Antiviral activity of tannic acid against porcine reproductive and respiratory syndrome virus and transcriptomic identification of TNFAIP3 as a candidate proviral host factor.

Porcine reproductive and respiratory syndrome virus (PRRSV) causes enormous economic losses to the global swine industry. Given the extensive viral diversity and the limited heterologous cross-protection of current vaccines, antiviral strategies with broad activity against diverse PRRSV strains are urgently needed. This study investigated the anti-PRRSV activity of tannic acid (TA), a plant-derived polyphenol. TA potently inhibited PRRSV replication in both MARC-145 cells (half-maximal inhibitory concentration [IC50] = 5.34 μM; selectivity index [SI] = 12.59) and primary porcine alveolar macrophages (IC50 = 4.22 μM; SI = 42.65) and exhibited broad activity against multiple lineages of PRRSV-2. Mode-of-action assays revealed that TA primarily exerts virucidal and post-entry inhibitory effects. RNA sequencing-based transcriptomic analysis of TA-treated, PRRSV-infected cells identified differentially expressed genes significantly enriched in the mitogen-activated protein kinase (MAPK), tumor necrosis factor (TNF), and interleukin-17 (IL-17) signaling pathways. Among five candidate genes selected for small interfering RNA (siRNA)-mediated functional validation, knockdown of TNF alpha-induced protein 3 (TNFAIP3, also known as A20) most significantly suppressed PRRSV replication. PRRSV infection markedly upregulated TNFAIP3 expression, and TA reversed this upregulation in a dose-dependent manner. TNFAIP3 silencing reduced viral RNA levels, nucleocapsid (N) protein expression, and infectious titers, with the most pronounced effect during early infection. Collectively, the findings identify TA as a potent anti-PRRSV polyphenol and reveal TNFAIP3 as a candidate proviral host factor that is upregulated during PRRSV infection, providing insights into virus-host interactions and potential targets for host-directed antiviral strategies.