Molecular mechanisms regulating the synergism between IL-32γ and NOD for the activation of eosinophils

IL-32 is a proinflammatory cytokine associated with infections, autoimmune diseases, and allergic asthma. In the present study, we elucidated the synergistic effect of IL-32γ and NOD ligand on the activation of human eosinophils, principal effector cells for allergic inflammation, and the underlying mechanisms. Specific IL-32-binding protein, PR3, was found to localize on the cell surface and in the cytoplasm of eosinophils. IL-32γ was more capable of activating eosinophils than its isotype variant IL-32α and exhibited synergistic effect with NOD1 ligand iE-DAP and NOD2 ligand MDP on the induction of allergic inflammation-related IL-1β, TNF-α, and chemokines CXCL8, CCL3, and CCL4 (P<0.05). Moreover, IL-32γ and iE-DAP or MDP induced the significant up-regulation of the cell-surface expression of adhesion molecule CD18 and ICAM-1 on eosinophils. Synergism between IL-32γ and NOD ligands was dependent on the activation of intracellular caspase 1, ERKs, p38 MAPK, and NF-κB pathways in eosinophils. The further-enhanced CD18 and ICAM-1 expression and production of cytokines and chemokines were observed in eosinophils cocultured with human bronchial epithelial BEAS-2B cells. Furthermore, combined treatment of IL-32γ and NOD ligand could activate the release of eosinophil extracellular DNA traps, thereby implying the pathogen-defense mechanisms of eosinophils. Together, the above study provides pivotal immunological mechanisms by which bacterial infection-mediated activation of NOD1,2, together with IL-32γ, can synergize the activation of eosinophils interacting with bronchial epithelial cells.