FIG 4.

Replication of A(H9N2) viruses in Calu-3 cells. Human bronchial epithelial (Calu-3) cells were grown on transwell inserts and infected apically in triplicate at an MOI of 0.01 with the indicated A(H9N2), A(H7N9) (Shanghai/1), 2009 pandemic A(H1N1) (Cal/7), or seasonal A(H3N2) (Switz/13) viruses. (A and B) Cells were incubated at 37°C (A) or 33°C (B). Culture supernatants were sampled at the indicated times p.i. and titrated in MDCK cells by standard plaque assay. (C) Comparison of infectious titers collected at 24 h p.i. from 37°C (black bars) and 33°C (gray bars) cultures is shown. The limit of virus detection was 10 PFU/ml.