CCL4 Functions as a Biomarker of Type 2 Airway Inflammation

Eosinophilic airway inflammatory disease is associated with bronchial asthma, with eosinophilic chronic rhinosinusitis (ECRS) typical of refractory type 2 airway inflammation. CCL4 produced at local inflammatory sites is involved in them via the accumulation and activation of type 2 inflammatory cells, including eosinophils. The detailed mechanism of CCL4 production remains unclear, and also the possibility it could function as a biomarker of type 2 airway inflammation remains unresolved. In this study, we evaluated CCL4 mRNA expression and production via the TSLP receptor (TSLPR) and toll-like receptors (TLRs) or proteinase-activated receptor-2 (PAR2) in BEAS-2B bronchial epithelial cells co-incubated with purified eosinophils or eosinophil peroxidase (EPX). We examined serum chemokine (CCL4, CCL11, CCL26, and CCL17) and total IgE serum levels, fractionated exhaled nitrogen oxide (FENO), and CCL4 expression in nasal polyps in patients with severe ECRS and asthma. CCL4 was induced by TSLP under eosinophilic inflammation. Furthermore, CCL4 was released via TLR3 signaling, which was enhanced by TSLP. CCL4 was mainly located in nasal polyp epithelial cells, while serum CCL4 levels were reduced after dupilumab treatment. Serum CCL4 levels were positively correlated with FENO, serum IgE, and CCL17 levels. Thus, CCL4 released from epithelial cells via the innate immune system during type 2 airway inflammation may function as a useful biomarker for the condition.