CCL18 and chronic obstructive pulmonary disease: To our knowledge, the current study is the first to show an association of serum CCL18 levels with increasing fibrocyte abundance in COPD, and has relevance in light of published data that emerged in the literature after the current study was undertaken, showing recruitment of blood fibrocytes during acute exacerbations of COPD, linked to worsening of clinically important endpoints including lung function and mortality [25].