Sialylation Determines the Nephritogenicity of IgG3 Cryoglobulins

Abstract

Monoclonal 6-19 IgG3 anti-IgG2a rheumatoid factor derived from lupus-prone MRL-Fas lpr mice can induce GN and cryoglobulinemia, but the features that confer nephritogenic potential are not completely understood. Asparagine-linked oligosaccharide chains of 6-19 IgG3 mAb are poorly galactosylated and hardly sialylated, possibly contributing to the pathogenic potential of 6-19 IgG3 rheumatoid factors. Here, we used the 6-19 model of cryoglobulin-associated GN to define the relative contributions of galactosylation and sialylation, in relation to cryoglobulin activity, to the nephritogenic potential of IgG3 antibodies. We generated one highly sialylated and two distinct more galactosylated 6-19 IgG3 rheumatoid factor variants. Although the mere extent of galactosylation had no effect on either the cryogenic and nephritogenic activities of 6-19 IgG3 rheumatoid factor, terminal sialylation attenuated the nephritogenic potential of 6-19 IgG3 by limiting its cryoglobulin activity. These data suggest a protective role of IgG sialylation against the development of cryoglobulin-mediated GN, highlighting the anti-inflammatory activity of sialylated IgG antibodies. Cryoglobulins are a heterogeneous group of Igs that precipitate at temperatures ,37°C, with resolution upon warming. 1,2 Most cryoglobulins are either monoclonal Ig or Ig complexes in which one component, usually IgM, has rheumatoid factor (RF) activity. 1,2 Monoclonal cryoglobulins are mainly associated with various lymphoproliferative disorders, whereas mixed cryoglobulins are often found in sera of patients with autoimmune diseases, such as SLE and rheumatoid arthritis, or with chronic infectious diseases. The presence of cryoglobulins can result in a wide range of vascular, renal, and neurologic complications, likely depending on their concentration, their temperature-dependent solubility behavior, and the nature and type of proteins involved. 2 Antibodies of the IgG3 subclass in humans and mice have the unique physicochemical property that allows them to self-associate via Fc-Fc interactions and to display cryoglobulin activity, independently of their specificities. [3][4][5][6][7][8] Nucleotide sequence analysis of the variable regions of cryogenic and noncryogenic IgG3 mAbs, in combination with the assessment of mutant antibodies, showed that cryoglobulin activity of IgG3 was associated with the presence of more positively charged amino-acid residues at positions 6 and 23 of the heavy-chain variable domain. 9,10 Moreover, structural analysis of asparagine-linked biantennary complex-type oligosaccharide chains (N-glycans) attached to the CH2 domain of different IgG3 mAbs revealed an inverse correlation

Interleukin‐21 Receptor Blockade Inhibits Secondary Humoral Responses and Halts the Progression of Preestablished Disease in the (NZB × NZW)F1 Systemic Lupus Erythematosus Model

“…This finding is consistent with a previous description of IL-21 as an IgG3 switch factor (19). IL-21-driven IgG3 class switching may play a pathogenic role in the NZB/NZW mouse model of lupus, as other efficacious therapies specifically reduce self-reactive IgG3, an isotype which can be particularly nephritogenic (20)(21)(22). In light of several studies describing disease inhibition in IL-21or IL-21R-knockout mice, our results demonstrate that IL-21 is important for both the initiation and maintenance of autoimmune inflammation.…”

Different biochemical patterns in type II and type III mixed cryoglobulinemia in HCV positive patients

“…Key factors are probably chronic stimulation of the immune system through HCV infection, and the dysfunction of the reticuloendothelial system [21], thereby leading to the production and persistence of antibodies that are able to precipitate below body temperature [22]. There is a higher prevalence of IgG3 responses to HCV antigens in HCV-related MC patients than in HCV patients without MC [23].…”

Integrin β1 Promotes the Interaction of Murine IgG3 with Effector Cells

“…The mIgG3 isotype is enriched during murine humoral response to carbohydrate Ags (13,14). Additionally, mIgG3 frequently behaves as a cryoglobulin, being involved in autoimmune diseases such as glomerulonephritis or lupus-like skin lesions in mice (15)(16)(17). Technological interest in the mIgG3 isotype is marginal because mIgG3 mAbs are prone to aggregation as a result of intermolecular C region interactions (18), which decreases production efficiency, stability, and safety.…”