PR8 induction of NMB and NMBR expression. 293T and A549 cells were infected with PR8 (MOI = 1) and harvested at 0, 6, and 12 hpi, and lung tissues were harvested at 3 dpi, to measure the expression of NMB and NMBR by RT-PCR and qRT-PCR. A–C Expression of NMB and NMBR in 293T cells. D–F Expression of NMB and NMBR in A549 cells. G–I NMB and NMBR expression in mouse lungs. GAPDH, glyceraldehyde-3-phosphate dehydrogenase; NP, virus nucleoprotein; β-actin or GAPDH were used as reference housekeeping genes for internal standardization. *P < 0.05, **P < 0.01.