Investigating the Immunomodulatory Impact of Fecal Bacterial Membrane Vesicles and Their IgA Coating Patterns in Crohn's Disease Patients.

The human intestinal tract contains trillions of bacteria that coexist in a symbiotic relationship with human cells. Imbalances in this interaction can lead to disorders such as Crohn's disease (CD). Bacteria membrane vesicles (MVs), which are released by almost all bacteria, have been demonstrated to play a crucial role in bacteria-host interactions. In this study, we assessed the physical characterizations, immunomodulatory effects, and IgA interactions of MVs derived from fecal samples of CD patients and healthy controls (HCs). MVs were isolated from the frozen fecal samples using a combination of ultrafiltration and size-exclusion chromatography. Using nanoparticle tracking analysis, we found that the MVs of the CD patients showed a significantly lower concentration compared to those of the HCs. Cryo-transmission electron microscopy revealed the larger size of the MVs in active CD (Ac-CD) compared to the MVs of remission CD (Re-CD) and HCs. Differentiated monocyte THP-1 cells released more TNF-a when exposed to MVs from the HCs compared to the CD patients. On the other hand, the MVs from the HCs and Re-CD patients but not the Ac-CD patients induced more anti-inflammatory IL-10. Intriguingly, bead-based flow cytometry analysis showed that the MVs of the HCs and Re-CD patients were more coated with IgA compared to those of the Ac-CD patients. These results suggest the potential role of MVs in the immunomodulatory impact on the pathophysiology of CD. Moreover, IgA seems to regulate these effects by direct binding, which was not the case for the Ac-CD patients. Finally, the IgA coating patterns of the MVs could be used as an additional disease biomarker, as they can clearly identify the exacerbation status of CD.