Divergent immunometabolic landscapes of chicken and swan goose identify SERPINF2 as a novel restriction factor for influenza A virus

As the natural hosts of avian influenza virus (AIV), wild birds generally exhibit a more tolerant immune response to AIV infection compared to domestic poultry. However, the underlying mechanisms remain incompletely understood, partly due to limited access to wildlife biological samples imposed by animal protection principles. To investigate these differential immune responses, we established a peripheral blood mononuclear cells (PBMCs) infection platform. PBMCs from domestic chickens and swan geese were infected with H9N2 AIV, and label-free quantitative comparative proteomics was performed to identify differentially expressed proteins (DEPs) between the two species, aiming to uncover potential host antiviral factors. Proteomic analysis revealed that chicken PBMCs showed marked activation of antiviral defense and inflammatory pathways, accompanied by upregulation of oxidative stress-related pathways. In contrast, swan goose PBMCs predominantly activated pathways associated with cellular integrity maintenance, metabolic homeostasis, and RNA surveillance. Subsequently, 12 DEP candidates with high expression fold-changes in swan goose PBMCs were selected and expressed in DF-1 cells to evaluate their antiviral activities. Among these, only SERPINF2, a member of the serine protease inhibitor family, significantly inhibited H9N2 AIV replication in DF-1 cells. Mechanistically, SERPINF2 suppressed viral replication by specifically inhibiting the cleavage of the viral hemagglutinin (HA) protein, thereby reducing the production of infectious progeny virions. This study reveals distinct immune response patterns to H9N2 AIV infection in chickens and swan geese, and identifies SERPINF2 as a novel restriction factor against H9N2 AIV, providing new insights into the antiviral mechanisms in natural AIV hosts.