IgG glycosylation in autoimmune diseases

Abstract

Immunoglobulin G (IgG) is the most abundant glycoprotein in human serum. All IgG subclasses have a single-conserved N-linked glycosylation site at Asn297 of the heavy chain and 10–30% of IgGs are N-glycosylated also in a Fab region. N-glycans of Fc are sialylated and fucosylated biantennary complex-type structures. Glycosylation plays a key role in antibody function, and IgG N-glycans are essential for the proper activity of the immune system. Fc glycans are important for IgG effector functions, whereas Fab oligosaccharides modulate antigen binding. Glycosylation changes of IgG are associated with the development of various human diseases, including autoimmune states. The modification of one sugar moiety in N-glycan structure may result in the stimulation or suppression of immune response. The lack of core fucose leads to the enhancement of pro-inflammatory activity, whereas an increase of sialylation determines immunosuppressive properties of IgG. The contribution of IgG Fc glycosylation changes has been demonstrated in the pathogenesis of rheumatoid arthritis, lupus erythematosus and Crohn’s disease. A decrease in IgG galactosylation and sialylation, found in these diseases, activates effector cells and triggers inflammatory reactions. A detailed analysis of changes in IgG glycosylation and their effects on the development of autoimmune diseases is important in the treatment of these diseases. IgGs with modified α2,6-sialylation are used as therapeutic antibodies with anti-inflammatory properties. Numerous studies on IgG glycosylation have provided evidence of the role of this post-translational modification in the proper functioning of antibodies and the importance of changes in the structure of IgG glycans, mainly incomplete galactosylation and desialylation, in the pathogenesis of many diseases. The continuation of these studies may contribute to explaining the mechanisms of autoimmunity that is still poorly understood.