In addition, the mRNA expression levels of proinflammatory cytokines downstream of the RIG-I/MDA5 pathway, including IL-6, IL-8 and TNF-α, were also significantly upregulated in the infection group than that in the control group at 12 hpi, 24 hpi and 48 hpi, respectively (Figure 3A). Here, CXCL8 is linked to infection.