While IRF3 and IRF7, two of the first key immune genes to be activated, were also members of class 3, these two genes were barely or negatively correlated with the PRRs (Figure 5C, upper triangle), and these PRRs were not clustered in class 4, the immune-related class (Figure 5C, upper triangle, Y-axis tags), implying that at the early infection stage, the PRRs in fish did not yet initiate the downstream immune response, but the organism had already begun to produce IFN to defend against the viruses. This evidence concerns the gene IRF3 and infection.