Inhibitory Fc-Gamma IIb Receptor Signaling Induced by Multivalent IgG-Fc Is Dependent on Sialylation

Abstract

Immunoglobulin (IgG) Fc glycosylation has been shown to be important for the biological activity of antibodies. Fc sialylation is important for the anti-inflammatory activity of IgGs. However, evaluating the structure–activity relationship (SAR) of antibody Fc glycosylation has been hindered using simplified in vitro models in which antibodies are often displayed in monomeric forms. Presenting antibodies in monomeric forms may not accurately replicate the natural environment of the antibodies when binding their antigen in vivo. To address these limitations, we used different Fc-containing molecules, displaying their Fc domains in monovalent and multivalent fashion. Given the inhibitory role of Fc gamma receptor IIb (FcγRIIb) in autoimmune and inflammatory diseases, we focused on evaluating the impact of Fc sialylation on the activation of FcγRIIb. We report for the first time that in human cellular systems, sialic acid mediates the induction of FcγRIIb phosphorylation by IgG-Fc when the IgG-Fc is displayed in a multivalent fashion. This effect was observed with different types of therapeutic agents such as sialylated anti-TNFα antibodies, sialylated IVIg and sialylated recombinant multivalent Fc products. These studies represent the first report of the specific effects of Fc sialylation on FcγRIIb signaling on human immune cells and may help in the characterization of the anti-inflammatory activity of Fc-containing therapeutic candidates.

Site-Specific Glycosylation Analysis of Human and Murine Fcγ Receptor II Family Members Reveals Variant-Specific N-Glycosylation

“…Two FcγRIIA isoforms, FcγRIIA1 and FcγRIIA2, also produced by alternate splicing, differ in that the latter consists only of the soluble extracellular domain of the receptor. , FcγRII gene family members have been implicated in multiple immune and hematologic disorders. − Single nucleotide polymorphisms in FcγRII genes impact receptor function, localization to lipid rafts, expression, and ligand (IgG) binding affinity. ,, An FcγRIIA R134H substitution (also referred to as R131H) has been shown to enhance the binding of IgG2 and IgG3 . Moreover, a correlation between the expression of the FcγRIIA-H134 variant and the development of systemic lupus erythematosus (SLE) has been reported, though the precise mechanism of this difference is unclear. , Other studies have shown the opposite or no correlation, ,, suggesting that this effect may be population-dependent and/or arise via interaction with other genes.…”