Differential glycosylation of polyclonal IgG, IgG-Fc and IgG-Fab isolated from the sera of patients with ANCA-associated systemic vasculitis

• Published in: Biochimica et biophysica acta Vol. 1760; no. 4; pp. 669 - 677
• Main Authors: Holland, M., Yagi, H., Takahashi, N., Kato, K., Savage, C.O.S., Goodall, D.M., Jefferis, R.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.04.2006
• Subjects: Antibodies, Antineutrophil Cytoplasmic - blood; Case-Control Studies; Galactose; Glycosylation; Humans; IgG, ANCA; IgG-Fc/IgG-Fab glycosylation; Immunoglobulin Fab Fragments - blood; Immunoglobulin Fab Fragments - chemistry; Immunoglobulin Fc Fragments - blood; Immunoglobulin Fc Fragments - chemistry; Immunoglobulin G - blood; Immunoglobulin G - chemistry; Oligosaccharides - analysis; Post-translational modifications; Protein Processing, Post-Translational; Vasculitis - immunology; IgG-Fc/IgG-Fab glycosylation; IgG, ANCA; Post-translational modifications
• ISSN: 0304-4165; 0006-3002; 1872-8006
• DOI: 10.1016/j.bbagen.2005.11.021

Post-translational modifications (PTMs) of proteins produced in vivo may be tissue, developmentally and/or disease specific. PTMs impact on the stability and function of proteins and offer a challenge to the commercial production of protein biotherapeutics. We have previously reported a marked deficit in galactosylation of oligosaccharides released from polyclonal IgG isolated from sera of patients with the anti-neutrophil cytoplasmic antibodies (ANCA) associated vasculitides; Wegener's granulomatosis (WG) and microscopic polyangiitis (MPA). Whilst normal polyclonal IgG molecules are glycosylated within the IgG-Fc region, ∼20% of molecules also bear oligosaccharides attached to the variable regions of the light or heavy chain IgG-Fab. It is of interest, therefore to compare profiles of oligosaccharides released from the IgG-Fc and IgG-Fab of normal IgG with that isolated from the sera of patients with WG or MPA. This study shows that whilst the oligosaccharides released from ANCA IgG-Fc are hypogalactosylated those released from IgG-Fab are galactosylated and sialylated. These results show that hypogalactosylation of IgG-Fc is not due to a defect in the glycosylation or processing machinery. It rather suggests a subtle change in IgG-Fc conformation that influences the addition of galactose. Remarkably, this influence is exerted on all plasma cells. Interestingly, a licensed monoclonal antibody therapeutic, produced in Sp2/0 cells, is also shown to be hypogalactosylated in its IgG-Fc but fully galactosylated in its IgG-Fab.