Total brain-derived neurotrophic factor (BDNF) protein and its mature isoform in sputum. (A) Total BDNF protein (by ELISA) in sputum supernatants. (B) Representative Western blots of the three BDNF isoforms (precursor, truncated, and mature) in sputum supernatants from four healthy control subjects (HC), three subjects with mild asthma (Mild), four with mild–moderate asthma (Mild-Mod/inhaled corticosteroid [ICS]), and five with severe asthma (SA). (C) The ratio of the mature isoform to total BDNF measured by densitometry. (D) Total amount of mature BDNF (pg/ml). Data are presented as median, 25th, and 75th percentiles with maximum/minimum whiskers.