A comparison of teleost rodlet cells with apicomplexan cells.

Rodlet cells are unique pear-shaped cells found primarily in the epithelium of the teleost fishes. The rodlet cell was first identified by Thèlohan in 1892 who named it Rhabdospora thelohani as it was believed to be a protozoan parasite of the phylum Apicomplexa. The rodlet cell as parasite paradigm persisted for several decades afterwards but has since faded in the last 20 years or so. The rodlet cell is now generally believed to be an immune cell, functioning as an early responder to parasite intrusion. This short review makes a detailed comparison of apicomplexan structure and behavior with that of the rodlet cell to further strengthen the argument against a parasitic nature for the fish cell. It is then proposed that apical microvilli of the rodlet cell serve as a mechanical trigger for rodlet discharge as possible defense against larger ectoparasites.

Differential mucins secretion by intestinal mucous cells of Chelon ramada in response to an enteric helminth Neoechinorhynchus agilis (Acanthocephala).

Intestinal mucous cells produce and secrete mucins which hydrate, lubricate and protect the intestinal epithelium from mechanical injuries due to the transition of digesta or action of pathogens. Intestinal mucous cells are considered elements of the innate immune system as they secrete lectins, toxins, immunoglobulins, and anti-microbial peptides. Acid mucins can surround and eliminate many pathogenic microorganisms. We performed a quantitative analysis of the density and mucus composition of different intestinal mucous cell types from mullet (Chelon ramada) that were infected solely with Neoechinorhynchus agilis. Most N. agilis were encountered in the middle region of the intestine. Mucous cell types were identified with Alcian Blue (pH2.5) and Periodic acid-Schiff (PAS) histochemistry, and by staining with a panel of seven lectins. Mucus enriched for high viscosity acid mucins was accumulated near points of worm attachment. Parasites were surrounded by an adherent mucus layer or blanket. Ultrastructural examination showed intestinal mucous cells typically possessed an elongated, basally positioned nucleus and numerous electron dense and lucent vesicles in the cytoplasm. The results show both an increase in mucus production and changes in mucin composition in infected mullet in comparison with uninfected conspecifics.

Perfluorooctanoic Acid Exposure Assessment on Common Carp Liver through Image and Ultrastructural Investigation.

Perfluorooctanoic acid (PFOA) poses particular concern as an emerging pollutant in both surface and ground waters. Fish, as a natural inhabitant of these waters and being highly representative of vertebrates, represents an ideal animal model to assess the toxic effects of PFOA. Hereby, liver microscopic texture was comparatively evaluated in individuals of common carp subchronically exposed to PFOA using grayscale differential box counting, a fractal analysis method. Furthermore, liver cytoplasmic glycogen areas and ultrastructure were also evaluated and compared to the image analysis findings. Redundancy Analysis was performed to assess, in summary, how much the variation of fractal dimension and lacunarity was explained by the concentration of PFOA in liver, the mass of liver and the number of proliferating cell nuclear antigen (PCNA)-immunoreactive nuclei. Treatment group ordination was better determined by fractal dimension than lacunarity. Interestingly, a significant complexity increase was associated with the modification of liver microscopic texture due to PFOA exposure. This complexity increase was related to "cloudy swelling", possibly representing a primarily adaptive strategy against PFOA challenge, rather than a slight, reversible form of degeneration as traditionally proposed. The occurrence of endoplasmic reticulum stress, unfolded protein reaction and hormetic response was proposed and discussed.

Description of epithelial granular cell in catshark spiral intestine: Immunohistochemistry and ultrastructure.

We evaluated the histology of the spiral intestine of the blackmouth catshark (Galeus melastomus), a small shark distributed in the eastern Atlantic and Mediterranean Sea basin. Entire digestive tracts of 10 G. melastomus were studied using histochemical, immunohistochemical, and ultrastructural methods. Our studies identified a unique, large granular cell type in the intestinal epithelium. Transmission electron microscopy showed that the epithelial granular cell type made intimate contact, by means of junctional complexes, with adjacent epithelial and mucous cells. Several histochemical staining methods showed that the cytoplasmic granules were strongly eosinophilic. Immunostaining of intestinal sections revealed immunoreactivity of the granular cell to tumor necrosis factor-α (TNF-α) antibody. However, no reactivity to inducible-nitric oxide synthase (i-NOS), interleukin-6 (IL-6), interleukin IL-1ß, lysozyme, serotonin 5-HT antibodies was detected.

