Classical swine fever virus genotype 2.1 triggers stronger inflammatory and immune responses in porcine alveolar macrophages than genotype 3.4

Abstract

Classical swine fever (CSF), caused by classical swine fever virus (CSFV), is a highly contagious disease characterized by immunosuppression. Since 1996, a shift from CSFV genotype 3.4 (G3.4) to genotype 2.1 (G2.1) has been observed in Taiwan. Although G2.1 exhibits higher replication efficiency than G3.4, their differential immune regulatory mechanisms remain unclear. This study investigated the responses of porcine alveolar macrophages (PAMs) infected with G2.1 versus G3.4, regarding their infection rates, cytokine protein levels, and transcriptomic profiling performed by RNA-seq with qPCR validation. G2.1 showed a significantly higher infection rate at 1 day post-infection (dpi) and induced stronger pro-inflammatory responses, including elevated IL-18 (1–3 dpi) and TNF-α (2 dpi) levels. Transcriptomic analysis revealed that G2.1 enriched immune pathways, such as JAK-STAT signaling, which favor Th17 cell differentiation. In contrast, G3.4 favors IL-17 signaling and apoptotic pathways, which are associated with B-cell recruitment, potentially promoting faster viral clearance. These findings reveal that while both CSFV genotypes engage the Th17 axis, G2.1 drives upstream differentiation to establish a pro-inflammatory niche, whereas G3.4 engages terminal IL-17 responses conducive to immune resolution. This study provides new insight into genotype-specific host responses that may contribute to the CSFV genotype shift observed in the field.