CCL1 and chronic obstructive pulmonary disease: Prior to this study, we demonstrated that single-nucleotide polymorphisms (SNPs) in the CCL1 gene are associated with chronic obstructive pulmonary disease (COPD) exacerbation (Takabatake et al. 2006), that is mainly caused by respiratory tract infection and induces acute worsening of symptoms from the usual stable state (Hurst et al. 2006; Patel et al. 2002; Wilkinson et al. 2006).