Extracellular vesicles of the probiotic E. coli O83 activate innate immunity and prevent allergy in mice

Abstract E. coli O83 (Colinfant Newborn) is a Gram-negative probiotic bacterium used in the clinic. When administered orally, it reduces allergic sensitisation but not allergic asthma. Intranasal administration may be more effective as it reaches the lungs directly. Gram-negative bacteria release outer membrane vesicles (OMVs) to communicate with the environment. Here we investigate whether intranasally administered E. coli O83 OMVs (EcO83-OMVs) can reduce allergy in mice. EcO83-OMVs were isolated by ultracentrifugation and characterised for their number, morphology (shape and size), composition (proteins and lipopolysaccharide), recognition by innate receptors (using transfected HEK293 cells) and immunomodulatory potential (in naïve splenocytes and bone marrow-derived dendritic cells). Their allergy-preventive effect was investigated in a mouse model of allergic airway inflammation. EcO83-OMVs are spherical nanoparticles with a size of about 110 nm. They contain lipopolysaccharide and protein cargo. We identified a total of 1120 proteins, 136 of which were enriched in OMVs compared to the parent bacteria. Proteins from the flagellum dominated. OMVs activated the pattern recognition receptors TLR2/4/5 as well as NOD1 and NOD2. EcO83-OMVs were internalised by epithelial cells and induced the production of pro- and anti-inflammatory cytokines in splenocytes and bone marrow-derived dendritic cells. Intranasal administration of EcO83-OMVs inhibited airway hyperresponsiveness, decreased airway eosinophilia, Th2 cytokine production and mucus secretion. We show for the first time that intranasally administered OMVs from probiotic Gram-negative bacteria have an anti-allergic effect. Our study highlights the advantages of OMVs as a safe platform for the prophylactic treatment of allergies.