The expression levels of RIG-I, MDA-5 and MAVS mRNA in PCV2-PIECs group were higher than those in the PIECs group at 12 and 24 h post-infection (hpi) (P < 0.05) (Fig. 1a, b, c) while substantially increased at 24 hpi (P < 0.01). The gene discussed is IFIH1; the disease is infection.