SFTPD and chronic obstructive pulmonary disease: A reduction in BAL SP‐D and concomitant increase in sSP‐D has also been observed in patients with COPD and in subjects exposed to tobacco smoke37, 38 and has been proposed to reflect nonspecific inflammation within the distal airways and alveoli, suggesting an impaired endothelial barrier and altered permeability which allows leakage of both full‐size and degraded SP‐D into serum.5