Occurrence of deficient galactosylation of serum IgG prior to the onset of rheumatoid arthritis

Immunoglobulin G N-glycan Biomarkers for Autoimmune Diseases: Current State and a Glycoinformatics Perspective

The effective treatment of autoimmune disorders can greatly benefit from disease-specific biomarkers that are functionally involved in immune system regulation and can be collected through minimally invasive procedures. In this regard, human serum IgG N-glycans are promising for uncovering disease predisposition and monitoring progression, and for the identification of specific molecular targets for advanced therapies. In particular, the IgG N-glycome in diseased tissues is considered to be disease-dependent; thus, specific glycan structures may be involved in the pathophysiology of autoimmune diseases. This study provides a critical overview of the literature on human IgG N-glycomics, with a focus on the identification of disease-specific glycan alterations. In order to expedite the establishment of clinically-relevant N-glycan biomarkers, the employment of advanced computational tools for the interpretation of clinical data and their relationship with the underlying molecular mechanisms may be critical. Glycoinformatics tools, including artificial intelligence and systems glycobiology approaches, are reviewed for their potential to provide insight into patient stratification and disease etiology. Challenges in the integration of such glycoinformatics approaches in N-glycan biomarker research are critically discussed.

Tertiary Lymphoid Structures: Autoimmunity Goes Local

Tertiary lymphoid structures (TLS) are frequently observed in target organs of autoimmune diseases. TLS present features of secondary lymphoid organs such as segregated T and B cell zones, presence of follicular dendritic cell networks, high endothelial venules and specialized lymphoid fibroblasts and display the mechanisms to support local adaptive immune responses toward locally displayed antigens. TLS detection in the tissue is often associated with poor prognosis of disease, auto-antibody production and malignancy development. This review focuses on the contribution of TLS toward the persistence of the inflammatory drive, the survival of autoreactive lymphocyte clones and post-translational modifications, responsible for the pathogenicity of locally formed autoantibodies, during autoimmune disease development.

Heterogeneity of O-glycosylation in the hinge region of human IgA1

Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry was applied to studies of the molecular heterogeneity of desialylated human IgA1 hinge region glycopeptides released with two IgA1 proteases. Typically, the hinge region of an alpha1 chain contains three to five O-linked glycan chains. Variants of the hinge region peptides released from IgA1(Kni) myeloma protein carrying 0, 1, 2, or 3 GalNAc residues were observed in the mass spectra as well as the nonglycosylated peptide. Variable numbers of Gal residues indicated additional heterogeneity in O-glycosylation of IgA1. In the hinge region preparation from normal human serum IgA1, glycopeptides carrying 2, 3, 4, or 5 GalNAc residues with variable numbers of Gal residues were detected. In conclusion, our new approach using the site-specific cleavage with two IgA1 proteases allowed precise and sensitive MALDI-TOF mass spectrometric analysis of O-glycosylation heterogeneity in IgA1 hinge region.

Does it take sugar? A clinical role for measuring the glycosylation of IgG?

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Glycosylation of IgG during potentially arthritogenic lentiviral infections

Agalactosyl IgG [Gal(0)] was first discovered in patients with rheumatoid arthritis (RA). However, the proportion of this glycoform is also raised in tuberculosis and leprosy. This has helped reinforce the suggestion that RA may be triggered by a mycobacterium-like slow bacterial infection. On the other hand, arthritis can occur in mycobacterial diseases, so raised Gal(0) could be associated with a tendency to arthritis, rather than with a particular type of infection. Therefore, we wished to find out whether the percentage of Gal(0) [%Gal(0)] is increased in sheep and goats following infection with maedi visna virus or caprine arthritis encephalitis virus (CAEV), both of which can lead to inflammatory synovitis. We found that the normal level of Gal(0) in these species is much lower than in humans. Goats infected with CAEV or Mycobacterium paratuberculosis (used as a control mycobacterial infection) had a significant increase in %Gal(0), though it was still below the level seen in normal humans. Studies by Western blot confirmed the presence of terminal N-acetylglucosamine on heavy chains, and percentages of Gal(0) comparable to those seen in human RA could be generated by exposing goat IgG to streptococcal beta-galactosidase. The rise in %Gal(0) was greatest in members of infected herds that were just starting to manifest arthritis, and tended to be lower in those in which severe carpitis had developed at the time of bleeding, implying the possibility that raise %Gal(0) may be an early or predisposing event for the development of arthritis.(ABSTRACT TRUNCATED AT 250 WORDS)

Abnormalities in the glycosylation of IgG and its clinical utility

It is approximately ten years since the first detailed analysis of the variation in oligosaccharide structures attached to human serum IgG was published [1]. This study also showed that the percentage incidence of agalactosyl structures on the bi-antennary oligosaccharide complex linked to the Fc region, was increased in patients with rheumatoid arthritis. An earlier study [2], published in abstract from only, had also suggested that this was the case but was never followed up. In this review the considerable amount of work that has explored the clinical relevance of abnormalities in the glycosylation of IgG is analysed critically.

Expression of rheumatoid factor idiotypes 17.109, 6B6.6 and 4C9 in the sera of Pima Indians

This study was undertaken to determine whether the expression of 17.109, 6B6.6 and 4C9 rheumatoid factor (RF) idiotypes is predictive of the development of rheumatoid arthritis (RA) and whether the RF response is idiotypically restricted in an inbred population of Pima Indians who have a genetic predisposition for the disease. Serial sera were obtained from 25 subjects who developed RA and 25 RF-positive subjects who did not develop RA over the course of a longitudinal community health survey. RF titers and titers of the RF-associated idiotypes 17.109, 6B6.6 and 4C9 were determined by ELISA, and the relationship between 6B6.6 and 4C9 was analyzed by cross-absorption studies. Expression of the three RF-associated idiotypes was found in both the subjects who developed RA and those who did not. The amount of idiotype expressed was variable, but a few subjects in both groups had high levels indicative of an oligoclonal RF response. Reactivity with 6B6.6 and 4C9 antiidiotypes overlapped, with 4C9 appearing to mark a broader spectrum of RF than 6B6.6. Thus, even in an inbred and genetically predisposed population, the RF-associated antiidiotypes studied here did not identify a dominant idiotypic response and were no better markers for the development of RA than was RF itself.