Strain (accession, expression plasmid, protease for HA cleavage)
B/Hong Kong/8/1973 (K00425 phCMV1 HAT)
B/Victoria/2/1987 (FJ766840 phCMV1 HAT)
B/Yamagata/16/1988 (CY018765.1 phCMV1 HAT)
B/Florida/4/2006 (EU515992 phCMV1 HAT)
B/Bangladesh/3333/2007 (CY115255.1 pI.18 HAT)
B/Brisbane/60/2008 (KX058884.1 pI.18 HAT)
B/Brisbane/60/2008 (EPI753679 pEVAC HAT)
B/Phuket/3073/2013 (pEVAC HAT)
B/Colorado/06/2017 (pEVAC HAT)
B/Washington/2/2019 (EPI1368874 pEVAC HAT)
Schematic representation of the production of influenza B pseudotypes by plasmid transfection. (a) Using a 4 plasmid system, exogenous NA was added to the transfected cultures at least 8 h post-transfection. (b) Addition of protease, which is necessary for the production of influenza B pseudotypes is optimized to increase production titres by transfecting using a ‘checkerboard’ approach with different proteases (e.g., HAT, TMPRSS4, and TMPRSS2). Protease plasmid was added at a ratio of 1:1, 1:0.5, and 1:0.25 to HA plasmid DNA for rapid optimization in a 6 well plate format. All pseudotypes were harvested after 48 h in culture. ORCID: https://orcid.org/0000-0002-7978-3815