CCL4 and viral infectious disease: It is noteworthy that while the CCL3 and CCL4 levels were significantly increased in SARS-CoV-2 + IAV at 7 dpi (Fig. 4E and F, right), the CCL5 and CXCL9 were significantly higher in IAV + SARS-CoV-2 coinfection groups at 7 dpi than those of the SARS-CoV-2 + IAV group (Fig. 4G and H), suggesting potential differential immune responses by order of viral infections.