All Gram negative bacteria naturally produce extracellular outer membrane vesicles (OMVs) as part of their normal growth process. Bacterial OMVs range from approximately 20-300nm in size and contain many of the components present within their parent bacterium including proteins, DNA and peptidoglycan.
Our research primarily focuses on understanding pathogenesis mediated by bacterial OMVs. Our findings have identified the ability of bacterial OMVs to enter human epithelial cells via lipid rafts. Upon entry into host epithelial cells, peptidoglycan-containing OMVs are detected by the cytosolic host pathogen recognition molecule nucleotide oligomerization domain 1 (NOD1), resulting in the development of OMV-specific innate and humoral immune responses.
More recently, we have examined the mechanisms of OMV recognition by NOD1, and their subsequent intracellular fate, in order to further understand their role in bacterial pathogenesis. Using confocal microscopy and live cell imaging, we determined that the recognition of PG-containing 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. Collectively, our findings identify Gram-negative bacterial OMVs as a mechanism whereby pathogens irrespective of their mode of infection can initiate innate immune responses at host mucosal surfaces, in addition to providing a method for the establishment of pathogen-specific adaptive immunity in vivo.