Background:Our previous study showed that 3 plant extracts enhanced the immune responses and growth efficiency of weaned pigs infected with porcine reproductive and respiratory syndrome virus (PRRSV), which is one of the most economically important disease in swine industry. However, each plant extract differently effected on growth efficiency and immune responses. Therefore, the objective of this study was conducted to characterize the effects and investigate the potential underlying mechanisms of 3 plant extracts on gene expression of alveolar macrophages in weaned pigs experimentally infected with PRRSV. Results:PRRSV infection altered (P<0.05) the expression of 1,352 genes in pigs fed the control (CON;755 up, 597 down). Compared with the infected CON, feeding capsicum (CAP), garlic botanical (GAR), or turmeric oleoresin (TUR) altered the expression of 46 genes (24 up, 22 down), 134 genes (59 up, 75 down), or 98 genes (55 up, 43 down) in alveolar macrophages of PRRSV-infected pigs, respectively. PRRSV infection up-regulated (P<0.05) the expression of genes related to cell apoptosis, immune system process, and response to stimulus, but down-regulated (P<0.05) the expression of genes involved in signaling transduction and innate immune response. Compared with the infected CON, feeding TUR or GAR reduced (P<0.05) the expression of genes associated with antigen processing and presentation, feeding CAP up-regulated (P<0.05) the expression of genes involved in antigen processing and presentation. Supplementation of CAP, GAR, or TUR also enhanced (P<0.05) the expression of several genes related to amino acid metabolism, steroid hormone synthesis, or RNA degradation, respectively. Conclusions:The results suggest that 3 plant extracts differently regulated the expression of genes in alveolar macrophages of PRRSV-infected pigs, especially altering genes involved in immunity.