The biomarkers analysed in the present study potentially have biological plausibility in that IL-1β and IL-8 are pro-inflammatory cytokines, while MMP-8, MMP-9 and HNE may be released from activated neutrophils during degranulation, and one might expect these mediators to be elevated in regions of lung in which there is active infection. This evidence concerns the gene CXCL8 and infection.