Cloning, characterization and comparative innate immune functions of duRIPK2 in Cherry Valley duck against APEC and NDRV

Receptor-interacting protein kinase 2 (RIPK2) is an indispensable adaptor and effector protein in the NOD-like receptor (NLRs) signaling pathway. Its C-terminal CARD binds NLRs via CARD-CARD interaction, while its N-terminal kinase domain (KD) mediates ubiquitination and phosphorylation for downstream signaling. In this study, we cloned and analyzed the gene sequence and structural characteristics of Cherry Valley duck RIPK2 ( du RIPK2), systematically investigated its expression distribution in different tissues of Cherry Valley ducks, and explored its immune regulatory role in the infection of avian pathogenic Escherichia coli (APEC) and novel duck reovirus (NDRV). Through bioinformatics analysis, the full-length open reading frame (ORF) of du RIPK2 was identified for the first time, and conserved sites related to its kinase role were predicted. The tissue expression profile analysis indicated that du RIPK2 was highly expressed in the liver, muscle, and trachea, but was expressed at a lower level in intestinal tissues. The infection model analysis confirmed that APEC infection could markedly elevate du RIPK2 expression level, induce the enhanced expression of inflammatory factors, and inhibit the bacterial load. Whereas, in NDRV infection, the expression of du RIPK2 was significantly inhibited, accompanied by the increased expression of inflammatory factors, and the viral load remained at a relatively high level at 3dpi. The results demonstrate that du RIPK2 is a momentous hub of both anti-bacterial and anti-viral immunity systems in ducks, advancing the mechanistic understanding of the NOD-RIPK2 signaling pathways in poultry, providing direction for breeding strategies and entry points for adjuvant development, and reducing antibacterial and antiviral drug dependency in the duck farming industry.