Expression changes of the proinflammatory cytokine genes and chemokine genes: the recruitment of innate immune cells into the lungs combined with excessive proinflammatory cytokine and chemokine production are hallmarks of influenza virus infection. We did not find significant changes in proinflammatory cytokine gene expression at 24 h after inoculation with H9N2 virus and viral particles. Chemokines are involved in the recruitment of circulating leukocytes into the inflamed tissues.