YKL-40 as a biomarker in various inflammatory diseases: A review

Highlights YKL-40 is a biomarker for inflammatory diseases’ diagnosis and prediction YKL-40 concentration increases with age and has variations in healthy population YKL-40 is convincing in pancreatic/liver disease, arthritis, bronchitis, and sepsis YKL-40 is debatable in cardiovascular/neurological/renal disease, diabetes, asthma Future larger studies and age-stratified reference intervals of YKL-40 are needed YKL-40 or Chitinase-3-Like Protein 1 (CHI3L1) is a highly conserved glycoprotein that binds heparin and chitin in a non-enzymatic manner. It is a member of the chitinase protein family 18, subfamily A, and unlike true chitinases, YKL-40 is a chitinase-like protein without enzymatic activity for chitin. Although its accurate function is yet unknown, the pattern of its expression in the normal and disease states suggests its possible engagement in apoptosis, inflammation and remodeling or degradation of the extracellular matrix. During an inflammatory response, YKL-40 is involved in a complicated interaction between host and bacteria, both promoting and attenuating immune response and potentially being served as an autoantigen in a vicious circle of autoimmunity. Based on its pathophysiology and mechanism of action, the aim of this review was to summarize research on the growing role of YKL-40 as a persuasive biomarker for inflammatory diseases’ early diagnosis, prediction and follow-up (e.g., cardiovascular, gastrointestinal, endocrinological, immunological, musculoskeletal, neurological, respiratory, urinary, infectious) with detailed structural and functional background of YKL-40