AB0020 ACPA ILLUSTRATING THE IMPACT OF IGG FAB-GLYCOSYLATION ON TRANSPLACENTAL TRANSFER OF ANTIBODIES AND THEIR BINDING TO THE NEONATAL FC-RECEPTOR (FCRN)

Abstract

Background:Fc neonatal receptor (FcRn) is crucial for IgG half-life and transplacental transport. Different sites of IgG carry glycans which may affect binding to FcRn. While the effect of Fc-glycans has been investigated, the impact of Fab-glycosylation (~14% IgG) on IgG-FcRn interaction remains unclear. Anti-citrullinated protein antibodies (ACPA) of rheumatoid arthritis patients exhibit remarkably high Fab-glycosylation (~90%). This makes ACPA an ideal model to investigate how Fab-glycosylation influences IgG-FcRn interaction.Objectives:To investigate the potential impact of IgG Fab-glycosylation on IgG transplacental transfer and interaction with FcRn.Methods:To investigate transplacental transport of ACPA and total IgG, serum of ACPA-positive RA patients (mothers) as well as of healthy mothers and their respective newborns was analyzed. IgG Fab- and Fc-glycosylation was investigated with liquid chromatography and mass-spectrometry. Furthemore, ACPA monoclonal IgG were produced and glycoengineered to acquire several variants of the same monoclonal antibody differing only in their glycosylation profile. These glycovariants were then used to investigate the impact of Fab-glycans on the affinity of IgG for FcRn. Surface plasmon resonance (SPR) and affinity chromatography were implemented.Results:When measured in mothers’ serum and cord blood samples, Fab-glycosylation of IgG antibodies was ~20% lower in newborns compared to their mothers, which was observed for ACPA IgG, non-ACPA IgG in RA patients and total IgG of healthy controls (Figure 1). This may indicate that transplacental transfer of Fab-glycosylated antibodies is impaired. SPR results suggested that presence of Fab-glycans slightly lowered the affinity of IgG for FcRn. However, presence of Fab-glycans did not have a significant effect on the results of FcRn affinity chromatography. Together, these results suggest that Fab-glycans may impair association of IgG with FcRn, while dissociation likely stays intact.Conclusion:Our results suggest that Fab-glycans inhibit IgG-FcRn binding which negatively affects the transplacental transfer of Fab-glycosylated IgG. The impact of Fab-glycosylation on IgG half-life requires further investigation.Figure 1.Disclosure of Interests:Mikhail Volkov: None declared, Karin van Schie: None declared, Albert Bondt: None declared, Theresa Kissel: None declared, Maximilian Brinkhaus Grant/research support from: argenx, Arthur Bentlage: None declared, Carolien Koeleman: None declared, Steven de Taeye Grant/research support from: Genmab, Radboud Dolhain: None declared, Manfred Wuhrer: None declared, Rene Toes: None declared, Gestur Vidarsson: None declared, Diane van der Woude: None declared