The Immune Microenvironment of Hashimoto’s Thyroiditis Regulates the Glycosylation Modification of IgG

Objectives: Elevation of anti-thyroglobulin antibodies that are primarily IgG isotype is a hallmark of Hashimoto’s thyroiditis (HT). As for IgG,it bears two conserved repertoire of N-linked glycans attached to its crystallizable fragment (Fc) at the 297 asparagine residue (Asn297). In our previous study, we found that serum TgAb IgG from HT patients exhibits higher glycosylation levels than those observed from healthy controls. Previous studies confirmed that imbalance of Th1/Th2 and Th17/Treg leading to altered immune microenvironment with elevation of certain cytokines was found in the thyroid tissue of HT, including IFN-γ, TNF-α, IL-21, IL-17A, IL-6, BAFF, APRIL. Thus, the aim of our study was to investigate the influence of the elevated cytokines on the differentiation process of B cells and the glycosylation levels of IgG. Methods: We formed a two-phase culture system in vitro to promote B cells to differentiate to antibody-secreting cells (ASCs). In the process of cell culture, B cells were co-cultured with cytokines as followed: IFN-γ, TNF-α, IL-21, IL-17A, IL-6, BAFF and APRIL. Flow cytometry was performed to identify the percentage of plasmablasts (CD38(+)CD27(high)) and plasma cells (CD20(-)CD138(+)). ELISA was used to measure the yield of IgG in culture supernatants. The glycosylation levels of secreted IgG under different stimulation conditions were detected by lectin microarray. Results: We found that IL-21, TNF-α and BAFF can significantly promote the differentiation of B cells into ASCs in vitro culture system, and augment the production of IgG to over 4-fold. In addition, cytokines affected the glycosylation modification profile of IgG diversely: 1) IL-21, IL-17A, TNF-α, BAFF significantly increased the glycosylation level of sialic acid of total IgG; 2) IFN-γ significantly increased the level of galactose; 3) IL-21, IL-17A, IFN-γ, BAFF, and APRIL significantly increased the level of mannose; 4) IL-6 significantly decreased the level of sialic acid, galactose and mannose; 5) IL-17A, IFN-γ, TNF-α, BAFF significantly increased the level of GalNAc that was a component of O-Glycan,which only exists in the hinge region of IgG3 subclass. Conclusions: The abnormally elevated cytokines in microenvironment participated in the regulation of B cell terminal differentiation process and glycosylation level of IgG, thereby involving in the pathogenesis of AITD.