Ykl-40 and phenotyping of severe asthma

Background: The aim of this study was to evaluate the role of serum and sputum YKL-40 measurements as biomarkers in severe asthma phenotypes. Material and Methods: 243 adult subjects (48.9±14.2 years) from the Wessex Severe Asthma Cohort (WSAC), spirometry according to BTS/SIGN guidelines; sputum induction with inhaled hypertonic saline in 99 subjects. Serum and sputum levels of YKL-40 were determined by ELISA (Quidel corporation, San Diego, California, USA). Statistical analysis used SPSS (version 22) ; statistical significance at p Results: We observed correlation between markers of airway neutrophilia and sputum YKL-40 levels. Sputum YKL-40 was strongly correlated with both sputum MPO (Spearman’s rho 0.733; p≤0.001) and sputum absolute neutrophil count (Spearman’s rho 0.663; p≤0.001), but not serum levels of YKL-40. Sputum (p=0,025), but not serum(p=0,753), YKL-40 levels were also significantly different across the inflammatory cell subtypes in sputum. When comparing YKL-40 levels in serum and sputum between SARP clusters, serum ( p=0.002), but not sputum (p=0.081) YKL-40 levels were significantly different between phenotypes (namely differentiating clusters 1 and 2 from 3, 4 and 5). Conclusions: It is thus apparent that serum YKL-40 and sputum YKL-40 are reflecting different processes within the airways. Serum YKL-40 might reflect a more systemic inflammation opposed to sputum YKL-40 that might reflect more local: airway inflammation.