Among all recombinant viruses, we found that the PB2 mutant with K at 627 induced higher level of TNF-α, IP-10, MCP-1 and MIP-1α at both 3 and 6 days post-infection when compared to the wild type 627E virus and the other two PB2 mutants (Fig. 6). The gene discussed is CCL2; the disease is infection.