Knockout of C5aR1 led to an apparent reduction in susceptibility to EV-A71 infection in mice, as illustrated by the alleviation of clinical symptoms (Fig. 4D through F and N) and an increase in survival rate (Fig. 4G), as well as significant reductions in viral load (Fig. 4H) and proinflammatory cytokine (CXCL1, IL-1β, and MCP-1) (Fig. 4I through M) levels in these mice upon viral infection. This evidence concerns the gene CCL2 and viral infectious disease.