Desert dust induces TLR signaling to trigger Th2-dominant lung allergic inflammation via a MyD88-dependent signaling pathway

Abstract Asian sand dust ( ASD) is known to exacerbateasthma, although its mechanism is not yet well understood. In this study, when the effects on inflammatory response by LPS present in ASDwas investigated by measuring the gene expression of cytokines and chemokines in RAW264.7 cells treated with ASDand/or polymyxin B(PMB), the ASDeffects were attenuated by PMB, but not completely. When an in vitro study was performed using bone marrow-derived macrophages(BMDMs) from WT, TLR2−/− , TLR4−/− , and MyD88 −/− BALB/c mice and BMDMs from WT, TLR2−/− , TLR4−/− , TLR2/4 −/− , TLR7/9 −/− , and MyD88 −/− C57BL/6J mice, cytokine (IL-6, IL-12) production in BMDMs was higher in ASD-stimulated TLR2−/− cells than in TLR4−/− cells, whereas it was lower or undetectable in TLR2/4 −/− and MyD88 −/− cells. These results suggest that ASDcauses cytokine production predominantly in a TLR4/MyD88-dependent pathway. When WT and TLRs 2 −/− , 4 −/− , and MyD88 −/− BALB/c mice were intratracheally challenged with OVA and/or ASD, ASDcaused exacerbationof lung eosinophiliaalong with Th2 cytokine and eosinophil-relevant chemokine production. Serum OVA-specific IgE and IgG1 similar to WT was observed in TLRs 2 −/− , 4 −/− mice, but not in MyD88 −/− mice. The Th2 responses in TLR2−/− mice were attenuated remarkably by PMB. These results indicate that ASD exacerbateslung eosinophiliain a MyD88-dependent pathway. TLRs 2 and 4 signaling may be important in the increase in lung eosinophilia. Also, the TLR4ligand LPS and TLR2ligand like β-glucan may be strong candidates for exacerbationof lung eosinophilia.