Establishment of an immortal turkey turbinate cell line suitable for avian metapneumovirus propagation

Evaluation of DF-1 cell culture based vaccine development for infectious bursal disease virus in Ethiopia

Infectious Bursal Disease is a highly contagious, immunosuppressive viral disease of young chicks caused by the Infectious Bursal Disease Virus (IBDV). The study was carried out at the National Veterinary Institute (NVI) of Ethiopia to evaluate the competence of the DF-1 cell culture adapted vaccine strain of IBDV as a vaccine candidate. DF-1 cells at passage 27 confluent monolayer was infected with 1 ml of LC-75 vaccine strain virus by adsorption method and recorded as passage 1 (P1). This procedure has been repeated up to seven serial passages with the same methods of virus infection onto DF-1 cells. Minor CPEs were observed in the second passage, but vivid cytopathic effects (CPE) were observed starting from passage 3 (P3). The infectivity titer of DF-1 cell adapted virus was determined, and the results showed a linear increase in titer with each passage number. Transcriptase polymerase chain reaction (RT-PCR) targeting the VP2 gene revealed positive 400-base pair amplification. The vaccinated experimental chicks from passages 5 and 7 and the CFC based vaccine showed no clinical signs and/or death. Efficacy test revealed that DF-1 adapted vaccinal strain protected the chicks from the challenged virus strain at passage 5 and 7. The control group, on the other hand, had 100 % morbidity and 91 % mortality. As a result, the DF-1 cell could be used as a model to study IBDV kinetic growth, and the DF-1 cell adapted virus could be a candidate for IBD vaccine development. Thus, IBD vaccine production using DF-1 cells is recommended.

Establishment and evaluation of the goose embryo epithelial (GEE) cell line as a new model for propagation of avian viruses

In this study, we report the establishment and characterization of a new epithelial cell line, goose embryonated epithelial cell line (GEE), derived from embryonic goose tissue. The purified GEE cell line can efficiently grow over 65 passages in the M199 medium supplemented with 10% fetal bovine serum at 37°C. Immunofluorescence assay was used to identify purified GEE cells as epithelial cell line by detecting expression of the Keratin-18 and -19. Further characterizations demonstrated that the GEE cell line can be continuously subcultured with (i) a high capacity to replicate for over 65 passages, (ii) a spontaneous epithelial-like morphology, (iii) constant chromosomal features and (iv) without an evidence of converting to tumorigenic cells either in vitro or in vivo study. Moreover, the GEE cell line can be effectively transfected with plasmids expressing reporter genes of different avian viruses, such as VP3, VP1 and F of goose parvo virus (GPV), duck hepatitis virus (DHV), and Newcastle disease virus (NDV), respectively. Finally, the established GEE cell line was evaluated for avian viruses infection susceptibility. Our results showed that the tested GPV, DHAV and NDV were capable to replicate in the new cell line with titers a comparatively higher to the ones detected in the traditional culture system. Accordingly, our established GEE cell line is apparently a suitable in vitro model for transgenic, and infection manipulation studies.

Genome-wide differential gene expression in immortalized DF-1 chicken embryo fibroblast cell line

BACKGROUND

When compared to primary chicken embryo fibroblast (CEF) cells, the immortal DF-1 CEF line exhibits enhanced growth rates and susceptibility to oxidative stress. Although genes responsible for cell cycle regulation and antioxidant functions have been identified, the genome-wide transcription profile of immortal DF-1 CEF cells has not been previously reported. Global gene expression in primary CEF and DF-1 cells was performed using a 4X44K chicken oligo microarray.

RESULTS

A total of 3876 differentially expressed genes were identified with a 2 fold level cutoff that included 1706 up-regulated and 2170 down-regulated genes in DF-1 cells. Network and functional analyses using Ingenuity Pathways Analysis (IPA, Ingenuity® Systems, http://www.ingenuity.com) revealed that 902 of 3876 differentially expressed genes were classified into a number of functional groups including cellular growth and proliferation, cell cycle, cellular movement, cancer, genetic disorders, and cell death. Also, the top 5 gene networks with intermolecular connections were identified. Bioinformatic analyses suggested that DF-1 cells were characterized by enhanced molecular mechanisms for cell cycle progression and proliferation, suppressing cell death pathways, altered cellular morphogenesis, and accelerated capacity for molecule transport. Key molecules for these functions include E2F1, BRCA1, SRC, CASP3, and the peroxidases.

CONCLUSIONS

The global gene expression profiles provide insight into the cellular mechanisms that regulate the unique characteristics observed in immortal DF-1 CEF cells.

Passport, a native Tc1 transposon from flatfish, is functionally active in vertebrate cells

The Tc1/mariner family of DNA transposons is widespread across fungal, plant and animal kingdoms, and thought to contribute to the evolution of their host genomes. To date, an active Tc1 transposon has not been identified within the native genome of a vertebrate. We demonstrate that Passport, a native transposon isolated from a fish (Pleuronectes platessa), is active in a variety of vertebrate cells. In transposition assays, we found that the Passport transposon system improved stable cellular transgenesis by 40-fold, has an apparent preference for insertion into genes, and is subject to overproduction inhibition like other Tc1 elements. Passport represents the first vertebrate Tc1 element described as both natively intact and functionally active, and given its restricted phylogenetic distribution, may be contemporaneously active. The Passport transposon system thus complements the available genetic tools for the manipulation of vertebrate genomes, and may provide a unique system for studying the infiltration of vertebrate genomes by Tc1 elements.

A method for the rapid isolation of virus from cultured cells

A simple and efficient collection method using hypotonic burst to isolate virions from infected cultured cells is described. Distilled water treatment of avian metapneumovirus (AMPV)-infected cells with thorough mixing and repeated pipeting was considerably faster for virion collection in avian cells compared to the widely used freeze-thaw (F-T) method (30 min vs. 3-4 h). This method was also more effective for virion collection. The total number of virions recovered from AMPV-infected immortal turkey turbinate cells by the novel water lysis method was 3-fold higher than by the F-T method. This simple water lysis method can be applied to virion collection for other RNA viruses such as the paramyxoviruses that are used to infect cultured cells.

Species-specific deletion of the viral attachment glycoprotein of avian metapneumovirus

The avian metapneumovirus (AMPV) genome encodes the fusion (F), small hydrophobic (SH), and attachment glycoprotein (G) as envelope glycoproteins. The F and G proteins mainly function to allow viral entry into host cells during the early steps of the virus life cycle. The highly variable AMPV G protein is a major determinant for distinguishing virus subtypes. Sequence analysis was used to determine if any differences between avian or mammalian cell propagated subtype C AMPV could be detected for the 1.8kb G gene. As a result, the complete 1.8kb G gene was found to be present when AMPV was propagated in our immortal turkey turbinate (TT-1) cell line regardless of passage number. Surprisingly, AMPV propagated for 15 or more passages in mammalian Vero cells revealed an essentially deleted G gene in the viral genome, resulting in no G gene mRNA expression. Although the Vero cell propagated AMPV genome contained a small 122 nucleotide fragment of the G gene, no other mRNA variants were detected from either mammalian or avian propagated AMPV. The G gene truncation might be caused by cellular molecular mechanisms that are species-specific. The lack of viral gene deletions suggests that avian cell propagated AMPV will provide a better alternative host for live recombinant vaccine development based on a reverse genetics system.