Journal
GLYCOBIOLOGY
Volume 32, Issue 9, Pages 803-813Publisher
OXFORD UNIV PRESS INC
DOI: 10.1093/glycob/cwac039
Keywords
ST6Gal1; IgG; sialic acid; plasma; hepatocyte
Categories
Funding
- National Institute for General Medical Sciences [GM115234]
- National Institute for Allergy and Infectious Disease [AI089474, AI154899]
- National Institute of General Medical Sciences [GM103694, GM137763]
- National Institutes of Health Shared Resource Grant [OD021559]
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The glycosylation of IgG is important for its function, but the mechanisms and factors involved are not well understood. This study suggests that alpha 2,6-sialylation of IgG occurs after release from B cells and is not dependent on plasma-localized ST6Gal1 activity.
The glycosylation of immunoglobulin G (IgG) has attracted increased attention due to the impact of N-glycan modifications at N297 on IgG function, acting primarily through modulation of Fc domain conformation and Fc gamma receptor-binding affinities and signaling. However, the mechanisms regulating IgG glycosylation and especially alpha 2,6-sialylation of its N-glycan remain poorly understood. We observed previously that IgG is normally sialylated in mice with B cells lacking the sialyltransferase ST6Gal1. This supported the hypothesis that IgG may be sialylated outside of B cells, perhaps through the action of hepatocyte-released plasma ST6Gal1. Here, we demonstrate that this model is incorrect. Animals lacking hepatocyte expressed ST6Gal1 retain normal IgG alpha 2,6-sialylation despite the lack of detectable ST6Gal1 in plasma. Moreover, we confirmed that B cells were not a redundant source of IgG sialylation. Thus, while alpha 2,6-sialylation is lacking in IgG from mice with germline ablation of ST6Gal1, IgG alpha 2,6-sialylation is normal in mice lacking ST6Gal1 in either hepatocytes or B cells. These results indicate that IgG alpha 2,6-sialylation arises after release from a B cell but is not dependent on plasma-localized ST6Gal1 activity.
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