Membrane Vesicles of a Bacterial Mutualist Mediate Immune Regulation via Dendritic Cells. Mus musculus

Microbial molecules have evolved to promote transient and/or permanent associations with mammals. Although numerous examples of secretion systems employed by pathogens have been described, mechanisms by which commensal bacteria export molecules during symbiosis remain unknown. The human gut mutualist Bacteroides fragilis produces a capsular polysaccharide (PSA) that directs host immune development. We reveal herein that outer membrane vesicles (OMVs) deliver PSA to dendritic cells (DCs), promoting regulatory T cells and inducing anti-inflammatory cytokines during protection from intestinal disease. In addition, we found that TLR2 signaling by DCs is required for OMV sensing. Following internalization into DCs and engagement of TLR2, OMVs initiate a gene expression program that results in IL-10 production by DCs. Although it is known that the outcome of PSA sensing by the immune system is Treg induction, nothing is known about the intracellular signaling pathway(s) activated by PSA within DCs. We analyzed the gene expression profile of DCs treated with OMVs to uncover factors that are expressed in a PSA-dependent, TLR2-dependent manner. Our findings demonstrate DC-induced protection from disease via OMV-delivery of a beneficial microbial molecule, uncovering a novel paradigm for inter-kingdom communication between the microbiota and mammals. Overall design: RNA samples (1ug total RNA) from BMDCs were labeled with fluorescent dyes using the Quick Amp Labeling Kit (Agilent). Microarray (AgilentWhole Mouse Genome chip) hybridizations (65°C for 16 hours) and washes were performed with Agilent reagents following standard protocols. Microarrays were analyzed using an Agilent DNA Microarray Scanner G2565CA, and data were acquired using Agilent's Feature Extraction Software version 10.1.1.1. Significant genes were selected based on p2.0.