Receptor for advanced glycation end products (RAGE) plays a role in inflammatory reactions. The soluble form of RAGE (sRAGE) acts as a decoy to inhibit interactions of RAGE with advanced glycation end products such as High mobility group box 1 (HMGB1). We have demonstrated that HMGB1 directs Th17 skewing by regulating dendritic cell (DC) functions in a previous study. However, the protective effects of HMGB1 blockade with sRAGE in the development of neutrophilic asthma remain unclear. Here, we showed that allergen challenge decreased expression of sRAGE in a murine model of neutrophilic asthma, correlating well with neutrophil counts and interleukin (IL)-17 production. When HMGB1 signalling was blocked by intratracheal administration of sRAGE before sensitisation, HMGB1 expression, neutrophilic inflammation, and Th17-type responses were reduced significantly. Anti-asthma effects of sRAGE were achieved by inhibition of RAGE and IL-23 expression in airway CD11c+ antigen-presenting cells. Finally, we showed that sRAGE inhibited Th17 polarisation induced by recombinant HMGB1 (rHMGB1)-activated dendritic cells (DCs) in vitro. Adoptive transfer of rHMGB1-activated DCs was sufficient to restore airway inflammation, whereas transfer of rHMGB1 plus sRAGE-activated DCs significantly reduced neutrophilic inflammation. Thus, sRAGE prevents Th17-mediated airway inflammation in neutrophilic asthma at least partly by blocking HMGB1/RAGE signalling in DCs.

We demonstrate that high mobility group box 1 protein (HMGB1) directs Th17 skewing by regulating dendritic cell (DC) function. First, our in vitro studies reveal that recombinant HMGB1 (rHMGB1) activates myeloid DCs to produce IL-23 in vitro, and rHMGB1-activated DCs prime naïve lymphocytes to produce the Th17 cytokine IL-17A. Second, we demonstrate that anti-HMGB1 neutralizing antibody attenuates HMGB1 expression, neutrophilic inflammation, airway hyperresponsiveness, and Th17-related cytokine secretion in vivo by using a murine model of neutrophilic asthma induced by ovalbumin (OVA) plus lipopolysaccharide (LPS). Furthermore, anti-HMGB1 neutralizing antibody decreases the number of Th17 cells in lung cells and suppresses the production of IL-23 by lung CD11C+ APCs. Finally, we show that intranasal adoptive transfer of rHMGB1-activated DCs was sufficient to restore lung neutrophilic inflammation and the Th17 response in a DC-driven model of asthma, whereas the transfer of rHMGB1 plus anti-HMGB1-treated mDCs significantly reduced these inflammation phenotypes. These data suggest, for the first time, that HMGB1 drives the DC-polarized Th17-type response in allergic lung inflammation and that blocking HMGB1 may benefit the attenuation of neutrophilic airway inflammation in asthma.

BackgroundVitamin D plays an important role in pulmonary resistance and immunity, and its deficiency has been linked to various respiratory infections. Little is known about the effect of vitamin D deficiency on host pulmonary defense to Aspergillus fumigatus (A. fumigatus).MethodsMice raised on vitamin D sufficient or deficient diets were infected intratracheally with A. fumigatus conidia. Mortality, fungal growth, weight loss and lung histology were monitored. Alveolar macrophages (AMs) were stimulated with A. fumigatus conidia in vitro. The kinetics of pro-inflammatory cytokines (TNF-α, IL-1β and IL-6), chemokines (CXCL1, CCL3), and pattern recognition receptors (Toll-like receptor [TLR] 2, TLR 4 and dectin-1) expression in the lungs and AMs were measured.ResultsUpon A. fumigatus infection, vitamin D deficient mice showed higher mortality, greater fungal load, and more weight loss than its sufficient counterparts. Vitamin D deficient mice demonstrated aggravated and prolonged histological evidence of lung inflammation as well as enhanced BAL cell counts, dominated by neutrophils after A. fumigatus inoculation. Increased basal levels of pro-inflammatory cytokines in the lungs and AMs from naïve vitamin D deficient mice were observed. Upon A. fumigatus exposure, vitamin D deficiency led to enhanced and sustained expression of TNF-α, IL-1β, IL-6, CXCL1 and CCL3 both in vivo and in vitro. Up-regulation of TLR2, TLR4 and dectin-1was observed in the lungs and AMs from vitamin D deficient mice both at baseline and after A. fumigatus exposure.ConclusionsVitamin D deficiency causes defective pulmonary resistance to A. fumigatus in mice, possibly by the enhanced basal expression of pattern recognition receptors and pro-inflammatory cytokines, which induced excessive inflammatory response in response to A. fumigatus challenge.