AUTHOR=Specjalski Krzysztof , Romantowski Jan , Niedoszytko Marek 

TITLE=YKL-40 as a possible marker of neutrophilic asthma

JOURNAL=Frontiers in Medicine

VOLUME=Volume 10 - 2023

YEAR=2023

URL=https://www.frontiersin.org/journals/medicine/articles/10.3389/fmed.2023.1115938

DOI=10.3389/fmed.2023.1115938

ISSN=2296-858X

ABSTRACT=    Asthma is a heterogenous disease with patients varied in terms of inflammation pattern, concomitant pathologies and factor aggravating its course. As a result there is a need for sensitive and specific biomarkers that could facilitate diagnosing asthma as well as phenotyping and endotyping.
   Chitinases are evolutionarily conserved hydrolases degrading chitin. In contrast, CLPs bind chitin but do not have degrading activity. Chitinases and CLPs are produced by neutrophils, monocytes and macrophages in response to parasitic or fungal infection. 
   Several studies demonstrated that overexpression of CLP YKL-40 was associated with asthma. Moreover, it correlated with exacerbation rate, therapy-resistance, poor control of symptoms and inversely – with FEV1. YKL-40 facilitated allergen sensitization and IgE production in animal models. Its concentration was elevated in bronchoalveolar lavage fluid after allergen challenge. It was also found to promote proliferation of bronchial smooth muscle cells and correlate with subepithelial membrane thickness. Thus, it may be involved in bronchial remodeling. 
    Associations between YKL-40 and particular asthma phenotypes remain unclear. Some earlier studies showed that YKL-40 correlated with blood eosinophilia and FeNO suggesting involvement in T2 high inflammation. Quite the opposite, cluster analyses revealed strong association with  severe neutrophilic and obesity-associated asthma. 
   The major drawback in practical application of YKL-40 is its low specificity. High serum levels of YKL-40 were found in COPD, several malignancies, infectious and autoimmune diseases. As a consequence it cannot be applied in differential diagnosis. However it  could be useful in phenotyping, especially together with other biomarkers.