Serum IgG Glycan Hallmarks of Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is a debilitating autoimmune disorder characterized by unknown pathogenesis and heterogeneous clinical manifestations. The current existing serum biomarkers for SLE have limited sensitivity or specificity, making early and precise diagnosis difficult. Here, we identified two N-glycans on serum immunoglobulin G (IgG) as excellent diagnostic biomarkers for SLE based on in-depth glycomic analyses of 389 SLE patients and 304 healthy controls. These two N-glycan biomarkers are specific for diagnosing SLE, as no significant changes in these biomarkers were observed in other systemic autoimmune diseases that are easily confused with SLE, such as rheumatoid arthritis, primary Sjögren's syndrome, or systemic sclerosis. Notably, the two N-glycan biomarkers proved to be autoantibody-independent and all-stage patient suitable. The two N-glycan biomarkers are demonstrated to be located on the Fc region based on fragment-specific glycan analysis and glycopeptide analysis, suggesting their close correlation with disease activity. Enzyme analyses revealed dysregulation of a series of glycotransferases in SLE, which might be responsible for the observed glycan alteration. Our findings provide insights into efficient population screening based on serum IgG glycosylation and potential new pathogenic factors of SLE.