Exosomes -: nanovesicles with possible roles in allergic inflammation

Exosomes are nano-sized membrane vesicles which are released extracellularly after fusion of multivesicular endosomes with the cell membrane. Despite their characteristic composition of proteins compared to the cell membrane, no exosome-specific molecule has so far been characterized. Exosomes are found in bronchoalveolar lavage (BAL), urine, serum and breast milk, and are released from several cells implicated in allergy including mast cells, dendritic cells (DC), T cells and epithelial cells. Antigen-loaded exosomes have been shown to be highly immunogenic and we propose that exosomes could be a modulating factor in allergic responses. Allergen-presenting exosomes could transport allergen and stimulate allergen-specific T cells, and possibly also biasing T cell responses depending on the molecules present on the exosome surface. Furthermore, exosomes from mast cells, highly active in allergic reactions, have been found to induce DC maturation and also to be able to transport functional RNA to recipient cells, suggesting a new pathway for cell communication. Reversely, tolerizing exosomes e.g. tolerosomes, from gut or breast milk, could block an allergic response or prevent allergy development. A better understanding of the role of exosomes in allergies could make us understand how allergy can be prevented or lead to the development of more efficient treatments.