title: Extracellular vesicles modulate host-microbe responses by altering TLR2 activity and phagocytosis.
abstract: Oral delivery of Gram positive bacteria, often derived from the genera Lactobacillus or Bifidobacterium, can modulate immune function. Although the exact mechanisms remain unclear, immunomodulatory effects may be elicited through the direct interaction of these bacteria with the intestinal epithelium or resident dendritic cell (DC) populations. We analyzed the immune activation properties of Lactobacilli and Bifidobacterium species and made the surprising observation that cellular responses in vitro were differentially influenced by the presence of serum, specifically the extracellular vesicle (EV) fraction. In contrast to the tested Lactobacilli species, tested Bifidobacterium species induce TLR2/6 activity which is inhibited by the presence of EVs. Using specific TLR ligands, EVs were found to enhance cellular TLR2/1 and TLR4 responses while TLR2/6 responses were suppressed. No effect could be observed on cellular TLR5 responses. We determined that EVs play a role in bacterial aggregation, suggesting that EVs interact with bacterial surfaces. EVs were found to slightly enhance DC phagocytosis of Bifidobacterium breve whereas phagocytosis of Lactobacillus rhamnosus was virtually absent upon serum EV depletion. DC uptake of a non-microbial substance (dextran) was not affected by the different serum fractions suggesting that EVs do not interfere with DC phagocytic capacity but rather modify the DC-microbe interaction. Depending on the microbe, combined effects of EVs on TLR activity and phagocytosis result in a differential proinflammatory DC cytokine release. Overall, these data suggest that EVs play a yet unrecognized role in host-microbe responses, not by interfering in recipient cellular responses but via attachment to, or scavenging of, microbe-associated molecular patterns. EVs can be found in any tissue or bodily fluid, therefore insights into EV-microbe interactions are important in understanding the mechanism of action of potential probiotics and gut immune homeostasis.
authors.affiliation: Nutricia Research, Utrecht, The Netherlands ; Department of Pharmacology, Utrecht Institute for Pharmaceutical Sciences, Utrecht University, Utrecht, The Netherlands.
authors.forename: Jeroen
authors.initials: J
authors.lastname: van Bergenhenegouwen
authors.affiliation: Department of Pharmacology, Utrecht Institute for Pharmaceutical Sciences, Utrecht University, Utrecht, The Netherlands.
authors.forename: Aletta D
authors.initials: AD
authors.lastname: Kraneveld
authors.affiliation: Nutricia Research, Utrecht, The Netherlands.
authors.forename: Lieke
authors.initials: L
authors.lastname: Rutten
authors.affiliation: Nutricia Research, Utrecht, The Netherlands.
authors.forename: Nienke
authors.initials: N
authors.lastname: Kettelarij
authors.affiliation: Nutricia Research, Utrecht, The Netherlands ; Department of Pharmacology, Utrecht Institute for Pharmaceutical Sciences, Utrecht University, Utrecht, The Netherlands.
authors.forename: Johan
authors.initials: J
authors.lastname: Garssen
authors.affiliation: Nutricia Research, Utrecht, The Netherlands ; Department of Pharmacology, Utrecht Institute for Pharmaceutical Sciences, Utrecht University, Utrecht, The Netherlands.
authors.forename: Arjan P
authors.initials: AP
authors.lastname: Vos
mesh_terms: D000818:Animals; D001644:Bifidobacterium / Q000378:metabolism / Q000502:physiology*; D016207:Cytokines / Q000378:metabolism; D003713:Dendritic Cells / Q000276:immunology / Q000378:metabolism; D057809:HEK293 Cells; D054884:Host-Pathogen Interactions; D006801:Humans; D019344:Lactic Acid / Q000096:biosynthesis; D051379:Mice; D010587:Phagocytosis; D013045:Species Specificity; D051195:Toll-Like Receptor 2 / Q000378:metabolism*; D051216:Toll-Like Receptor 6 / Q000378:metabolism; D022161:Transport Vesicles / Q000276:immunology / Q000378:metabolism* / Q000382:microbiology
chemical_list: D016207:Cytokines; C495369:Tlr6 protein, mouse; D051195:Toll-Like Receptor 2; D051216:Toll-Like Receptor 6; D019344:Lactic Acid