Figure 4: Virus titre detected in the supernatants of influenza virus-infected differentiated macrophages at an MOI of 2. Differentiated primary human macrophages were infected with influenza A/California/04/2009 virus (H1N1), A/Quail/Hong Kong/G1/97 (H9N2) or A/ Hong Kong/483/97 (H5N1) at MOI of 2. At 3, 6, and 24h post-infection, virus-infected culture supernatants were collected. Serial dilutions (from 0.5 log to 7 log) of supernatants were prepared before the addition of the culture supernatant onto a sub-confluent 96-well tissue culture plate of MDCK cells in quadruplicate. The plates were observed for a Cytopathic Effect (CPE) daily. The endpoint of viral dilution leading to CPE in 50% of inoculated wells was estimated by using the Karber method. The chart showed the median and the standard error of the virus titre pooled from three independent experiments.