Actin Microridges.

Microridges are highly distinctive "fingerprint"-patterned structures situated on the outer surface of superficial layer cells of the epithelium. An F-actin-based cytoskeleton is the underlying core structural component of microridges. The basis for much of what is known about microridges has been provided by in vivo and in vitro fish epithelial systems. Nonetheless the microridge literature is quite small, especially when compared with other actin-based cellular structures such as those involved in cell motility. A PubMed search of the terms "Microridges" yields 261 citations from the mid-1970s to the writing of this review. "Microplicae," an alternative name for microridges, and "Actin Microridges" search terms give 204 and 8 references, respectively, in the same time period. By comparison a search of "Lamellipodia" over the same time period yields over 6,400 citations for this important motility structure while a search of the associated "filopodia" results in close to 7,300 articles. Despite the near-ubiquity of microridges in epithelia across species the study of these structures has clearly been neglected. In-depth analysis of microridge molecular composition is very limited while their function remains unclear. This review draws upon information derived from studies of fish as well as mammalian species to provide a more comprehensive view of these structures. The wide-spread distribution of these structures between species and various tissues indicate the microridges have important and common functions in healthy organisms. Conversely, disease conditions may show alterations in microridge structure and function and thus warrant further investigation. Anat Rec, 301:2037-2050, 2018. © 2018 Wiley Periodicals, Inc.

Pigmented macrophages and related aggregates in the spleen of european sea bass dosed with heavy metals: Ultrastructure and explorative morphometric analysis.

The ultrastructure and morphometrics of pigmented macrophages (PMs) were assessed in the spleen of European sea bass experimentally dosed with Cd and Hg. PMs occurred either as solitary cells or as variably structured aggregations, defined as macrophage aggregates (MAs). Light microscopy revealed a high degree of morphological heterogeneity amongst MAs of all experimental groups. At the ultrastructural level, MAs showed a heterogeneous pigment content that was not influenced by the treatment. Cytoplasm rarefaction/vacuolation and euchromatic nuclei, were observed in PMs of dosed fish. Undosed and Cd-dosed samples differ significantly with regard to the following morphometric features: the Minor axis of the best fitting ellipse, Aspect Ratio, and Roundness. In Cd-dosed fish, MAs showed reduced size and complexity. Lacunarity showed significant differences between undosed and both Cd and Hg-dosed samples. These results suggest that heavy metals, and especially Cd, may influence the dynamics of PM aggregation/disaggregation. Variability in splenic MAs was observed both by light and electron microscopy. However, only the morphometric techniques adequately and objectively described the phenomenon, allowing a quantitative/statistical comparison of morphology among experimental groups. These morphometric analyses could be usefully applied in toxicological and ecotoxicological, as well as morpho-functional studies.

Nematode infection in liver of the fish Gymnotus inaequilabiatus (Gymnotiformes: Gymnotidae) from the Pantanal Region in Brazil: pathobiology and inflammatory response.

