Studies on Staphylococcus aureus derived extracellular vesicle as one of causes in immune-based inflammatory disorder in the lung

Abstract

Asthma is characterized by the over-whelming activation of the adaptive immune system against allergens and is caused by common allergens including house dust mite and pollen to invade in to the airway. The Th2 hypothesis of asthma is that exaggerated Th2 immune response in allergen sensitized person induces eosinophilic airway inflammation in combination with a decreased Th1 response. Although many reports support the Th2 hypothesis, recent researches reported that IFN-γ (a Th1 cytokine) is elevated in the blood and airway, and IL-17 (a Th17 cytokine) is also increased in asthma patients, especially severe asthma patients (neutrophilic asthma). Previously, our group first found that house dust, an important causative agent, induces lung inflammation derived by T helper cell (Th) 17 immune response and house dust-derived extracellular vesicles (dust EV) also induce lung inflammation mediated by Th17 immune response. We also found that house dust contaminates S. aureus which is gram-positive bacterium presenting in air or indoor dust as well as colonizing the human skin and nasopharynx. S. aureus is a one of the most important human pathogens, and it causes various superficial, systemic, and nosocomial infections. There are no researches that reported relationship between S. aureus-derived inflammatory lung diseases and Th17 immune response. Recent studies reported that S. aureus can produce S. aureus-derived vesicles that may be able to act as causative agent for inflammation such as atopic dermatitis.The vesicles were prepared by sequential ultrafiltration and ultracentrifugation. In vitro and in vivo innate immune dysfunction was evaluated after application to alveolar macrophages in vitro and after once application to the mouse airways, respectively. Adaptive immune dysfunction was evaluated after 3 weeks airway exposure of the vesicles with or without ovalbumin (OVA), respectively. Inflammation and immune response were evaluated at 6 h or 48 h after the final application. Inflammatory cytokines and serum antibody were measured by ELISA and flow cytometry. Else, evaluation of inflammation was measured by histology stained with H&E. The present study shows that S. aureus-derived vesicles enhanced the production of proinflammatory mediators, such as TNF-alpha, IL-6 and IP-10, from alveolar macrophages. In addition, once application of the vesicles into the mouse airways increased lung inflammation and the production of IL-12 and IL-6 (Th1 and Th17 polarizing cytokines, respectively) as well as proinflammatory mediators including TNF-alpha and IL-1. Repeated airway exposure of the vesicles for 3 weeks induced neutrophilic inflammation in the lung, which is associated with both Th1 and Th17 cell responses. In terms of adjuvant effect of the vesicles, sensitization with the vesicles and OVA and then challenge with OVA alone induced neutrophilic inflammation which is partially eliminated by the absence of IFN-gamma or IL-17. Our results indicate that S. aureus-derived vesicles can induce neutrophilic inflammation in the lung via both Th1- and Th17-dependent mechanisms. S. aureus-derived vesicles are a novel target for the development of technologies for neutrophilic asthma control.