DEVELOPMENT OF A CONTINUOUS CELL LINE, PBLE, FROM AN AMERICAN EEL PERIPHERAL BLOOD LEUKOCYTE PREPARATION

Distinguishing between ante factum and post factum properties of animal cell lines and demonstrating their use in grouping ray-finned fish cell lines into invitromes

In this review, animal cell lines are considered to have two classes of attributes: "before-the-fact" (ante factum) and "after-the-fact" (post factum) properties. Fish cell lines from Actinopterygii (ray-finned fishes) are used to illustrate this distinction and to demonstrate how these properties can be used in various ways to categorize cell lines into groups or invitromes. Before-the-fact properties are set at initiation and are properties of the sample and species from which the cell line arose and of the scientist(s) who developed the cell line. On the basis of the Actinopterygii sample, invitromes exist for embryos, larvae, juveniles, adults, and spawning fish, and for most solid organs but rarely for biological fluids. For species, invitromes exist for only a small fraction of the Actinopterygii total. As to their development, scientists from around the world have contributed to invitromes. By contrast, after-the-fact properties are limitless and become apparent during development, characterization, use, and storage of the cell line. For ray-finned invitromes, cell lines appear to acquire immortality during development, are characterized poorly for differentiation potential, have numerous uses, and are stored formally only sporadically. As an example of applying these principles to a specific organ, the skeletal muscle invitrome is used. For ante factum properties, the cell lines are mainly from trunk muscle of economically important fish from 11 orders, 15 families, 19 genera, and 21 species of ray-finned fishes. For post factum properties, fibroblast-like and myogenic cell lines have been described but epithelial-like FHM is most widely used and curated. Considering cell lines by their before- and after-the-fact properties should facilitate integration of new cell lines into the literature and help incorporate the discipline of cell biology into other research areas, particularly the natural history of fishes.

Assessing Fish Immunotoxicity by Means of In Vitro Assays: Are We There Yet?

There is growing awareness that a range of environmental chemicals target the immune system of fish and may compromise the resistance towards infectious pathogens. Existing concepts to assess chemical hazards to fish, however, do not consider immunotoxicity. Over recent years, the application of in vitro assays for ecotoxicological hazard assessment has gained momentum, what leads to the question whether in vitro assays using piscine immune cells might be suitable to evaluate immunotoxic potentials of environmental chemicals to fish. In vitro systems using primary immune cells or immune cells lines have been established from a wide array of fish species and basically from all immune tissues, and in principal these assays should be able to detect chemical impacts on diverse immune functions. In fact, in vitro assays were found to be a valuable tool in investigating the mechanisms and modes of action through which environmental agents interfere with immune cell functions. However, at the current state of knowledge the usefulness of these assays for immunotoxicity screening in the context of chemical hazard assessment appears questionable. This is mainly due to a lack of assay standardization, and an insufficient knowledge of assay performance with respect to false positive or false negative signals for the different toxicant groups and different immune functions. Also the predictivity of the in vitro immunotoxicity assays for the in vivo immunotoxic response of fishes is uncertain. In conclusion, the currently available database is too limited to support the routine application of piscine in vitro assays as screening tool for assessing immunotoxic potentials of environmental chemicals to fish.

Development and characterization of a continuous cell line (EL) from the liver of European eel Anguilla anguilla

In the present study, a new hepatic tissue‐origin cell line from European eel Anguilla anguilla has been developed and characterized. This cell line designated EL has been maintained in Leibovitz L‐15 supplemented with 10% fetal bovine serum over 72 months, and subcultured more than 90 times. The EL cell line consisted predominantly of fibroblast‐like cells, which could survive over 100 days in vitro, and could grow at 15–32°C. The optimum temperature for growth was 27°C. The chromosome analysis revealed a modal diploid karyotype of 2n = 38. The origin of this cell line was confirmed by the 18S recombinant (r)RNA sequencing. The susceptibility test indicated significant cytopathic effects in the EL cells with regard to the Rana grylio virus and the Herpesvirus anguillae. The viral replication was confirmed by transmission electron microscopy and polymerase chain reaction analysis. Following poly (I:C) exposure, the expression levels of the immune‐related molecules interferon regulatory factor‐7 (irf7) and transforming growth factor‐β (TGF‐β) were downregulated in EL cells, whereas the expression levels of the rf3 and the cytochrome P450 (CYP450) were upregulated. All four genes were significantly upregulated following inflammation by lipopolysaccharide (LPS). These data suggested the application of EL cell line for viral identification, as well as for immunodiagnosis and pharmacological targeting.