BACKGROUND: A survey on endoparasitic helminths from freshwater fishes in the Pantanal Region (Mato Grosso do Sul, Brazil) revealed the occurrence of third-larval stage of the nematode Brevimulticaecum sp. (Heterocheilidae) in most organs of Gymnotus inaequilabiatus (Gymnotidae) also known by the local name tuvira. The aim of the present study was to examine Brevimulticaecum sp.-infected tuvira liver at the ultrastructural level and clarify the nature of granulomas and the cellular elements involved in the immune response to nematode larvae. METHODS: Thirty-eight adult specimens of tuvira from Porto Morrinho, were acquired in January and March 2016. Infected and uninfected liver tissues were fixed and prepared for histological and ultrastructure investigations. RESULTS: The prevalence of infection of tuvira liver by the nematode larvae was 95 %, with an intensity of infection ranging from 4 to 343 larvae (mean ± SD: 55.31 ± 73.94 larvae per liver). In livers with high numbers of nematode larvae, almost entire hepatic tissue was occupied by the parasites. Hepatocytes showed slight to mild degenerative changes and accumulation of pigments. Parasite larvae were surrounded by round to oval granulomas, the result of focal host tissue response to the infection. Each granuloma was typically formed by three concentric layers: an outer layer of fibrous connective tissue with thin elongated fibroblasts; a middle layer of mast cells entrapped in a thin fibroblast-connective mesh; and an inner layer of densely packed epithelioid cells, displaying numerous desmosomes between each other. Numerous macrophage aggregates occurred in the granulomas and in the parenchyma. CONCLUSIONS: Our results in tuvira showed that the larvae were efficiently sequestered within the granulomas, most of the inflammatory components were confined within the thickness of the granuloma, and the parenchyma was relatively free of immune cells and without fibrosis. Presumably this focal encapsulation of the parasites permits uninfected portions of liver to maintain its functions and allows the survival of the host.

Multivariate approach to gill pathology in European sea bass after experimental exposure to cadmium and terbuthylazine.

The combined use of guided quantitative expert analysis and of multivariate exploratory data analysis is reported as a robust, sensitive and sufficiently specific approach to study European sea bass gill secondary lamellar pathology after exposure to incremental doses of cadmium and terbuthylazine up to 48h. The following elementary pathological findings were considered: "epithelial lifting", "epithelial shrinkage", "epithelial swelling", "pillar cells coarctation", "pillar cells detachment", "channels fusion", "chloride cells swelling", and "chloride cells invasion". The relative spatial extension was determined according to exposure class and data were analyzed by means of canonical correspondence analysis (CCA), linear discriminant analysis (LDA) and canonical variates analysis (CVA). Histologically and ultrastructurally, cellular shrinkage/coarctation prevailed in cadmium exposed lamellae, whereas cellular swelling and epithelial lifting were predominant in terbuthylazine exposed lamellae compared to unexposed fish. Both CCA and CVA permit a good graphical data grouping according to exposure classes by means of the convex hull minimum polygons. This also reveals exposure dose and time gradients in CCA plot. Accordingly, epithelial swelling and epithelial shrinkage were comparatively associated to higher exposure time, whereas epithelial shrinkage and pillar cells coarctation were comparatively associated to higher exposure dose. LDA with only "epithelial shrinkage", "epithelial swelling" and "pillar cells coarctation" in the model classified correctly 87.5% of the cross-validated cases. A possible pathogenetic relationship between the discriminant elementary lesions and the toxic mode of action at the cellular level of both cadmium and terbuthylazine is also discussed.

Occurrence of immune cells in the intestinal wall of Squalius cephalus infected with Pomphorhynchus laevis.

A sub-population of 34 specimens of chub, Squalius cephalus, was sampled from the River Brenta (Northern Italy) and examined for ecto- and endo-parasites. Pomphorhynchus laevis (Acanthocephala) was the only enteric helminth encountered. Immunofluorescence and ultrastructural studies were conducted on the intestines of chub. Near the site of parasite's attachment, mucous cells, mast cells (MCs), neutrophils and rodlet cells (RCs) were found to co-occur within the intestinal epithelium. The numbers of mucous cells, MCs and neutrophils were significantly higher in infected fish (Mann-Whitney U test, p < 0.05). Dual immunofluorescence staining with the lectin Dolichos Biflorus Agglutinin (DBA) and the macrophage-specific MAC387 monoclonal antibody, with parallel transmission electron microscopy, revealed that epithelial MCs often made intimate contact with the mucous cells. Degranulation of a large number of MCs around the site of the acanthocephalan's attachment and in proximity to mucous cells was also documented. MCs and neutrophils were abundant in the submucosa. Immune cells of the intestinal epithelium have been described at the ultrastructural level and their possible functions and interactions are discussed.