6644 Glycosylation Patterns of the IgG Variable Region in Thyroglobulin Antibodies and Their Impact on Antigen Binding Affinity

Abstract

Disclosure: S. Wang: None. Y. Cao: None. C. Zhao: None. C. Huang: None. K. Zhao: None. Y. Li: None. Y. Huang: None. Z. Ying: None. Y. Zhang: None. Y. Gao: None.

Objective: Thyroglobulin antibodies (TgAb), key serological markers in Hashimoto's thyroiditis (HT) patients, are predominantly in immunoglobulin G (IgG) form. Prior research has highlighted the importance of increased glycosylation in TgAb IgG from HT patients. This study investigates the unique glycosylation patterns of F(ab')₂ fragments in TgAb IgG in HT patients, compared to healthy individuals. It focuses on how these patterns differ and their impact on binding to thyroglobulin (Tg). Exploring the role of N-glycosylation in the F(ab')₂ segment of TgAb IgG is crucial for understanding its effect on immune responses in HT, potentially unveiling key mechanisms of the disease. Methods: To assess serum TgAb levels in HT patients (n≥28), we used an electrochemiluminescence immunoassay, dividing patients into medium-level (mHT, n≥14) and high-level (hHT, n≥14) groups. TgAb IgG was isolated from serum of both HT and control groups (n = 14) using affinity chromatography. TgAb IgG was then cleaved with Ides enzyme to yield TgAb IgG F(ab’)2 and Fc fragments. The F(ab')2 fragment of TgAb IgG underwent MALDI-QIT-TOF-MS mass spectrometry for glycosylation profiling. Additionally, mixed TgAb IgG was separated using columns that recognize mannose and terminal sialic acid, yielding high mannose and high terminal sialic acid TgAb IgG. Different TgAb IgG glycoforms were prepared through enzymatic treatment with peptide-N-glycosidase F, β1-4 galactosidase, and α2-3,6,8 neuraminidase. The binding affinity of these TgAb IgG to Tg antigen was measured using Tg specific ELISA and surface plasmon resonance (SPR). Results: Using MALDI-TOF MS, we identified 22 IgG glycan types in both HT and control (Con) groups. In the hHT group, six glycan types (G0F, G1F, G2F, M5A1, A3G1F, A3F) were upregulated compared to Con, with statistical significance (p < 0.05). The mHT group showed increased levels of G1F and G2F compared to Con (p < 0.05). Between hHT and mHT, only A3F was significantly elevated (p < 0.05). Removal of N-glycosylation from IgG TgAb F(ab)2 reduced binding to Tg antigen. Presence of both mannose and terminal sialic acid in TgAb enhanced the binding to Tg. Conclusions: Most TgAb IgG in the variable region of HT patients contain N-glycans. The glycosylation patterns of TgAb IgG F(ab)2 in HT differ significantly from healthy controls, affecting antibody binding affinity. Our findings reveal the complex role of glycosylation patterns in TgAb IgG, providing new insights into HT pathogenesis and potential research directions.

Presentation: 6/1/2024