Virus strains and HA vaccine
The type A influenza viruses used in this study were the mouse-adapted
A/Puerto Rico/8/1934 (H1N1) [PR8] viral strains obtained from ATCC.
Type A influenza viruses were propagated in MDCK cells in serum-free
media in the presence of TPCK-trypsin and the median tissue culture
infective dose (TCID50) and median lethal dose
(LD50) of the viruses were calculated. The HA vaccines
(viral vaccines) were prepared from influenza viruses, including
A/Puerto Rico/8/1934 (A/PR8:H1N1) strains, according to the method of
Jian et al . Briefly, we performed a plaque assay with MDCK and a
hemagglutination assay with serum to calculate the titer of virus stock.
The titer of virus stock showed that 1 hemagglutination unit (HAU) was
equal to 103 PFU. The PR8 virus stock were exposed to
ultraviolet light (UV) for 45
minutes.(Jian, Chang, Lin, Yang, &
Chuang, 2013) The loss of infectivity of the UVâinactivated PR8 virus
was confirmed by the plaque assay.