The IgG Fc domain mediates a range of antibody effector functions, including antibody dependent cell-mediated cytotoxicity (ADCC), complement activation, phagocytosis, and the recently emerged general anti-inflammatory effect of immunoglobulin therapy (IVIg). The conserved N-glycan attached to Fc N297 maintains the Fc structural integrity for the effector functions, while its glycoform is known to modulate the affinity for the Fc γ-receptors (FcγRs), complement, and the C-type lectin DC-SIGN. IgG Fc exhibits protein-directed glycosylation characterized by a series of biantennary complex type glycoforms, with a small population of sialylated species. The sialylated Fc has been proposed to bind DC-SIGN and initiate an anti-inflammatory signalling pathway. The restricted Fc glycan processing is partially attributed to the hydrophobic interaction between Fc glycan and the hydrophobic Fc protein backbone. Mutations within the hydrophobic Fc protein-glycan interface dramatically increases Fc glycan processing, while concomitantly decreases Fc affinity for the FcγRs. However, it is unclear whether this disrupted Fc-FcγR interaction was due to the increased terminal glycan processing, or the perturbed Fc protein-glycan interface. Here, the integrity of the Fc protein-glycan interface was demonstrated to be important in maintaining the productive Fc-FcγR interaction independently of glycoform. This glycoform-independent effect was exploited to generate novel inhibitory Fc variants. In addition, the interaction between sialylated IgG and the putative IVIg receptor DC-SIGN was re-evaluated. Analysis shows that IVIg binds DC-SIGN in a glycan-independent, Fab-mediated manner. Furthermore, the effect of IVIg sialylation on human antigen presenting cells was examined; evidence presented here indicate that IVIg deglycosylation, not desialylation, has an anti-inflammatory effect on human dendritic cells (DCs). These data suggest the need for a general re-evaluation of the current mechanistic model of anti-inflammatory IVIg.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:588455 |
| Date | January 2013 |
| Creators | Yu, Xiaojie |
| Contributors | Scanlan, Chris; Crispin, Max |
| Publisher | University of Oxford |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://ora.ox.ac.uk/objects/uuid:140048b3-7cf4-4a30-932b-59c3e1d20272 |
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