{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\n Chitotriosidase (CHIT1) is an active chitin‐degrading enzyme produced primarily by activated macrophages that serves dual roles as an effector molecule in innate immunity and as a sensitive biomarker in a wide range of inflammatory and degenerative conditions. Elevated CHIT1 activity reflects macrophage activation in vascular disorders such as atherosclerosis, where increased serum levels correlate with the extent of atherosclerotic lesions."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "1"}]}, {"type": "t", "text": " In lysosomal storage diseases – including Gaucher and Niemann–Pick type B – accumulation of lipid‐laden macrophages is accompanied by significantly increased CHIT1 activity, which has proven useful for disease diagnosis and monitoring."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "2", "end_ref": "4"}]}, {"type": "t", "text": " In chronic airway diseases such as asthma and chronic obstructive pulmonary disease, lung chitinase activity in bronchoalveolar lavage fluid predominantly reflects CHIT1 expression, with activity levels that are relatively insensitive to corticosteroid treatment and are further modulated by environmental exposures like cigarette smoke."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "5"}]}, {"type": "t", "text": ""}]}, {"type": "t", "text": "\n \n "}, {"type": "p", "children": [{"type": "t", "text": "\n In the central nervous system, increased CHIT1 levels in cerebrospinal fluid and postmortem tissue have been associated with microglial and macrophage activation in neurodegenerative disorders such as amyotrophic lateral sclerosis and frontotemporal dementia, where CHIT1 concentrations correlate with disease progression and severity."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "7", "end_ref": "9"}]}, {"type": "t", "text": " Moreover, CHIT1 mediates the enzymatic processing of chitin substrates to produce small, diffusible oligomers that may in turn modulate immune responses during infection and inflammation."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "10"}]}, {"type": "t", "text": "\n "}]}, {"type": "t", "text": "\n \n "}, {"type": "p", "children": [{"type": "t", "text": "\n Additional studies have demonstrated that CHIT1 expression increases markedly during the differentiation of monocytes into macrophages and is linked to both innate and adaptive immune responses."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "11"}]}, {"type": "t", "text": " In systemic sclerosis–associated interstitial lung disease, CHIT1 amplifies pro‐fibrotic signaling by interacting with transforming growth factor–β1 to enhance receptor expression and downstream signaling, thereby contributing to tissue remodeling."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "12"}]}, {"type": "t", "text": " Furthermore, in sarcoidosis, serial measurement of serum CHIT1 accurately reflects the burden of granulomatous inflammation and correlates with both radiographic stage and therapeutic response."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "4"}]}, {"type": "t", "text": "\n "}]}, {"type": "t", "text": "\n \n "}, {"type": "p", "children": [{"type": "t", "text": "\n Genetic variation in the CHIT1 gene—including a common 24‐bp duplication that yields a null allele along with other missense mutations—significantly affects enzyme activity and has implications for both disease susceptibility and the interpretation of CHIT1 as a clinical biomarker. Population studies have documented variation in CHIT1 activity among different ethnic groups, and these polymorphisms may modulate the host’s response to infections such as Gram‐negative bacteria or contribute to atopic phenotypes."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "13", "end_ref": "15"}]}, {"type": "t", "text": "\n "}]}, {"type": "t", "text": "\n \n "}, {"type": "p", "children": [{"type": "t", "text": "\n Collectively, findings from multiple studies underscore the multifaceted role of CHIT1 in linking chitin degradation to immune regulation, tissue remodeling, and inflammation. Its robust association with macrophage activation not only supports its proposed role in host defense against chitin‐containing pathogens but also establishes CHIT1 as a promising biomarker for monitoring disease activity and therapeutic response in systemic inflammatory, neurodegenerative, and lysosomal storage disorders."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "16", "end_ref": "19"}]}, {"type": "t", "text": "\n "}]}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "Marta Artieda, Ana Cenarro, Alberto Gañán, et al. 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