Serum IgG N-glycans act as novel serum biomarkers of ankylosing spondylitis

Ankylosing spondylitis (AS) is a chronic inflammatory disease with poorly defined aetiologies and no curative treatments. The average delay in the diagnosis of AS is 6–8 years.1 Human leukocyte antigen B27 (HLA-B27) is a key laboratory marker for AS presenting in at least 90% of patients with AS.2 However, 63%–90% of patients with reactive arthritis3 and 19.2% of patients with psoriatic arthritis (PsA)4 are also positive for HLA-B27, indicating low specificity of HLA-B27. The risk of development of AS in an HLA-B27-positive individual is only 2%–10%,5 which suggests the limited value of HLA-B27 in supporting an AS diagnosis. Moreover, reported serum biomarkers for AS have generally exhibited low sensitivity or specificity6 (<60%). Novel serum biomarkers with high prediction capacity remain needed. The changed IgG glycosylation in autoimmune and inflammatory conditions, as well as the broad roles for specific IgG glycoforms in maintaining immune homeostasis, have been well documented.7 8 However, specific glycan biomarkers on IgG for AS have not been fully identified. In our previous study, a specialised microfluidic titanium dioxide-porous graphitised carbon chip was developed; this approach enabled the quantification of low-abundance and trace acidic glycans that are often biologically …