IgG Fc sialylation is regulated during the germinal center reaction following immunization with different adjuvants

Background: Effector functions of IgG Abs are regulated by their Fc N-glycosylation pattern. IgG Fc glycans that lack galactose and terminal sialic acid residues correlate with the severity of inflammatory (auto)immune disorders and have also been linked to protection against viral infection and discussed in the context of vaccine-induced protection. In contrast, sialylated IgG Abs have shown immunosuppressive effects. Objective: We sought to investigate IgG glycosylation programming during the germinal center (GC) reaction following immunization of mice with a foreign protein antigen and different adjuvants. Methods: Mice were analyzed for GC T-cell, B-cell, and plasma cell responses, as well as for antigen-specific serum IgG subclass titers and Fc glycosylation patterns. Results: Different adjuvants induce distinct IgG⁺ GC B-cell responses with specific transcriptomes and expression levels of the α2,6-sialyltransferase responsible for IgG sialylation that correspond to distinct serum IgG Fc glycosylation patterns. Low IgG Fc sialylation programming in GC B cells was overall highly dependent on the Foxp3^– follicular helper T (T_FH) cell–inducing cytokine IL-6, here in particular induced by water-in-oil adjuvants and Mycobacterium tuberculosis. Furthermore, low IgG Fc sialylation programming was dependent on adjuvants that induced IL-27 receptor–dependent IFN-γ⁺ T_FH1 cells, IL-6/IL-23–dependent IL-17A⁺ T_FH17 cells, and high ratios of T_FH cells to Foxp3⁺ follicular regulatory T cells. Here, the 2 latter were dependent on M tuberculosis and its cord factor. Conclusion: This study's findings regarding adjuvant-dependent GC responses and IgG glycosylation programming may aid in the development of novel vaccination strategies to induce IgG Abs with both high affinity and defined Fc glycosylation patterns in the GC.