The complex allergen house dust mite (HDM) acts directly on macrophages to stimulate actin remodeling

Abstract

Asthma is a chronic inflammatory disease of the lungs that results in narrowing of the airways, making it difficult to breathe. Dust is a common trigger of allergy and asthma. House dust mites (HDM) are the main cause of dust allergies. Despite the fact that macrophages are present in abundant amounts within the lung and are one of the first cells exposed to HDM upon inhalation, little is known about the direct effects of HDM on macrophages. Here we demonstrate that HDM can directly act on bone marrow-derived macrophages (BMM) leading to actin remodeling. BMM treated with HDM demonstrated alterations in F-actin (based on Phalloidan staining), changes in shape, and increases in size significantly. We also observed alterations in the phosphorylation of cofilin and slingshot, two proteins that regulate actin polymerization. BMM demonstrated constitutive phosphorylation of cofilin with little phosphorylated slingshot at baseline. However, HDM treatment diminished cofilin phosphorylation while increasing the phosphorylation of slingshot. Since HDM is known to contain LPS, important for HDM-induced allergic inflammation in vivo, we examined the contribution of LPS to actin remodeling. Actin cytoskeleton changes were still evident in BMM treated with HDM in the presence of polymyxin B (PMB) or in Tlr4^−/− BMM, although the average cell size was reduced compared to HDM alone. The HDM-induced changes in phosphorylation of cofilin and slingshot were unaffected by PMB or Tlr4 deficiency. These results suggest that HDM induces actin remodeling in macrophages by a mechanism that is largely LPS/TLR4-independent. These observations provide an opportunity to identify novel therapeutic targets for allergic asthma.