MYH9 and infection: To investigate whether the activation of let-7f-5p affects PRRSV replication through targeting of the MYH9 gene, PAMs were transfected with increasing concentrations of let-7f-5p mimics (20, 50, 100 nM) or NC mimics (100 nM), followed by infection with the GD-HD strain at an MOI of 0.01.