Cryptotanshinone protects porcine alveolar macrophages from infection with porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome (PRRS), caused by PRRS virus (PRRSV) infection, imposes enormous economic impact to the world pork industry. Currently there is no effective treatment to prevent PRRSV infection in swine. We report that the natural compound cryptotanshinone (Cpt) effectively inhibits the infection of various strains of PRRSV to porcine alveolar macrophages (PAMs), the primary cell target of PRRSV in vivo. Mechanistically, Cpt inhibits the activation of signal transducer and activator of transcription 3 (STAT3), and blocks the interleukin 10 (IL-10) stimulated as well as the basal level CD163 expression in PAMs. Cpt-treatment of PAMs is effective when applied either before or after PRRSV infection, with the combined pre- and post-PRRSV infection treatment resulting in the most significant, dose-dependent inhibition of PRRSV infection. Cpt inhibited both type I/II PRRSV infection in PAMs. Our study identified a new approach to prevent/treat PRRSV infection of pigs with natural compounds.