CCL2 and infection: Additionally, severe influenza virus infection was associated with hypercytokinemia, including increased cytokine (IFNβ, TNF, IL-10 and IL-12p70) and chemokine (MCP-1 (CCL2), KC (CXCL1), IP-10 (CXCL10) and RANTES (CCL5)) levels in the severe infection group at 7 dpi (Supplementary Fig. 5c).