Thesis Gillian Dekkers
On 1 December 2017 Gillian Dekkers defended her PhD thesis 'Influence of immunoglobulin G-glycan and subclass variation on antibody effector functions' at the University of Amsterdam.
Promotor: Prof CE van der Schoot MD PhD
Copromotores: T Rispens PhD and G Vidarsson PhD
Venue: Agnietenkapel, University of Amsterdam
Summary
Antibodies signal to other parts of the immune system by binding of their constant domain (Fc) to receptors, such as Fc gamma receptors (FcγR) or C1q of the complement system in the case of immunoglobulin G (IgG). For these interactions the Fc-structure, influenced by subclasses or glycan-composition of the constant domain, is important. The research in this thesis aimed to further understand the effect IgG constant domain variation on the different effector functions.
A glyco-engineering toolset was developed to change every glycan end groups (galactose, sialic acid, fucose, bisection) of the IgG-Fc glycan. Using this, we show that C1q binding and classical complement activation were increased by addition of galactose and sialic acid.
Absence of fucose increases affinity of IgG for FcγRIII and was additionally enhanced by galactose addition. The composition of different FcγRs on effector cells is important for the effector function of IgG glycoforms. It was shown macrophages bearing all kinds of FcγR are unaffected, whilst NK cells bearing solely FcγRIIIa, are affected by changes in IgG-Fc glycan composition.
Affinity of all human IgG subclasses for the mouse FcγRs was determined and show that each subclass has a specific binding pattern. Mouse glycoforms are similarly affected by lack of fucose for binding to the mouse orthologue FcγRIII, where a single glycan in these orthologous receptors discriminates for fucosylated and afucosylated IgG.
Lastly we show presence of O-glycans in the hinge of IgG3 of which the function is yet unknown.
Chapters
Chapter 1
General introduction and scope of the thesis
Chapter 2
Multi-level glyco-engineering techniques to generate IgG with defined Fc-glycans. abstract
Chapter 3
Decoding the human IgG-glycan repertoire reveals a spectrum of Fc-receptor- and complementmediated-effector activities
Chapter 4
Inhibition of FcγR-mediated phagocytosis by IVIg is independent of IgG-Fc sialylation and FcγRIIb in human macrophages. abstract
Chapter 5
Enhanced effector functions due to antibody defucosylation depend on the effector cell Fcγ receptor profile. abstract
Chapter 6
Affinity of human IgG subclasses to mouse Fc gamma receptors. abstract
Chapter 7
Conserved FcγR- glycan discriminates between fucosylated and afucosylated IgG in humans and mice
Chapter 8
Hinge-region O-glycosylation of human immunoglobulin G3 (IgG3). abstract
Chapter 9
General discussion
Appendix