E. coli A0 34/86 (serotype O83:K24:H31; E. coli O83) is a probiotic bacterial strain that is commercially available as an oral live vaccine and used to treat nosocomial infections and diarrhoea in infants. We have shown that intranasal application of E. coli O83 suppressed ovalbumin (OVA)-induced allergic airway inflammation in mice in a prophylactic and therapeutic setting, but the microbial factors that mediate these effects remain to be investigated.

In this study, we isolated E. coli O83 outer membrane vesicles (EcO83-OMVs) by ultracentrifugation and tested them for their effect on the immune system in vitro and in vivo.

EcO83-OMVs stimulated production of IL-8 in the human intestinal cell line HT-29. When co-cultured with splenocytes derived from naïve mice, EcO83-OMVs induced secretion of IL-6, IL-10, TNF-α and IFN-γ in a dose-dependent manner.

Furthermore, we asked whether vesicles, similarly to the whole bacteria, have a beneficial effect on allergy. BALB/c mice were sensitized and challenged with OVA, and before each application, they received either 100 ng or 1 µg of EcO83-OMVs intranasally. EcO83-OMVs-treated mice exhibited reduced airway hyperreactivity, as measured by the whole-body plethysmography, and reduced airway eosinophilia compared to the controls.

Thus we show that outer membrane vesicles (OMVs) produced by probiotic bacteria communicate with and modulate the immune responses in the host. The exact mechanism of cellular uptake of OMVs and the activating signalling events in the host cells will be further investigated.