Development and characterization of a new cell line derived from European eel Anguilla anguilla kidney

A new cell line derived from the kidney of European eel, Anguilla anguilla, has been established and characterized. This cell line, designated as EK (eel kidney), has been maintained in Leibovitz's L-15 supplemented with 10% fetal bovine serum for over 24 months, and subcultured more than 60 times. This cell line consists predominantly of fibroblast-like cells, and can grow at 15–37°C under an optimum temperature of 26°C. The origin of this cell line was confirmed by polymerase chain reaction (PCR) amplification and 18s recombinant (r)RNA sequencing. The chromosome analysis of EK cells at passage 58 revealed an ananeuploid karyotype. The EK cells were successfully transfected with the Pegfp-N1 plasmid, suggesting its potential in genetic studies. The susceptibility test showed a significant cytopathic effect (CPE) in EK cells for Rana grylio virus, and the viral replication was evidenced with quantitative real-time PCR (qRT-PCR) assay. After poly (I:C) stimulation, the expression of the immune-related molecules including interferon regulatory factor-3 (irf3), interferon regulatory factor-7 (irf7) and cytochrome P450 (CYP450) were significantly upregulated in EK cells, while the expression of transforming growth factor (TGF-β) was downregulated. These results suggested the potential of EK cell line as a model in gene engineering, virus identification and environmental toxicology.

Summary: The first visceral cell line of an endangered species, Anguilla anguilla has been established; this aneuploid cell line is fibroblast-like, and suitable for gene expression and virus isolation.

Responses of an American eel brain endothelial-like cell line to selenium deprivation and to selenite, selenate, and selenomethionine additions in different exposure media

The effect of selenium deprivation and addition on the American eel brain endothelial cell line (eelB) was studied in three exposure media: complete growth medium (L15/FBS), serum-free medium (L15), and minimal medium (L15/ex). L15/ex contains only galactose and pyruvate and allowed the deprivation of selenium on cells to be studied. In L15/ex, without any obvious source of selenium, eelB cells survived for at least 7 d, formed capillary-like structures (CLS) on Matrigel, and migrated to heal wounds. Three selenium compounds were added to cultures: selenite, selenate, and selenomethionine (SeMet). Adding selenite or selenate to eelB cell cultures for 24 h caused dose-dependent declines in cell viability, regardless of the exposure media. Although varying with exposure media and viability end point, selenite was approximately 70-fold more cytotoxic than selenate. By contrast, 24 h exposures to either DL- or L-SeMet in the three media caused little or no cytotoxicity. However for 7 d exposures in L15/ex, DL- and L-SeMet were very cytotoxic, even at the lowest tested concentration of 31 μM. By contrast in L15 and L15/FBS, cytotoxicity was only observed with 500 and 1000 μM L-SeMet. In L15/FBS, eelB continued to migrate and form CLS in the presence of SeMet but at 500 μM, cell migration appeared stimulated. As judged from a colony-forming assay over 14 d in L15/FBS, 500 and 1000 μM DL- and L-SeMet inhibited cell proliferation. Overall, the responses of eel cells to selenium depended on the selenium form, concentration, and exposure media, with responses to SeMet being most dependent on exposure media.

Establishment of a leukocyte cell line derived from peritoneal macrophages of fish, Labeo rohita (Hamilton, 1822)

A continuous leukocyte cell line with phagocytic activity was established from peritoneal macrophages of rohu, Labeo rohita (LRPM). LRPM was initiated from adherent mononuclear leukocytes isolated from peritoneal cavity of rohu, without use of any growth factors or feeder cells. These cells exhibited maximum growth at 30 °C in L-15 medium containing 20 % foetal bovine serum, and has been subcultured for more than 60 passages till date. The cells showed 85 % viability after 6 months of storage in liquid nitrogen. The species of origin of the LRPM was confirmed by the amplification and sequencing of 655 bp fragment of cytochrome oxidase subunit I of mitochondrial DNA. Functionally, LRPM showed phagocytic activity of yeast cells and fluorescent latex beads as evaluated by phase contrast and scanning electron microscopy, respectively. Immuno-modulators such as bacterial lipopolysaccharide and phorbol myristate acetate resulted in functional activation of LRPM; and enhanced their microbicidal activity through release of reactive oxygen species and nitric oxide. Culture supernatant from activated cells also revealed lysozyme activity. Cells of LRPM were positive for alpha-naphthyl acetate esterase enzyme indicating macrophage lineage. Our results indicate that this cell line can be a useful in vitro tool to study the role of macrophages in teleost immune system and to evaluate the effects of new aquaculture drugs. The LRPM cell line represents the first reported leukocyte cell line of peritoneal origin from any freshwater species of fish.

