Survival of metazoan parasites in fish: Putting into context the protective immune responses of teleost fish

Defence mechanisms of fish can be divided into specific and non-specific that act in concert and are often interdependent. Most fish in both wild and cultured populations are vulnerable to metazoan parasites. Endoparasitic helminths include several species of digeneans, cestodes, nematodes, and acanthocephalans. Although they may occur in large numbers, helminth infections rarely result in fish mortality. Conversely, some ectoparasites cause mass mortality in farmed fish. Given the importance of fish innate immunity, this review addresses non-specific defence mechanisms of fish against metazoan parasites, with emphasis on granulocyte responses involving mast cells, neutrophils, macrophages, rodlet cells, and mucous cells. Metazoan parasites are important disease agents that affect wild and farmed fish and can induce high economic loss and, as pathogen organisms, deserve considerable attention. The paper will provide our light and transmission electron microscopy data on metazoan parasites-fish innate immune and neuroendocrine systems. Insights about the structure and functions of the cell types listed above and a brief account of the effects and harms of each metazoan taxon to specific fish apparati/organs will be presented

Ultrastructural assessment of granulomas in the liver of perch (Perca fluviatilis) Infected by tapeworm

Granulomas caused by migration of larvae of a helminth parasite, Triaenophorus nodulosus, within the liver of perch (Perca fluviatilis) from Rimov Dam Lake (Czech Republic) were assessed by transmission electron microscopy. Lesions were found in the liver of 29 out of 34 perch examined (85.2%) and there were between 1 and 15 T. nodulosus larvae identified per host. Pathological changes were more severe in livers containing more granulomas. Within the granulomas, there were three concentric regions: an outer layer of fibrous connective tissue, a middle clear epithelioid layer and a central dark spindle cell layer. The outer layer contained mast cells, fibroblasts, thick collagen bundles and epithelioid cells. The granulomas contained few lymphocytes and macrophages. Hepatocytes adjacent to the granulomas showed pronounced degeneration (ranging from vacuolar degeneration to acute cellular swelling)

Involvment of mucous cells in the protective response of fish against enteric parasites

No abstract availabl

Crustacean-acanthocephalan interaction and host cell-mediated immunity: parasite encapsulation and melanization.

Host-parasite interactions of Pomphorhynchus laevis (Müller, 1776) in naturally infected amphipod, Echinogammarus stammeri (Karaman, 1931), from the River Brenta (northern Italy) are described. A fully developed acanthocephalan larva occupies a large portion of an amphipod’s haemocoelic space; thus, the parasite frequently induces displacement of host digestive tract and other internal organs. However, no apparent damage to the host’s internal structures was observed. Within the haemocoel of E. stammeri, each larva of P. laevis is surrounded with a membranous layer, formed by microvilli, which maintains intimate contact with the amphipod’s internal organs and haemocytes. Three types of circulatory haemocytes were identified based upon their distinct appearance: hyaline cell, semi-granular cell and granular cell. Echinogammarus stammeri haemocytes surrounded acanthocephalan larvae and in some instances a partially and/or totally melanized P. laevis larva was noticed. Interestingly, no melanized larvae were found in E. stammeri parasitized with other acanthocephalans namely Echinorhynchus truttae (Schrank, 1788), Polymorphus minutus (Goeze, 1782) and Acanthocephalus clavula (Dujardin, 1845)

Lectin histochemistry of intestinal mucous and mast cells in helminth-infected fish.

Lectins, proteins that bind the specific carbohydrate structures, are ubiquitous and are found in animals, plants and microorganisms. Eight biotinylated lectins linking carbohydrates were used on the deparaffinised, hydrated uninfected and helminth-infected intestinal sections of chub Squalius cephalus and brown trout, Salmo trutta. The reaction of each lectin was determined through the use of avidin DH-biotinylated horseradish peroxidase and the DAB chromogen. A diverse array of lectin/carbohydrate responses were seen across the two fish species. DBA, PNA, UEA I and WGA were seen on trout mucous cells, while only DBA and PNA were seen on the mucous cells in chub. Parasite presence was seen to induce changes in the mucus carbohydrate composition of the fish's intestine.Numerous mucous cells reactive to DBA-PNA and UEA I subsequently appeared in parasitised chub and trout. The responsiveness of the mucous cells, however, is not dependent on the type of parasite infecting the host, as similar lectin patterns were seen in trout intestines infected with acanthocephalans and cestodes. Lectin histochemistry also highlights the responsiveness of mast cells (MCs), a type of granulocyte which are present in most tissues and are strategically positioned near blood vessels, in the connective tissue of chub (PNA-SNA) and trout (SNA). This comparative study between cestodes and acanthocephalans and their effects on the distribution of various lectins in the intestines of two fish represents a first record

