BACKGROUND: Following allergen exposure, cytokines and other pro-inflammatory signals play an important role in the immunological cascade leading to allergic sensitization. Inflammasomes sense exogenous and endogenous danger signals and trigger IL-1β and IL-18 activation which in turn shape Th2 responses. Honey bee venom (BV) allergies are very common; however, the local inflammatory cascade leading to the initiation of allergic sensitization is poorly understood. In this study, the local inflammatory cascades in skin after exposure to BV were investigated. METHODS: The mechanisms of inflammasome activation in human skin and in cultured keratinocytes upon BV exposure were analyzed by ELISA, Western blot, flow cytometry, siRNA techniques, and immunofluorescence. RESULTS: In an ex vivo bee sting model, BV induced IL-1β release suggesting the activation of inflammasomes. Indeed, in cultured keratinocytes, the BV component melittin triggered IL-1β and IL-18 release via the AIM2 inflammasome. AIM2 is a cytosolic DNA receptor, and mitochondrial as well as genomic DNA was detected in the cytosol of melittin-treated keratinocytes as triggers of inflammasome activation. As a mechanism, melittin mediated destruction of mitochondrial membranes leading to the leakage of mitochondrial DNA into the cytosolic compartment. CONCLUSION: These data suggest that upon BV exposure, keratinocytes are involved in an innate immune response by the activation of the AIM2 inflammasome and subsequent IL-1β and IL-18 release triggered by endogenous DNA. As IL-1β and IL-18 are involved in Th2- and IgE-mediated immune reactions, these results could add to the understanding of the role of the tissue microenvironment to subsequent allergic responses.
BACKGROUND: Following allergen exposure, cytokines and other pro-inflammatory signals play an important role in the immunological cascade leading to allergic sensitization. Inflammasomes sense exogenous and endogenous danger signals and trigger IL-1β and IL-18 activation which in turn shape Th2 responses. Honey bee venom (BV) allergies are very common; however, the local inflammatory cascade leading to the initiation of allergic sensitization is poorly understood. In this study, the local inflammatory cascades in skin after exposure to BV were investigated. METHODS: The mechanisms of inflammasome activation in human skin and in cultured keratinocytes upon BV exposure were analyzed by ELISA, Western blot, flow cytometry, siRNA techniques, and immunofluorescence. RESULTS: In an ex vivo bee sting model, BV induced IL-1β release suggesting the activation of inflammasomes. Indeed, in cultured keratinocytes, the BV component melittin triggered IL-1β and IL-18 release via the AIM2 inflammasome. AIM2 is a cytosolic DNA receptor, and mitochondrial as well as genomic DNA was detected in the cytosol of melittin-treated keratinocytes as triggers of inflammasome activation. As a mechanism, melittin mediated destruction of mitochondrial membranes leading to the leakage of mitochondrial DNA into the cytosolic compartment. CONCLUSION: These data suggest that upon BV exposure, keratinocytes are involved in an innate immune response by the activation of the AIM2 inflammasome and subsequent IL-1β and IL-18 release triggered by endogenous DNA. As IL-1β and IL-18 are involved in Th2- and IgE-mediated immune reactions, these results could add to the understanding of the role of the tissue microenvironment to subsequent allergic responses.
Authors: Karina F Zoccal; Carlos A Sorgi; Juliana I Hori; Francisco W G Paula-Silva; Eliane C Arantes; Carlos H Serezani; Dario S Zamboni; Lúcia H Faccioli Journal: Nat Commun Date: 2016-02-23 Impact factor: 14.919