Development, characterization, conservation and storage of fish cell lines: a review

Cell lines provide an important biological tool for carrying out investigations into physiology, virology, toxicology, carcinogenesis and transgenics. Teleost fish cell lines have been developed from a broad range of tissues such as ovary, fin, swim bladder, heart, spleen, liver, eye muscle, vertebrae, brain, skin. One hundred and twenty-four new fish cell lines from different fish species ranging from grouper to eel have been reported since the last review by Fryer and Lannan (J Tissue Culture Methods 16: 87-94, 1994). Among the cell lines listed, more than 60% were established from species from Asia, which contributes more than 80% of total fish production. This includes 59 cell lines from 19 freshwater, 54 from 22 marine and 11 from 3 brackish water fishes. Presently, about 283 cell lines have been established from finfish around the world. In addition to the listing and a scientific update on new cell lines, the importance of authentication, applications, cross-contamination and implications of overpassaged cell lines has also been discussed in this comprehensive review. The authors feel that the review will serve an updated database for beginners and established researchers in the field of fish cell line research and development.

Development and characterization of a new epithelial cell line PSF from caudal fin of Green chromide, Etroplus suratensis (Bloch, 1790)

A new cell line [pearlspot fin (PSF)] has been developed from caudal fin of Etroplus suratensis, a brackish/freshwater fish cultivated in India. The cell line was maintained in Leibovitz's L-15 supplemented with 10% fetal bovine serum (FBS). The PSF cell line consisted predominantly of epithelial-like cells. The cells were able to grow at temperatures between 25 degrees C and 32 degrees C with optimum temperature of 28 degrees C. The growth rate of PSF cells increased as the FBS proportion increased from 2% to 20% at 28 degrees C with optimum growth at the concentration of 10% FBS. One marine fish virus (fish nodavirus) was tested on this cell line and found not susceptible. After confluency, the cells were subcultured with a split ratio of 1:2. The cells showed epithelial-like morphology and reached confluency on the third d after subculture. Polymerase chain reaction amplification of mitochondrial 16S rRNA and COI indicated identity of this cell line with those reported from this fish species, confirming that the cell line was of pearlspot origin. The cells were successfully cryopreserved and revived at the tenth, 25th, and 35th passages. The bacterial extracellular products from Vibrio cholerae MTCC 3904 were found to be toxic to PSF. Karyotyping analysis indicated that the modal chromosome number was 48.

Cytopathic effects of chum salmon reovirus to salmonid epithelial, fibroblast and macrophage cell lines

The cytopathic effect (CPE) of chum salmon reovirus (CSV), an aquareovirus, was studied in three salmonid cell lines: epithelial-like CHSE-214 from Chinook salmon embryo, fibroblast-like RTG-2, and monocyte/macrophage-like RTS11, both from rainbow trout. CHSE-214 and RTG-2 supported syncytia formation with more dramatic syncytia being observed in CHSE-214 cultures, while CSV induced homotypic aggregation (HA) in RTS11. Syncytia and HA formation were blocked by cycloheximide and ribavirin but not actinomycin D, suggesting that expression of CSV genes were required for both phenomena. Cultures with syncytia underwent a decline in cell viability, which appeared to be via apoptosis, as determined by intranucleosomal fragmentation and caspase dependence assays using the pan-caspase inhibitor, zVAD-fmk. In the presence of zVAD-fmk, CHSE-214 cultures continued to form syncytia and show diminished energy metabolism, but DNA fragmentation, the loss of membrane integrity, and the release of infectious CSV were considerably blocked. These results suggest that the formation of syncytia triggers apoptosis and a leaky plasma membrane, which enhances viral release. By contrast, RTS11 cultures undergoing HA showed no loss of cell viability. The significance of HA is unclear, but the response suggests that macrophage behaviour in rainbow trout potentially could be modulated by CSV.