Ultrastructure of male Centrorhynchus globocaudatus (Acanthocephala) cement apparatus and function of cement gland secretion

Cement glands are one of the most conspicuous and distinctive elements of taxonomic interest in male Acanthocephala. Cement glands vary in shape, number and arrangement in different classes of the taxon. The glands and their products have a fundamental role in the reproductive process. Light and electron microscopy were used to investigate the ultrastructure of the cement apparatus, which includes both cement glands and the cement reservoir, in mature males of Centrorhynchus globocaudatus (Zeder, 1800). Centrorhynchus globocaudatus is an enteric parasite of birds of prey, including Falco tinnunculus (Linnaeus, 1758) and Buteo buteo (Linnaeus, 1758) from the province of Ferrara (northern Italy). The four elongated cement glands of C. globocaudatus are situated posterior to the testes. Sections through the cement glands show each gland is surrounded by a fibrous envelope with an approximate thickness of 0.6 μm. Beneath this envelope is an outer cytoplasmic layer thickness ranging from 22 to 26 μm, which contains a number of nuclei with diameters variable from 20 to 22 μm. The cytoplasmic layer is filled with prominent free ribosomes and many mitochondria with lamellar cristae. Secretory granules, measuring from 1 to 1.3 μm in diameter, are formed within the cytoplasmic layer. The cytoplasmic layer surrounds the luminal area for storage of the cement material in each gland. Cement gland ducts arise from the gland and extend towards a common cement reservoir in close contact with the seminal vesicle and Saefftigen's pouch. Microtubules, large secretory granules and rest of undefined organelles were also observed within the cement reservoir

Fish cells involved in mucosal immunity against enteric helminths.

In recent decades, the mucosal immunology of higher vertebrates has been an intensively explored area of research and yet little is known regarding this in fish. The intestinal mucosa is continuously exposed to a broad spectrum of antigens derived from ingested food, water, commensal flora and pathogens. Recent comparative histological and ultrastructural studies on the uninfected intestines of chub Squalius cephalus, European eels Anguilla anguilla, and catfish Silurus glanis and in conspecifics naturally infected with acanthocephalans and platyhelminths, however, have begun to explore this. Endoparasitic helminths frequently cause intestinal inflammation inducing the recruitment of various immune cells to the site of infection. In each of the fish-helminth systems that were studied, a massive hyperplastic granulocyte response involving mast cells (MCs) and neutrophils in the epithelia, lamina propria and submucosa was seen in close proximity to the point of parasite attachment. An increase in the number of rodlet cells (RCs) in the intestinal epithelium of parasite-infected specimens was also seen. Hyperplasia and hypertrophy of mucous cells in infected intestines was evident. In transmission electron microscopy sections of all three infected fish hosts, MCs and mucous cells were frequently seen in contact with one another with evident degranulation of those MCs in close proximity to mucous cells. In fish the mechanism by which mucosal MCs might induce the secretion of excess mucus is unknown and is the main focus of this study. The role of MCs, neutrophils, RCs and mucous cells in the mucosal immune system of fish will be discussed

Rodlet cells, fish immune cells and a sentinel of parasitic harm in teleost organs

Rodlet cells (RCs) are the enigmatic and distinctive pear-shaped cells had found in many tissues of marine and freshwater teleosts. They have a distinctive fibrous capsule or the cell cortex that envelopes conspicuous inclusions called rodlets, basally situated nucleus, and poorly developed mitochondria. The contraction of the cell cortex results in the expulsion of the cell contents through an apical opening. One hundred and thirty years since rodlet cells were first reported, many questions remain about their origin and a function. This review will present new evidence regarding the relationship between RCs and metazoan parasites, and a protozoan infecting organs of different fish species, and update the state of knowledge about the origin, structure and the function of these intriguing fish cells