Yield Of Influenza Research Articles

Cold adaptation generates mutations associated with the growth of influenza B vaccine viruses

Seasonal inactivated influenza vaccines are usually trivalent or quadrivalent and are prepared from accredited seed viruses. Yields of influenza A seed viruses can be enhanced by gene reassortment with high-yielding donor strains, but similar approaches for influenza B seed viruses have been largely unsuccessful. For vaccine manufacture influenza B seed viruses are usually adapted for high-growth by serial passage. Influenza B antigen yields so obtained are often unpredictable and selection of influenza B seed viruses by this method can be a rate-limiting step in seasonal influenza vaccine manufacture. We recently have shown that selection of stable cold-adapted mutants from seasonal epidemic influenza B viruses is associated with improved growth. In this study, specific mutations were identified that were responsible for growth enhancement as a consequence of adaptation to growth at lower temperatures. Molecular analysis revealed that the following mutations in the HA, NP and NA genes are required for enhanced viral growth: G156/N160 in the HA, E253, G375 in the NP and T146 in the NA genes. These results demonstrate that the growth of seasonal influenza B viruses can be optimized or improved significantly by specific gene modifications.

Cold adaptation improves the growth of seasonal influenza B vaccine viruses

Gene reassortment has proved useful in improving yields of influenza A antigens of egg-based inactivated vaccines, but similar approaches have been difficult with influenza B antigens. Current regulations for influenza vaccine seed viruses limit the number of egg passages and as a result resultant yields from influenza B vaccine seed viruses are frequently inconsistent. Therefore, reliable approaches to enhance yields of influenza B vaccine seed viruses are required for efficient vaccine manufacture. In the present study three stable cold-adapted (ca) mutants, caF, caM and caB derived from seasonal epidemic strains, B/Florida/4/2006, B/Malaysia/2506/2004 and B/Brisbane/60/2008 were prepared, which produced high hemagglutinin antigen yields and also increased viral yields of reassortants possessing the desired 6:2 gene constellation. The results demonstrate that consistent improvements in yields of influenza B viruses can be obtained by cold adaptation following extended passage. Taken together, the three ca viruses were shown to have potential as donor viruses for the preparation of high-yielding influenza B vaccine viruses by reassortment.

Activity of selenazofurin against influenza A and B viruses in vitro.

Activity of the new antiviral compound selenazofurin was compared with the known active compounds ribavirin and amantadine against influenza A and B viruses. In experiments with Madin Darby canine kidney cells, selenazofurin inhibited the cytopathic effect and yield of influenza A/NWS/33 virus, with 50% effective dose ranges of 0.7 to 1.4 micrograms/ml (virus rating [VR], 1.3 to 1.4). The 50% effective dose range for ribavirin was 1.2 to 1.6 micrograms/ml (VR, 1.0 to 1.3), and for amantadine it was 9 micrograms/ml (VR, 0.9). Selenazofurin and ribavirin were similarly inhibitory to influenza B/Lee/40 virus, whereas amantadine was inactive. Selenazofurin appeared somewhat cytotoxic in these studies at concentrations as low as 1 micrograms/ml.

53] Virus yield-reduction assays for interferon with the influenza virus neuraminidase assay

Publisher Summary This chapter describes virus yield-reduction assays for interferon with the influenza virus neurarninidase assay. The measure of reduction in yield of influenza A virus neuraminidase in infected cell cultures is a sensitive and reproducible bioassay for various interferons. A recombinant virus X7(F 1 ) (HON2) 3 is the most interferon sensitive of 12 influenza viruses tested and also produced higher yields of neuraminidase in most cell cultures than the other influenza viruses. This recombinant virus produces neuraminidase even in some cells that fail to produce infectious virus, but the best yields of neuraminidase were in primary chicken embryo cell cultures, which do produce infectious virus. The production of X7(F 1 ) neuraminidase is measured by the thiobarbituric acid method with the glycoprotein fetuin as substrate or by a method with the synthetic substrate methoxyphenylneuraminic acid.

Inhibition of influenza C virus replication by actinomycin D, alpha-amanitin, and UV irradiation.

Actinomycin D and alpha-amanitin caused similar reductions in the yields of influenza A/WSN and influenza C/JBH/1/66 viruses in a chicken kidney cell culture system. Irradiation of host cells with UV light before virus infection also produced a similar reduction in yields of the two viruses. The results indicate a close similarity between the replication processes of influenza C and other orthomyxoviruses.

Blocking of the Virus-Enhancing Activity of 5-Methyl-2-d-ribobenzimidazole (MRB)

SummaryDibutyryl-cyclic AMP (db-cAMP, 1 mM) limits the yield of influenza B (Lee) virus in the chorioallantoic membrane from 13-day-old embryonated chicken eggs. In membranes treated with 5-methyl-2-D-ribobenzimidazole (MRB, 3.5 mM), db-cAMP partially or completely blocks enhancement of virus yield by MRB. Eagle's spinner medium does not by itself affect virus yield compared to the yield in a simpler control medium, but it reduces the enhancing effect of MRB by more than 75%.The author thanks Miss Huguette Viguet for excellent technical assistance.

The production and assay of Myxovirus influenza A/PR8 in suspension cultures of a continuous cell line of human origin (G2)

High yields of influenza A/PR8, comparable to those obtained in the 10-day chick embryo, were obtained using a low input multiplicity of infection in suspension cultures of a continuous line of mammalian cells (G2). By using the hemadsorption differential (HAD) count, a technique combining hemadsorption with viable cell counting, the progress of virus production can be assayed and correlated with the metabolic condition of the cells.