Helicobacter pylori colonises the stomach of more than 3 billion people worldwide, resulting in a variety of symptoms including chronic inflammation, gastric ulcers and gastric cancer. Although H. pylori strains harbouring the type 4 secretion system (T4SS) are associated with more severe pathology, strains that lack the T4SS are still capable of inducing inflammation, suggesting that there are other mechanisms whereby H. pylori initiates pathology in the host. We recently identified that peptidoglycan-containing bacterial outer membrane vesicles (OMVs) produced by all H. pylori strains initiate pro-inflammatory innate and adaptive immune responses, ultimately contributing to pathology in the host.

OMVs are spherical, bi-layered membrane nano-structures ranging from 20 to 300 nm in size and are produced by all Gram-negative pathogens as part of their normal growth. We reported that H. pylori OMVs enter human epithelial cells via lipid rafts and are subsequently detected by the host pathogen recognition receptor, nucleotide oligomerization domain 1 (NOD1) that recognises Gram-negative bacterial peptidoglycan (PG). The recognition of PG-containing H. pylori OMVs by NOD1 resulted in the development of autophagy and pro-inflammatory IL-8 responses. Using fluorescent lifetime imaging microscopy (FLIM)-fluorescence energy transfer (FRET), we revealed that once within host epithelial cells, OMVs migrate to early endosomes where they interact with NOD1 and facilitate the development of NOD1-dependent autophagy and inflammatory responses. Moreover, we found that the degradation of OMVs via NOD1-dependent autophagy enabled the packaging of OMV proteins into host-cell derived exosomes. We identified that these OMV-containing exosomes were capable of being presented to T cells via antigen presenting cells, resulting in the generation of H. pylori-specific adaptive immune responses. Collectively, our findings identify Gram-negative bacterial OMVs as a mechanism whereby pathogens such as H. pylori initiate innate immune responses at host mucosal surfaces, and provide a method for the establishment of pathogen-specific adaptive immunity in vivo.