine system (DES) positive to gastrin, cholecystokinin-8, bombesin and secretin antisera in the intestine of the infected trout. The number of ECs immunoreactive to anti-glucagon serum did not show differences in the digestive tract of uninfected brown trout and in conspecifics parasitized with P. laevis. The density of cells containing glucagon-like material was low in the fish parasitized with C. truncatus. The results suggest that endoparasitic helminths induce alterations in the DES of infected S. trutta.