Evidence for interferon production and its correlation with YF 17DD vaccine virus yields in primary chick embryo cells

Early experiments have resulted in the establishment of an efficient methodology for the production of a yellow fever vaccine in chicken embryo fibroblasts (CEF) using the 17DD virus strain [Freire, M.S., Mann, G.F., Marchevsky, R.S., Yamamura, A.M., Almeida, L.F., Jabor, A.V., Malachias, J.M., Coutinho, E.S., Galler, R., 2005. Production of yellow fever 17DD vaccine virus in primary culture of chicken embryo fibroblasts: yields, thermo and genetic stability, attenuation and immunogenicity. Vaccine 23, 2501–2512]. To investigate the role of the interferon system in vaccine virus yields, CEF cultures seeded at high and low cell densities and infected with the yellow fever 17DD virus were used. The supernatants of these cultures were tested for the presence of interferon by an assay based on the reduction of cytopathic effect of a challenge virus (Sindbis), for the enzymatic activity of the interferon-induced 2′,5′-oligoadenylate synthetase and for the expression of 2′,5′-oligoadenylate synthetase mRNA. The presence of interferon and its influence in the replication of yellow fever 17DD virus in CEF cultures was clearly demonstrated.