Fig. 1

Bt OMVs stimulate production of immunoregulatory IL-10 from whole colonic biopsies and colonic LP DC. During normal anaerobic growth, Bt cells produce and release OMVs into the external milieu. a Electron microscope photograph of OMVs collected by sterile filtration of Bt culture supernatants through 0.22 μm membranes. Red arrows point to spherical nanostructures consisting of lipid bilayer. Scale bar, ~ 100 nm. Colonic biopsies taken from the rectosigmoid junction of healthy individuals were grown in a pIVOC system mucosal side up within Snapwell inserts for 6 h in IVOC medium with or without 10⁸-10⁹ Bt OMVs. b Following culture, biopsies were snap-frozen and cytokines and chemokines were measured within tissue lysates by LEGENDplex cytokine bead array. Amounts of MCP-1, IFN-γ, IL-8, IL-1β, IL-6, and IL-10 shown are mean ± SEM values from n = 4 healthy controls with two experimental replicates each. Statistical significance was determined using nonparametric Mann-Whitney U tests; *p < 0.05; **p < 0.01; ***p < 0.001. Five biopsies each from proximal and distal colon of healthy individuals were washed with DTT/EDTA and digested with collagenase/liberase to obtain total LP cells. Cells were then cultured for 20 h in the presence of either killed 10⁷ Bt/mL or 10¹⁰ Bt OMV/mL in complete RPMI medium, and mDC were examined by flow cytometry. c Identification of mDC within the total LP cells. d Mean fluorescence intensity of HLA-DR on total mDC in response to medium only, Bt or Bt OMVs. Statistical significance was determined by one-way ANOVA with Dunnett’s multiple comparisons test; *p < 0.05. e Proportion of mDC expressing IL-6 (top panel) and IL-10 (bottom panel) within the colonic LP. Pooled data from n = 6 HC. Statistical significance was determined using non-parametric Kruskal-Wallis ANOVA with Dunn’s multiple comparisons test; *p < 0.05