Serum YKL-40 Levels Measured In Antisynthetase Syndrome Patients

Antisynthetase syndrome (ASSD) is a rare systemic autoimmune myopathy characterized by muscle, joint, and pulmonary involvement, as well as by the presence of fever, “mechanic’s hands,” and Raynaud’s phenomenon.

The protein chitinase-3-like-1 (YKL-40) is a glycoprotein secreted by inflammatory cells, including macrophages and neutrophils. YKL-40 is associated with several physiological processes, such as inflammation, cell proliferation, angiogenesis, tissue fibrosis, and tissue remodeling.

Rheumatologists at the Universidade de Sao Paulo (Sao Paulo, Brazil) carried out a cross-sectional single-center study that took place from 2017 to 2019 and included 66 adult patients with ASSD followed up at the outpatient clinic. The patients’ mean age was 44.8 ± 11.8 years, and median disease duration was 1.5 (0.0–4.0) years. These patients were predominantly female (82.8%) and Caucasian (73.4%). Most patients had stable disease. Muscle involvement was defined as the presence of progressive and proximal limb muscle weakness, increased serum levels of muscle enzymes, such as creatine phosphokinase (CPK), myopathic pattern on electroneuromyography, and muscle biopsy compatible with inflammatory myopathy.

The scientists used a commercially available line blot test kit, the Myositis Profile Euroline Blot test kit, (Euroimmun, Lübeck, Germany; www.euroimmun.com) to identify anti-aminoacyl-tRNA synthetase autoantibodies (anti-Jo-1, anti-EJ, anti-OJ, anti-PL-7, anti-PL-12, and anti-Ro-52). The YKL-40 quantification was performed using a specific kit (Human CHI3L1 ELISA kit, RayBiotech, Peachtree Corners, GA, USA). The interferon gamma (IFN-γ) and TNF-α tests were performed using the LUMINEX 100/200x xMAP technology (Millipore, Burlington, MA, USA). Additionally, the YKL-40 expression and location were assessed in muscle tissues of three patients with ASSD, whose biopsies were taken from the vastus lateralis muscle upon diagnosis.

The investigators reported that the median YKL-40 serum level was significantly higher in patients with ASSD when compared to the healthy individuals: 538.4 (363.4–853.1) pg/mL versus 270.0 (201.8–451.9) pg/mL, respectively. However, YKL-40 serum levels did not correlate with any clinical, laboratory, disease status, or therapeutic parameters, except tumor necrosis factor alpha (TNF-α) serum levels. YKL-40 was highly expressed by inflammatory cells found in muscle biopsy specimens.

The authors concluded that there were high YKL-40 serum levels in patients with ASSD, and these correlated positively with TNF-α serum levels. Although other studies have shown the expression of YKL-40 in lungs of patients with various systemic autoimmune myopathies, they have shown high YKL-40 levels in inflammatory muscle tissue cells. The study was published on July 5, 2021 in the journal Advances in Rheumatology.

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Universidade de Sao Paulo 
Euroimmun
RayBiotech 
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