Endoglycosidase treatment abrogates IgG arthritogenicity: Importance of IgG glycosylation in arthritis

Abstract

The glycosylation status of IgG has been implicated in the pathology of rheumatoid arthritis. Earlier, we reported the identification of a novel secreted endo-b-Nacetylglucosaminidase (EndoS), secreted by Streptococcus pyogenes that specifically hydrolyzes the b-1,4-di-N-acetylchitobiose core of the asparagine-linked glycan of human IgG. Here, we analyzed the arthritogenicity of EndoS-treated collagen type II (CII)-specific mouse mAb in vivo. Endoglycosidase treatment of the antibodies inhibited the induction of arthritis in (BALB/c  B10.Q) F1 mice and induced a milder arthritis in B10.RIII mice as compared with the severe arthritis induced by non-treated antibodies. Furthermore, EndoS treatment did not affect the binding of IgG to CII and their ability to activate complement, but it resulted in reduced IgG binding to FccR and disturbed the formation of stable immune complexes. Hence, the asparagine-linked glycan on IgG plays a crucial role in the development of arthritis. IntroductionThe impact of glycosylation, one of the most important post-translational modifications, on the structure and biological properties of glycoproteins has been well documented [1,2]. IgG molecules are mainly glycosylated at Asn-297 of the CH2 domain within the Fc region [3,4], with variable galactosylation but limited sialylation. The remaining glycosylation occurs in the hypervariable regions of the Fab region, with the position and frequency of occurrence being dependent on the presence of the consensus sequence Asn-Xaa-Thr/ Ser for N-glycosylation, and is characterized by a high incidence of sialylated structures. Murine IgG contain 2.3 asparagine-linked (N-linked) biantennary oligosaccharide chains per molecule [5], and human IgG contain 2.8 [6]. The minimal oligosaccharide structure is a hexasaccharide (GlcNAc2Man3GlcNAc) with variable sugar residues attached, which results in the generation of the multiple glycoforms. About 30 variants of biantennary chains occur, resulting in Clinical immunology

In vivo enzymatic modulation of IgG glycosylation inhibits autoimmune disease in an IgG subclass-dependent manner

“…In contrast to PNGaseF, this enzyme does not remove the entire sugar moiety but keeps one N-acetylglucosamine (GlcNAc) of the core sugar structure and its branching fucose residue that is present in the majority of the serum IgG pool. In our previous studies, we were able to show that treatment of mouse and human IgG subclasses with EndoS in vitro results in a severely reduced affinity to cellular Fc␥Rs (7,10). Injection of EndoS-treated autoantibody preparations generated in rabbits resulted in a dramatic reduction of antibody activity in vivo, further supporting the notion that cellular Fc␥Rs are the crucial mediators of antibody activity (9).…”

“…1A). We and others have shown that EndoS efficiently hydrolyzes the IgG-associated sugar moiety in human and rabbit serum and on purified antibodies (7,9,10). Because the focus of this work was to investigate the effect of EndoS application in mouse in vivo models of induced and established autoimmune disease, we first set out to identify the conditions for optimal IgG glycan hydrolysis.…”

“…Interestingly, however, some of the mouse and human IgG subclasses, such as mouse IgG2a and human IgG2, still showed significant affinities for activating Fc␥Rs (7,10). This important point remained open in our earlier studies because we used an arthritis model system in which the induction of autoimmune disease was crucially dependent on coinjection of active IgG2a and IgG2b subclasses specific for type II collagen (16).…”

“…Recently, an endoglycosidase (EndoS) isolated from Streptococcus pyogenes was shown to cleave specifically the sugar moiety of IgG and not of IgM Ig isotypes, thus representing an interesting molecular tool to modulate IgG glycosylation in vivo (7)(8)(9)(10). In contrast to PNGaseF, this enzyme does not remove the entire sugar moiety but keeps one N-acetylglucosamine (GlcNAc) of the core sugar structure and its branching fucose residue that is present in the majority of the serum IgG pool.…”

IgG glycan hydrolysis by a bacterial enzyme as a therapy against autoimmune conditions

“…This hypothesis was further stimulated by our recent finding that pretreatment of arthritogenic autoantibodies with EndoS abrogates the development of disease in a mouse model of collagen-induced arthritis (23). The IgG-specific protease IdeS also has been shown to be efficient in a similar model system (24) and in the mouse model of ITP used in this study (25).…”