Extracellular vesicles of the Gram-positive gut symbiont Bifidobacterium longum induce immune-modulatory, anti-inflammatory effects

The gut microbiota is now well known to affect the host's immune system. One way of bacterial communication with host cells is via the secretion of vesicles, small membrane structures containing various cargo. Research on vesicles secreted by Gram-positive gut bacteria, their mechanisms of interaction with the host and their immune-modulatory effects are still relatively scarce. Here we characterized the size, protein content, and immune-modulatory effects of extracellular vesicles (EVs) secreted by a newly sequenced Gram-positive human gut symbiont strain - Bifidobacterium longum AO44. We found that B. longum EVs exert anti-inflammatory effects, inducing IL-10 secretion from both splenocytes and dendritic cells (DC)-CD4+ T cells co-cultures. Furthermore, the EVs protein content showed enrichment in ABC transporters, quorum sensing proteins, and extracellular solute-binding proteins, which were previously shown to have a prominent function in the anti-inflammatory effect of other strains of B. longum. This study underlines the importance of bacterial vesicles in facilitating the gut bacterial immune-modulatory effects on the host and sheds light on bacterial vesicles as future therapeutics.

Automated summary

This study examined the extracellular vesicles (EVs) secreted by a newly sequenced Gram-positive human gut symbiont strain, Bifidobacterium longum AO44. The EVs were found to have anti-inflammatory effects, inducing the secretion of IL-10 from splenocytes and dendritic cells (DC)-CD4+ T cells co-cultures. The protein content of the EVs was enriched in ABC transporters, quorum sensing proteins, and extracellular solute-binding proteins, which are known to play a significant role in the anti-inflammatory effects of other strains of B. longum. This study highlights the importance of bacterial vesicles in modulating the host immune system and suggests their potential as future therapeutics.