Phagocytosis by the endocardial lining cells of the atrium of plaice (Pleuronectes platessa)

Scavenger endothelial cells of fish, a review

The definition of scavenger endothelial cells (SEC) is exclusively based on functional and structural characteristics. The following characteristics are common hallmarks for the vertebrate SEC: (a) All vertebrates examined are furnished with a population of special SEC that plays a role in the catabolism of physiologic and non-physiologic soluble waste macromolecules. (b) From the ligands that are endocytosed, SEC in all seven vertebrate classes appear to express the collagen α-chain receptor and the scavenger receptors. In addition, the hyaluronan and the mannose receptors are present on SEC of mammalia (several species) and osteichthyes (e.g., salmon and cod). It is likely that all four receptor types are present in all vertebrate classes. (c) Like liver endothelial cells (LEC) in mammals, SEC in all vertebrate classes are geared to endocytosis of soluble macromolecules, but phagocytic uptake of particles is taken care of mainly by macrophages. (d) The most primitive vertebrates (hagfish, lamprey and ray) carry their SEC in gill vessels, whereas phylogenetically younger fishes (salmon, carp, cod and plaice) carry their SEC in either kidney or heart and in all terrestrial vertebrates-SEC are found exclusively in the liver. (e) SEC of all vertebrates are localized in blood sinusoids or trabeculae that carry large amounts of slowly flowing and O₂ poor blood. (f) SEC differs functionally and structurally from what is normally associated with "conventional vascular endothelium."

Interaction of Francisella noatunensis subsp. orientalis with Oreochromis mossambicus bulbus arteriosus cell line

Francisella noatunensis subsp. orientalis (Fno) (syn. F. asiatica) is an emergent warmwater fish pathogen and the causative agent of piscine francisellosis. Although Fno causes septicemia and can live extracellularly in infected tilapia (Oreochromis spp.), the early interaction of Fno with vasculature endothelium is unknown. In the present study, we examined the interaction of wild-type Fno (WT) and two Fno knockout [intracellular growth loci C (ΔiglC) and pathogenicity determinant protein A (ΔpdpA)] strains with the endothelial O. mossambicus bulbus arteriosus cell line (TmB) at 25 °C and 30 °C. Similar amounts of WT, ΔiglC, and ΔpdpA attached and were detected intracellularly after 5 h of incubation at both temperatures; however temperature affected attachment and uptake. While significantly greater amounts of Fno (WT, ΔiglC, and ΔpdpA) were detected intracellularly when TmB cells were incubated at 30 °C, bacteria attached to TmBs at greater levels at 25 °C. Only WT Fno was able to replicate intracellularly at 25 °C, which resulted in Fno mediated cytotoxicity and apoptosis at 24 and 72 h post-infection. WT Fno incubated at 30 °C as well as ΔiglC, and ΔpdpA incubated at 25 °C and 30 °C were all defective for survival, replication, and the ability to cause cytotoxicity in TmB. Taken together, these results demonstrate that temperature plays a vital role for Fno intracellular survival, persistence and cytotoxicity.

On endocytosis of foreign ferritin and occurrence of phagolysosomes in fish heart endothelial cells

In the present study the ultrastructure and function of the endothelial cells enveloping the muscle trabeculae in heart in two teleosts, platyfish and firemouth cichlid, are described and discussed. These cells displayed a structure making them able to take up large amounts of foreign ferritin particles from the blood stream. The ferritin particles were assembled into huge phagolysosomes. Large amounts of Prussian blue were precipitated throughout these lysosomes when treated with acid ferrohexacyanide solution. The occurrence of Prussian blue precipitations in the control heart endothelial cells after Schmorl's solution, suggests that these cells normally contain undigestible material, a finding which strengthens the view that this tissue is involved in blood clearance in the present species. In conclusion, these heart endothelial cells seem able to perform a very efficient blood clearance of scavenger and foreign macromolecules and particles in the present species.

Fate of intraperitoneally injected fluorescent microspheres in developing Ictalurus punctatus

Fluorescent microspheres (FMS) were injected intraperitoneally into channel catfish fry at 2 days post hatch (dph), 1, 2, 3, 4 and 8 weeks post hatch (wph). The FMS were observed in the vasculature almost immediately after injection in all age groups except 2 dph. Fluorescent microspheres were observed within mononuclear phagocytes in the vasculature after 0.16 dph in all age groups. Fluorescent microspheres were first phagocytized in the coelomic cavity immediately after injection, while the majority of coelomic FMS were phagocytized between 0.16 and 1 dph for all ages. Enzyme cytochemical staining indicated that both polymorphonuclear (neutrophilic granulocytes) and mononuclear phagocytes had phagocytized FMS in the coelomic cavity and organs, with a predominance of FMS found in mononuclear phagocytic cells in all age groups across all sample periods. The predominant organs associated with the observed cellular responses were the posterior kidney, spleen, and anterior kidney. Splenic organization and melanomacrophage development and activity were more pronounced as the fish aged from 2 wph on. Particulate clearance rates were faster in the 2 dph and 1 wph fish than the older ages of fish. These results suggest that to facilitate particulate retention, channel catfish should be vaccinated at 4 wph or older.

