Furthermore, we identified the miRNomes pre- and post-infection with PRRSV strain LS-4 and concluded that ssc-miR-30d-R_1 targeted Toll-like receptor 4 (TLR4) of MARC-145 cells to suppress the production of immune cytokines by inhibiting the TLR4/MyD88/NF-κB pathway both in vitro and in vivo. This evidence concerns the gene TLR4 and infection.