Potential role of bacterial extracellular vesicles in the pathophysiology of systemic lupus erythematosus

Systemic Lupus Erythematosus (SLE) is a rare autoimmune disorder influenced by various factors, including infections. Following bacterial or viral infections, there is an increase in IFN-I production, primarily by plasmacytoid dendritic cells (pDCs). Overproduction of IFN-I has been shown to drive the progression of SLE. Recent findings indicate that the gene expression signature of IFN-I in lupus nephritis patients does not co-occur with pDCs as expected; instead, it is localized in glomerular regions with anastomosing capillaries, suggesting a potential source from the blood. T cells, natural killer cells, and myeloid lineage cells may also secrete IFN in the bloodstream. Bacterial presence in the bloodstream challenges the concept of blood sterility, raising the possibility that cell-free microbial components, such as bacterial extracellular vesicles (BEVs), could trigger excessive IFN production through systemic circulation. While existing studies suggest a role for BEVs in human SLE, experimental evidence has yet to establish a direct association between the entire BEV nanoparticle and the disease. Research has primarily focused on (1) mammalian EVs and (2) purified eDNA and other specific cargoes as contributors to SLE progression. It remains unproven whether these bacterial molecules exert their effects while associated with vesicular membranes, i.e., BEVs. We hypothesize that BEVs, which carry diverse cargoes including nucleic acids, may enter systemic circulation, induce cellular responses leading to IFN overproduction, and exacerbate SLE severity. Clinical studies could investigate the association of BEVs with SLE progression by monitoring their presence and quantity in blood samples and correlating these factors with disease outcomes. Furthermore, understanding the involvement of BEVs may aid in identifying SLE biomarkers, inform infection prevention strategies, and inspire the development of BEV-neutralizing agents.