Critical role of CCL4 in eosinophil recruitment into the airway

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Abstract

Background

Excessive eosinophil airway infiltration is a clinically critical condition in some cases. Eosinophilic pneumonia (EP) is a pulmonary condition involving eosinophil infiltration of the lungs. Although several chemokines, including eotaxin‐1 (CCL11), RANTES (CCL5) and macrophage inflammatory protein 1β (MIP‐1β or CCL4), have been detected in bronchoalveolar lavage fluid (BALF) from patients with EP, the pathophysiological mechanisms underlying EP, including potential relationships between eosinophils and CCL4, have not been fully elucidated.

Objective

To examine the involvement of CCL4 in eosinophilic airway inflammation.

Methods

We analysed supernatants of activated eosinophils and BALF from 16 patients with eosinophilic pneumonia (EP). Further, we examined the effects of CCL4 on eosinophil functions in vitro and those of anti‐CCL4 neutralising antibody in an in vivo model.

Results

We found that purified human eosinophils stimulated with IL‐5 predominantly secreted CCL4 and that patients with EP had elevated CCL11 and CCL4 levels in BALF compared with samples from individuals without EP. Because CCL4 levels was more strongly correlated with eosinophil count and expression of eosinophil granule proteins than CCL11, in vitro experiments using purified eosinophils concentrated on the former chemokine. Interestingly, CCL4 acted as a chemoattractant for eosinophils. In a mouse model, administration of a CCL4‐neutralising antibody attenuated eosinophilic airway infiltration and airway hyper‐responsiveness.

Conclusions & Clinical Relevance

Overall, these findings highlight an important role of CCL4 in the mechanisms underlying eosinophil recruitment into the airway and may provide a novel insight into this potential therapeutic target.

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