Fc N-glycosylation heterogeneity of anti-MDA5 IgG is associated with interstitial lung disease severity via regulating FcγR/C1q signaling in MDA5 + dermatomyositis: a cross‑sectional study

Abstract Background To characterize Fc N-glycosylation patterns of disease-specific IgG (DSIgG) in anti-MDA5-positive dermatomyositis (MDA5 + DM) and evaluate their associations with interstitial lung disease (ILD) severity. Methods Eighty-four patients with MDA5 + DM and 60 healthy controls were enrolled. Disease-specific anti-MDA5 IgG glycopeptides were analyzed by UPLC-MS/MS. Associations between glycoform features and ILD severity were assessed using correlation analysis, ROC analysis, and logistic regression. Surface plasmon resonance and in vitro functional assays were used to compare glycoform-dependent engagement of FcγRIIa, FcγRIIIa, and C1q, as well as downstream ADCP, ADCC, CDC, and endothelial inflammatory responses. Results Compared with controls, DSIgG1 from patients with MDA5 + DM showed higher fucosylation and lower sialylation. Severe ILD was associated with increased DSIgG1F and decreased DSIgG1S. In multivariable analysis, lower DSIgG1S remained independently associated with severe ILD (OR = 0.07, P = 0.0065), and DSIgG1S showed strong discriminatory performance for severe ILD (AUC = 0.9133). Functionally, G1S exhibited stronger FcγRIIa-related binding and phagocytic activity, whereas G1F displayed stronger FcγRIIIa and C1q binding, together with increased ADCC and CDC. In endothelial-cell experiments, the two glycoforms induced distinct inflammatory response patterns. Conclusion Anti-MDA5 DSIgG Fc glycosylation is associated with ILD severity in MDA5 + DM. Distinct glycoforms exhibit differential FcγR/C1q-related effector profiles, supporting a potential role for Fc glycosylation heterogeneity in disease stratification and pathogenesis.