Inflammatory cells of teleostean fish: A review focusing on mast cells/eosinophilic granule cells and rodlet cells

Vertebrate organisms have evolved sophisticated immunological mechanisms for the recognition of self versus nonself. The immune system is functionally characterized by specificity, diversity, and memory but is based at the molecular level on highly diverse antigen receptors (T-cell receptor, TcR; immunoglobulin, Ig), which together with major histocompatibility complex (MHC) molecules allow the activation of the so-called immunocompetent cells (T- and B-lymphocytes) during the immune response. Development and functional activation of immune cells occur in specialized tissue microenvironments provided by the primary and/or secondary lymphoid organs. These lymphoid organs then, represent a higher-order morphological structure culminating from complex molecular, cellular and tissue interactions, and are an invariable feature of the vertebrate immune system.

Phylogeny of lower vertebrates and their immunological structures.

This chapter focuses on the cell and tissues of the immune system of fish. In teleosts, three types of granulocytes—heterophils, acidophils, and basophils—have been reported. There is enormous variation within the teleosts in both relative abundance and staining reaction of the granulocytes. In the carp, Cyprinus carpio, all three types of granulocytes are found in the blood. Among them, the heterophils and basophils are the least numerous and constitute 1% of the total eukocyte count. The acidophilic granulocytes are rather abundant and constitute 8% of the total leukocyte count. The acidophilic granules are peroxidase positive and contain round or irregular granules with heterogeneous contents. Migrating leukocytes in the basal mucosa and submucosa, as well as in the epithelium but not lymphoid aggregates, have been detected in the hagfish intestine. In the stingray, Dasyatis akajei , meningeal lymphohemopoietic masses appear predominantly in the telencephalon, diencephalon, and mesencephalon. Antigen-binding cells and antibody-producing cells have been found in the lymphohemopoietic tissue of the teleost kidney Recently, a higher number of Ig-positive cells have been found in the head kidney than in the spleen. They occur as scattered cells or forming small pyroninophilic cell clusters, especially after antigenic stimulation. It has been observed that that the cells of the pyroninophilic clusters corresponded to the plasma cell lineage with Ig-producing capacity and to the large lymphoid type plasma cells that gradually differentiate in these cell clusters.

1 - Cells and Tissues of the Immune System of Fish

In this review recent morphological and histochemical descriptions have been compiled of (mainly outer) features of all developmental stages of the Acanthocephala as well as what is known about the host's defence measures directed against these worms. From acanthors, for intance, it is documented how they escape melanization inside the haemocoel of a suitable intermediate host after they have been activated and released from their eggshell enclosure in the gut of the arthropod. Acanthors possess a complex set of eggshell-envelopes and interstices that fulfill different tasks. While the sequence of events inside the intermediate host's haemocoel is rather well known, what happens in paratenic hosts has been little studied. In final hosts the host-parasite interactions depend on the systematic affiliation of the parasite as well as the host and on the depth of penetration of each acanthocephalan species in the intestinal wall of the host. The mode of attachment also influences the microhabitat preference inside the gut. Mammals often reveal symptoms of high morbidity when infected with acanthocephalans, while fish seem to tolerate high intensities of worms deeply penetrating into their intestinal wall without showing pronounced symptoms of disease. The review also treats the subjects of host specificity, nutrient uptake and metabolism of the worms as well as their absorbance of metals and other elements. The high absorbance capacity for heavy metals suggests the usefulness of acanthocephalans as bioindicators.

Host-parasite interactions in Acanthocephala: a morphological approach.

During recent years considerable study has been made of the systemic immune system of fish, although less attention has been paid to local immunity at sites such as the gut, reproductive tract and skin. Recent work on the structure of gut-associated lymphoid tissue and other intestinal cell populations, the absorption of macromolecules from the intestinal lumen and the production of specific mucosal antibodies strongly suggests, however, that the gut of these lower vertebrates is immunocompetent. This review briefly deals with current concepts on the nature of gut-associated lymphoid tissues and other cell populations in the gut, intestinal and biliary immunoglobulin (Ig), antigen uptake and the significance of oral vaccination in the protection of commercially reared fish against infectious disease.

Gut immunology in fish: A review

The ultrastructure of the small intestinal granule cells (GC) of the rainbow trout (Salmo gairdneri) was studied in fry and fingerlings before the cells organized to form the stratum granulosum (SG) and in 12-month-old juveniles which possess a well-developed SG several cell diameters in thickness. The GC of juvenile trout exhibit a striking reduction in nucleolar numbers and in the quantity of rough endoplasmic reticulum relative to the GC of younger fish, but contain even greater numbers of large, electron-dense cytoplasmic granules. The final stages of cellular maturation therefore take place in the GC after their organization to form a layer, and the cells appear to lose their capacity to synthesize protein(s) for the cytoplasmic granules. Since the latter structures are, nevertheless, maintained in large numbers in mature GC, it is suggested that they function intact within the cell. No precursor to the granulated form of the GC was identified in the intestine, a result which suggests that the earlie...

Ultrastructure of the granule cells in the small intestine of the rainbow trout (Salmo gairdneri) before and after stratum granulosum formation

The ontogeny of the stratum granulosum within the small intestine of the rainbow trout (Salmo gairdneri) was related to the chronological age of the animal. The component granule cells were first seen many weeks after the development of the collagenous stratum compactum. It is therefore concluded that the granule cells do not perform a critical role in stratum compactum formation. In addition, it is proposed that the stratum granulosum develops because of resistance of the stratum compactum to cellular penetration.

The development of the stratum granulosum of the small intestine of the rainbow trout (Salmo gairdneri)

The histochemical nature of the protein within the large granules of the intestinal granule cells was examined in rainbow trout, Salmo gairdneri, from the time of earliest appearance of the cells in the lamina propria until a layer of granule cells was established in 12-month-old juveniles. At all times the granule cell granules contained large quantities of protein. This material appeared to be predominantly cationic in nature as judged from results obtained with alkaline fast green FCF together with deamination controls. In addition, there was no major acidic protein within the intestinal granule cell granules.

T. Bergeron

Papers

Ultrastructure of the granule cells in the small intestine of the rainbow trout (Salmo gairdneri) before and after stratum granulosum formation

The development of the stratum granulosum of the small intestine of the rainbow trout (Salmo gairdneri)

Protein histochemistry of the granule cells in the small intestine of the rainbow trout, Salmo gairdneri Richardson