Molecular studies on the seasonal occurrence and development of five myxozoans in farmed Salmo trutta L

Five myxozoan species, Tetracapsuloides bryosalmonae, Sphaerospora truttae, Chloromyxum schurovi, Chloromyxum truttae and a Myxobolus species were detected in farmed brown trout, Salmo trutta L. from Central Scotland. Using PCR and in situ hybridization, this study investigated the seasonal occurrence and tissue location of these species in young of the year brown trout. C. schurovi, C. truttae and Myxobolus sp. were first detected in brown trout in April, 2 months before T. bryosalmonae and S. truttae. T. bryosalmonae and S. truttae showed proliferation in the blood with intravascular stages of T. bryosalmonae accumulating in the heart. In contrast, only small amounts of PCR products of C. schurovi and C. truttae were obtained from the blood, suggesting that these species use the vascular system for transport but proliferate only in their target tissues from which large amounts of PCR product were obtained and where parasites were visible in histological sections. Large amounts of PCR product were obtained for T. bryosalmonae, S. truttae and both Chloromyxum species from the gills of brown trout, suggesting the gills as entry locus for these species. The neurotropic Myxobolus species formed plasmodia predominantly in the peripheral nerves, possibly indicating an entry route through the skin. Presporogonic stages of all other species had disappeared by September and mature spores were present from August onwards.

Reticulo-endothelial stroma of the head-kidney from the seawater teleost gilthead seabream (Sparus aurata L.): an ultrastructural and cytochemical study

BACKGROUND

Head-kidney, considered the major fish lympho-haemopoietic tissue, consists of cells of the different haemopoietic series supported by a network of stromal cells whose morphofunctional properties have not been established. We report the ultrastructure and cytochemical features of the reticulo-endothelial stroma of the head-kidney from the seawater teleost gilthead seabream (Sparus aurata L.).

METHODS

Samples of head-kidney were processed for electron microscopic study. Some of the samples were incubated for acid and alkaline phosphatase, peroxidase, glucose-6-phosphatase, or ATPase.

RESULTS

The reticulo-endothelial stroma of gilthead seabream head-kidney consists of sinusoidal cells (endothelial and adventitial cells) and reticular cells (macrophage-type reticulum and fibroblast-like reticular cells). Transcytosis vesicles and rounded medium electron-dense granules were observed in the cytoplasm of the endothelial cells. The adventitial cells partially covered the outside surface of the endothelial cells and were joined by desmosomes. The macrophage-type reticulum cells were characterized by their cytoplasmic processes and acid phosphatase positive lysosomes. The fibroblast-like reticular cells were joined by desmosomes and formed an extensive network between the haemopoietic parenchyma. They were peroxidase negative and acid and alkaline phosphatase, glucose-6-phosphatase, beta-glucuronidase, and ATPase positive.

CONCLUSIONS

The ultrastructural and cytochemical features of the reticulo-endothelial stroma of the gilthead seabream head-kidney are similar to those of mammalian bone marrow, suggesting phylogenetic analogies between both tissues.

Melano-macrophage centre-like structure in the heart of the medaka, Oryzias latipes

Endocardial lining cells in the heart of certain teleosts are phagocytic against foreign materials. In the medaka Oryzias latipes, in addition to the endocardial lining cells, cells in the subendocardial spaces are also phagocytic. Most subendocardial cells contain yellowish-brown pigments and are often aggregated to form nodules resembling splenic and kidney melano-macrophage centres. Subendocardial cells are positive to PAS and Schmorl's reaction. Macrophages containing large heterogeneous inclusions together with lymphocytes, were observed with the TEM. The definitive characteristics of reticular cells, including the cell sheaths, were not observed. Because of these two characteristics they were regarded as more primitive aggregates of macrophages than the ordinary melano-macrophage centres. The possible analogy between these structures and MMCs is discussed.

