highly significantP-value < 0.001
P-value < 0.05 was considered as significant (*); P-value < 0.01 was considered as highly significant (**); P-value < 0.001 was considered as extremely significant (***); and ns represents no difference. 3 Results 3.1 Overexpression of PCV2 ORF5 activates the host inflammatory response Based on the results of our previous studies, miR-21 is a key regulator of PCV2 infection-induced inflammatory response.