AGR2-mediated cell-cell communication controls the antiviral immune response by promoting the thiol oxidation of TRAF3.

Protein disulfide isomerases (PDIs) are essential catalysts for the formation and isomerization of disulfide bonds in diverse substrate proteins and exert multiple functions under pathophysiological conditions. Here, we show that anterior gradient 2 (AGR2), a member of PDIs, acts as a negative regulator in antiviral immunity. RNA virus infection stimulated the expression and secretion of AGR2 in epithelial cells. While AGR2 is absent in immune cells, both intracellular AGR2 and extracellular AGR2 compromised type I interferon (IFN-I) production in vitro and in vivo. The inhibitory effect of secreted AGR2 on the immune response resulted from its crosstalk with immune cells, such as macrophages, by which eAGR2 was internalized via endocytosis depending on its adhesion motif. We further identified AGR2 as a novel binding protein of TRAF3, which forms a disulfide bond between Cys81 of AGR2 and Cys296 on TRAF3. This interaction led to the inhibition of TRAF3 K63-linked ubiquitination and TRAF3-TBK1 complex formation, ultimately impairing TRAF3's ability to induce IFN-I production. The TRAF3 Cys296 mutation diminishes oxidative modification by AGR2 but enhances self-association of TRAF3 and IFN-I production. Our study demonstrated a cysteine-dependent oxidative modification of TRAF3 by AGR2 that suppresses TRAF3 activity and maintains innate immune homeostasis.