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The present study determines the cytokine gene expression in chickens following RSV-A infection, using RT-qPCR. In susceptible chickens tumors progressed to  fulminating metastatic tumors while it regressed in  regressors  chickens and some resistant non-responder chickens did not respond to RSV-A infection and thus did not develop tumors at all. The in vivo expression of pro-inflammatory cytokines, Th1 cytokines and Th2 cytokines was determined at the primary site of infection, as well as in different organs of progressor, regressor and non-responder chicks at different time intervals. Our results indicated a significant upregulation of the pro-inflammatory cytokines, IL-6 and IL-8, in all the organs of progressor chicks, while they were significantly lower in regressor and non-responder chicks. The expression of the Th1 cytokines IFN-γ and TNF-α was low in all of the organs of the progressor group, except that in  spleen. In contrast, regressor and non-responder groups showed high expression of IFN-γ and TNF-α. Further, there was an early upregulation of the expression of the Th2 cytokine, IL-10, TGF-β and GM-CSF, in all of the organs of progressors as compared to uninfected control.

The Czech scientist Jan Svoboda was a pioneer of Rous sarcoma virus (RSV). In the 1960s, before the discovery of reverse transcriptase, he demonstrated the long-term persistence of the viral genome in non-productive mammalian cells, and he supported the DNA provirus hypothesis of Howard Temin. He showed how the virus can be rescued in the infectious form and elucidated the replication-competent nature of the Prague strain of RSV later used for the identification of the src oncogene. His studies straddled molecular oncology and virology, and he remained an active contributor to the field until his death last year. Throughout the 50 years that I was privileged to know Svoboda as my mentor and friend, I admired his depth of scientific inquiry and his steadfast integrity in the face of political oppression.

In my article I tried to present the results of early experiments suggesting a significant role for cell association in Rous sarcoma virus transformation of non-permissive cells and revealing that infectious virus can be efficiently rescued from such cells by their fusion with permissive chicken fibroblasts.

Unlabelled: Transformation of rodent cells with avian Rous sarcoma virus (RSV) opened new ways to studying virus integration and expression in nonpermissive cells. We were interested in (i) the molecular changes accompanying fusion of RSV-transformed mammalian cells with avian cells leading to virus rescue and (ii) enhancement of this process by retroviral gene products. The RSV-transformed hamster RSCh cell line was characterized as producing only a marginal amount of env mRNA, no envelope glycoprotein, and a small amount of unprocessed Gag protein. Egress of viral unspliced genomic RNA from the nucleus was hampered, and its stability decreased. Cell fusion of the chicken DF-1 cell line with RSCh cells led to production of env mRNA, envelope glycoprotein, and processed Gag and virus-like particle formation. Proteosynthesis inhibition in DF-1 cells suppressed steps leading to virus rescue. Furthermore, new aberrantly spliced env mRNA species were found in the RSCh cells. Finally, we demonstrated that virus rescue efficiency can be significantly increased by complementation with the env gene and the highly expressed gag gene and can be increased the most by a helper virus infection. In summary, Env and Gag synthesis is increased after RSV-transformed hamster cell fusion with chicken fibroblasts, and both proteins provided in trans enhance RSV rescue. We conclude that the chicken fibroblast yields some factor(s) needed for RSV replication, particularly Env and Gag synthesis, in nonpermissive rodent cells., Importance: One of the important issues in retrovirus heterotransmission is related to cellular factors that prevent virus replication. Rous sarcoma virus (RSV), a member of the avian sarcoma and leukosis family of retroviruses, is able to infect and transform mammalian cells; however, such transformed cells do not produce infectious virus particles. Using the well-defined model of RSV-transformed rodent cells, we established that the lack of virus replication is due to the absence of chicken factor(s), which can be supplemented by cell fusion. Cell fusion with permissive chicken cells led to an increase in RNA splicing and nuclear export of specific viral mRNAs, as well as synthesis of respective viral proteins and production of virus-like particles. RSV rescue by cell fusion can be potentiated by in trans expression of viral genes in chicken cells. We conclude that rodent cells lack some chicken factor(s) required for proper viral RNA processing and viral protein synthesis.

This study investigated the anti-neoplastic potential of avian reovirus σC (sigma C) protein on Rous sarcoma virus-induced fibrosarcoma in chicken. The recombinant vector expressing σC protein was injected intra-tumorally into specific pathogen free chicken with fibro-sarcoma at the dose 100µg per bird, while control birds were mock-treated with 100µg of empty vector per bird. Recombinant σC protein induced apoptosis in tumors of treated birds resulting in progressive tumor regression, while similar changes were absent in tumors of mock-treated controls. The σC protein-induced apoptosis in tumors was quantified by flow cytometry and the mean level of apoptosis up to 66% was observed in treated tumors, whereas any significant level of apoptosis was absent in mock-treated controls.