Outer membrane vesicles of Glaesserlla parasuis activate the endosomal cGAS-STING-IRF3 pathway through nucleic acid payload delivery: a biological perspective on host defense protocol optimization.

Glaesserlla parasuis (G. parasuis), a Gram-negative pathogen responsible for Glässer's disease, employs outer membrane vesicles (OMVs) as sophisticated nanoscale effectors to modulate host‒pathogen interplay. While bacterial OMVs are recognized as critical mediators of virulence dissemination, their functional orchestration in G. parasuis immunopathogenesis remains unclear. To date, few reports have focused on the relationships among G. parasuis, OMVs and host-susceptible cells; thus, more evidence is urgently needed to explore their crosstalk further. This study revealed a novel immune activation paradigm: both G. parasuis and its OMVs trigger robust type I interferon (IFN) responses via a DNA-sensing cascade. G. parasuis OMVs-Dio were internalized by macrophages in a time-dependent manner, partially via clathrin-mediated endocytosis but mainly via dynamin-dependent endocytosis. Studies have shown that IFNs play key antiviral roles in viral infections and important roles in bacterial infections. Our results suggested that IFNs inhibited G. parasuis adhesion and invasion of pulmonary alveolar macrophage (PAM) cells. Furthermore, by assessing the major components of OMVs, we confirmed that the DNA of G. parasuis, which is carried by OMVs, is the key component that induces the production of IFN in macrophages. The cGAS-STING-IRF3 pathway links the host's recognition of G. parasuis OMVs to IFN production. Taken together, our data reveal that G. parasuis OMVs activate cGAS/STING/IRF3 signaling and induce IFN production, which then affects the adhesion and invasion of G. parasuis. The discovery of this vesicle-mediated nucleic acid delivery system redefines the pathogenesis framework for G. parasuis and provides a trans-species conceptual advance in understanding how Gram-negative pathogens exploit vesicular trafficking to manipulate host immunity.