Resident sinusoidal macrophages in the liver of the brown bullhead (Ictalurus nebulosus): an ultrastructural, functional and cytochemical study

Ultrastructural, functional, and cytochemical characteristics of resident sinusoidal macrophages (RSM) in brown bullhead (Ictalurus nebulosus) liver were examined. Following perfusion fixation of the hepatic vascular bed, light micrographs revealed RSM that possessed multiple elongate cytoplasmic processes and frequently contained erythrocytes in various stages of degradation. Following brief perfusion fixation, light microscope examination of vibratome sections of bullhead liver reacted for peroxidase revealed intensely positive RSM. By transmission electron microscopy, peroxidase activity was localized to the nuclear envelope and cytoplasmic granules of RSM and in endothelial and perisinusoidal fat-storing cells. In cryostat sections of fresh-frozen liver, glucose-6-phosphate dehydrogenase (G-6-PDH) was uniformly distributed over hepatocytes, whereas intensely positive punctate staining for G-6-PDH was localized over RSM. To test for phagocytosis by RSM, latex beads (0.81 micron) were injected into a tributary of the hepatic portal vein 2 min prior to perfusion fixation. Latex beads appeared either singly or in dense aggregates within RSM. Ultrastructurally, RSM were characterized by an irregularly shaped, eccentrically located nucleus, electron-dense vacuoles, small patches of granular endoplasmic reticulum, a well-developed Golgi apparatus, elongated mitochondria, desmosomes or desmosome-like densities that served as a source of attachment to endothelial cells, and a centriole with radiating microtubules. Invaginations of the plasma membrane (vermiform processes) characteristic of mammalian Kupffer cells were not observed in bullhead RSM. The results indicated a resident cell population of sinusoidal macrophages in the bullhead liver with properties that partially resembled mammalian Kupffer cells. These results are important for the identification of the normal resident cells in the bullhead liver.

Endocytosis of horse-spleen ferritin by bony fish endocardium

The endocytic uptake of horse-spleen ferritin by the endocardial cells in 2 bony-fish species, Xiphophorus helleri and Pollachius virens, is described. In specimens of X. helleri injected intraperitoneally by a ferritin solution 1/10 h before the sacrifice, the endocardial bristle-coated vesicles, cytoplasmic tubules, and endosomes (smooth vesicles of variable size) contain a number of ferritin particles. These particles are taken up by the bristle-coated vesicles, transferred through the cytoplasmic tubules, and emptied into the endosomes. The latter get more tightly packed by ferritin and increase in size with the time elapsed between the injection and sacrifice. After 9 h, most ferritin-packed endosomes (4 to 6 micron) contain fragments of those inclusion bodies (0.5 to 1.5 micron) which normally occur in the teleostean endocardium, and are therefore regarded as lysosomes. The ferritin-rich lysosomes increase greatly in size with time and display a width of 6 to 12 micron after 28 h. The number of cytoplasmic tubules declines rapidly with time, whereas there is a constant production of new endosomes, which probably are derived from the former. The ferritin particles are not accumulated in the endothelium of the bulbus arteriosus, whereas the hepatic endothelial cells take up some small amounts of ferritin. A similar uptake of ferritin as described above was also observed in the heart of P. virens when perfused by a ferritin solution for 3 h. The present results are discussed and compared with those previously reported for the uptake of ferritin in various tissues in fishes and mammals.(ABSTRACT TRUNCATED AT 250 WORDS)

Opsonic effect of rainbow trout (Salmo gairdneri) antibody on phagocytosis of Yersinia ruckeri by trout leukocytes

Partly purified peripheral blood leukocytes from normal rainbow trout (Salmo gairdneri) were used to study the influence of specific antibody on phagocytic uptake and intracellular killing of Yersinia ruckeri, a bacterial pathogen of trout. Specific antibody exerted a significant opsonic effect on the rate of phagocytic ingestion of the bacteria but did not affect the rate of intracellular killing. The results are discussed with reference to the current understanding of fish antibody function and phagocytosis by fish leukocytes.

The quantitative clearance of bacteria from the bloodstream of rainbow trout (Salmo gairdneri)

The blood clearance of 51Cr-labelled heat-killed Salmonella pullorum was biphasic and exponential for each phase. This pattern was the same for all three concentrations of bacteria used. The initial more rapid phase lasted for approximately 15 minutes when roughly 90% of the bacteria had been cleared. The second slower phase started 25 to 30 minutes post-inoculation and lasted for approximately 25 to 30 minutes. The tissue distribution of bacteria showed that in both absolute and relative terms, the kidney was the most important organ, accounting for more than 70% uptake of the bacteria. These kinetics demonstrate that rainbow trout at 8 degrees C are able to clear their bloodstream of Salmonella very efficiently, in a fashion very similar to mammals. It is not know, however, which of the various possible clearance mechanisms dominates each phase.