Although the increase in SP levels in mucus is equivocal in COPD [93], it has previously been reported that this neuropeptide may be involved in the pathogenesis of some of the changes observed in COPD, as evidenced by increased SP- and VIP-immunoreactivity reported in epithelium and glands from COPD patients [98]. This evidence concerns the gene VIP and chronic obstructive pulmonary disease.