Proinflammatory role of blister fluid-derived exosomes in bullous pemphigoid

Bullous pemphigoid is an autoimmune inflammatory disorder characterized by the presence of autoantibodies against bullous pemphigoid autoantigens, leading to dermal-epidermal separation with consequent blister formation. However, whether and how the components of blister fluid exacerbate the progression of bullous pemphigoid is unclear. Exosomes are nanometre-sized vesicles released from cells into the body fluid, where they can transmit signals throughout the body. In the present study, we isolated and characterized exosomes from blister fluids of patients with bullous pemphigoid, evaluated their proinflammatory role, and identified the underlying molecular mechanisms. We found that exosomes isolated from blister fluids of patients with bullous pemphigoid showed the expected size and expressed the marker proteins CD63, CD81, and CD9. Additionally, blister fluid-derived exosomes were internalized by human primary keratinocytes, inducing the production of critical inflammatory cytokines and chemokines. Western blotting analysis showed robust and rapid activation of the extracellular signal-regulated kinase 1/2 and signal transducer and activator of transcription 3 signalling pathways in human primary keratinocytes after stimulation with blister fluid-derived exosomes. We also found that blister fluid-derived exosomes indirectly induced neutrophil trafficking by upregulating C-X-C motif chemokine ligand 8 in vitro. Furthermore, CD63 was localized mostly to keratinocytes and infiltrative granulocytes in skin lesions, suggesting that these cells were the possible sources of exosomes in blister fluid. Using mass spectrometry, we analysed the proteomes of blister fluid-derived exosomes and identified a variety of proteins implicated in inflammatory and immune responses. Together, our findings provide strong evidence that blister fluid-derived exosomes are involved in the local autoinflammatory responses of the skin associated with bullous pemphigoid. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.