Distribution and Regulation of RIG-I in Porcine Intestine During TGEV and PDCoV Infection

Transmissible gastroenteritis virus (TGEV) and porcine deltacoronavirus (PDCoV) are major enteric coronaviruses responsible for severe diarrhea in neonatal piglets. Retinoic acid-inducible gene I (RIG-I) is a key sensor against RNA viruses, yet its distribution in the porcine intestine and regulatory roles during TGEV and PDCoV infections remain insufficiently understood. In this study, we show that under normal conditions, RIG-I predominantly localizes in lamina propria antigen-presenting cells, with its expression increasing with age. Following viral infection in vivo and in vitro, both TGEV and PDCoV induce RIG-I expression, although TGEV elicits a more robust activation of RIG-I and downstream interferon pathways. Mechanistically, RIG-I overexpression inhibits replication of both viruses, whereas RIG-I knockdown significantly enhances TGEV proliferation only, implying that TGEV primarily depends on RIG-I–mediated immune responses, while PDCoV may rely on other pattern recognition receptors (PRRs). These findings unveil distinct immune regulatory strategies of TGEV and PDCoV and highlight the central role of RIG-I in controlling TGEV infection, offering a theoretical foundation for targeted preventive and therapeutic interventions.