B Cell Activation Pathways Dictate the Effector Profile of Secreted IgG through Differential Fc Glycosylation 2257228

Abstract

Abstract Introduction Glycosylation of IgG Fc is a critical modification, influencing IgG’s ability to bind to Fc receptors and complement, thereby defining its effector function. Despite this crucial role, mechanisms controlling the Fc glycosylation in B cells are poorly understood. Here, we sought to identify these mechanisms by mimicking T-cell-dependent and independent responses in vitro. Methods IgG+ memory B cells from healthy donors were stimulated to induce antibody-secreting cell differentiation. To define the upstream signals, IgG+ memory B cells were cultured via either T-cell-dependent (CD40L) or innate Toll-like receptor (TLR)-mediated pathways. IgG glycosylation was analyzed with Whole Immunoglobulin Glycoprofiling with Asymmetric Monitoring (WIgGWAM), a mass spectrometry method that analyzes glycan pairs on the intact Fc dimer. Results T-cell-dependent activation (CD40L) yielded IgG with significantly increased galactosylation and sialylation (glycans associated with anti-inflammatory activity) compared to TLR-mediated activation (R848 and CpG). Crucially, on asymmetrically glycosylated species, mono-sialylated Fc also differed significantly in its distribution between the T-cell-dependent and innate TLR activation conditions, revealing another layer of regulation. Conclusion B cell activation pathways represent a key checkpoint controlling IgG effector function. These findings suggest that T-cell-independent responses, which are prominent during active SLE and often driven by TLR engagement, may inherently generate more pro-inflammatory IgG characterized by reduced galactosylation and sialylation. Therapeutically manipulating specific B cell activation pathways represents a novel strategy to shape the IgG glycan profile towards a more anti-inflammatory state, offering a new approach to control antibody-mediated diseases. Funding Source This research was supported by the National Institute of Allergy and Infectious Diseases (NIAID) of the National Institutes of Health under award number U19 AI144306 Topic Categories Immune Response Regulation: Molecular Mechanisms (IRM)