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Vaccinia virus (VACV) is an enveloped DNA virus from the Orthopoxvirus family, various strains of which were used in the successful eradication campaign against smallpox. Both original and newer VACV-based replicating vaccines reveal a risk of serious complications in atopic individuals. VACV encodes various factors interfering with host immune responses at multiple levels. In atopic skin, the production of type I interferon is compromised, while VACV specifically inhibits the phosphorylation of the Interferon Regulatory Factor 3 (IRF-3) and expression of interferons. To overcome this block, we generated a recombinant VACV-expressing murine IRF-3 (WR-IRF3) and characterized its effects on virus growth, cytokine expression and apoptosis in tissue cultures and in spontaneously atopic Nc/Nga and control Balb/c mice. Further, we explored the induction of protective immune responses against a lethal dose of wild-type WR, the surrogate of smallpox. We demonstrate that the overexpression of IRF-3 by WR-IRF3 increases the expression of type I interferon, modulates the expression of several cytokines and induces superior protective immune responses against a lethal poxvirus challenge in both Nc/Nga and Balb/c mice. Additionally, the results may be informative for design of other virus-based vaccines or for therapy of different viral infections.

In most cells, vaccinia virus (VACV) infection is considered to cause a lytic cell death, an equivalent of necrosis. However, upon infection of the epithelial cell lines HeLa G and BSC-40 with VACV strain Western Reserve (WR), we have previously observed an increased activation of and activity attributable to caspases, a typical sign of apoptosis. In this paper, we have further analyzed the type of cell death in VACV-infected cells HeLa G and BSC-40. In a cell-based flow cytometric assay, we showed a specific activation of caspase-2 and 4 in HeLa G and BSC-40 cells infected with VACV, strain WR, while we did not find any effects of inhibitors of calpain and cathepsin D and E. The actual activity of the two caspases, but also of caspase-3, was then confirmed in lysates of infected HeLa G, but not in BSC-40 cells. Accordingly, poly(ADP)-ribose polymerase (PARP) cleavage was found increased only in infected HeLa G cells. Consequently, we have determined morphological features of apoptosis and/or activity of the executioner caspase-3 in infected HeLa G cells in situ, while only a background apoptosis was observed in infected BSC-40 cells. Finally, vaccination strains Dryvax and Praha were found to induce apoptosis in both HeLa G and BSC-40 cells, as characterized morphologically and by PARP cleavage. These findings may be important for understanding the differences in VACV-host interactions and post-vaccination complications in different individuals., (Copyright © 2011 Elsevier B.V. All rights reserved.)