Inflammation is a hallmark feature of many influenza virus infections. To obtain insight into the inflammatory mechanisms involved in influenza H9N2 infection of human lung epithelial cells, A549 airway epithelial cells were infected with avian H9N2 virus and the expressions of pro-inflammatory cytokines (IL-1β, IL-6) and chemokine (IL-8) in these cells were examined by qPCR and ELISA. Moreover, the effect of silencing of p65 component of NF-κB in A549 cells infected with H9N2 virus on the expression and secretion of pro-inflammatory cytokines and chemokine and virus replication were evaluated by qPCR, ELISA, Immunocytochemistry and western blotting.
Avian H9N2 virus was able to cultivate in the human lung epithelial cell line (A549) and stimulate production of IL-1β, IL-6 and IL-8. Expressions of cytokine and chemokine genes were down-regulated to a significantly lower level (IL-1β after 24hours (P < 0.1) and 48hours(P < 0.01), IL-6 after 24 hours (p < 0.01) and IL-8 after 24 hours(p < 0.05)) in p65 knocked down A549 cells as compared with scramble shRNA cultured cells infected with H9N2 influenza virus. The amount of IL-6 and IL-1β proteins secreted into the culture medium was also decreased after silencing the p65 component of NF-κB in A549 cells infected with H9N2 influenza virus in different multiplicity of infections (MOI).
The results presented in this study provide the mechanism by which avian H9N2 virus induce inflammation in human lung epithelial cells. These findings will broaden our understanding of host innate immune mechanisms and the pathogenesis of H9N2 influenza viruses in human respiratory epithelium.