Abnormalities in the glycosylation of IgG in spouses of patients with rheumatoid arthritis. A family study

State of the art in childhood nephrotic syndrome: concrete discoveries and unmet needs

Nephrotic syndrome (NS) is a clinical entity characterized by proteinuria, hypoalbuminemia, and peripheral edema. NS affects about 2-7 per 100,000 children aged below 18 years old yearly and is classified, based on the response to drugs, into steroid sensitive (SSNS), steroid dependent, (SDNS), multidrug dependent (MDNS), and multidrug resistant (MRNS). Forms of NS that are more difficult to treat are associated with a worse outcome with respect to renal function. In particular, MRNS commonly progresses to end stage renal failure requiring renal transplantation, with recurrence of the original disease in half of the cases. Histological presentations of NS may vary from minimal glomerular lesions (MCD) to focal segmental glomerulosclerosis (FSGS) and, of relevance, the histological patterns do not correlate with the response to treatments. Moreover, around half of MRNS cases are secondary to causative pathogenic variants in genes involved in maintaining the glomerular structure. The pathogenesis of NS is still poorly understood and therapeutic approaches are mostly based on clinical experience. Understanding of pathogenetic mechanisms of NS is one of the 'unmet needs' in nephrology and represents a significant challenge for the scientific community. The scope of the present review includes exploring relevant findings, identifying unmet needs, and reviewing therapeutic developments that characterize NS in the last decades. The main aim is to provide a basis for new perspectives and mechanistic studies in NS.

The immunomodulatory action of dexamethasone on monoclonal antibody-producing hybridoma cells

As found in different studies, glucocorticoid hormones (GCs) as well as interleukin-6 (IL-6) are involved in the modulation of protein glycosylation. In this work we have investigated the immunomodulatory effect of dexamethasone by assessing in vitro IgG glycosylation by monoclonal antibody-producing hybridoma cells. As described in myeloma cell lines, cellular viability and proliferation rates of hybridoma 112D5 cells decrease when cultured with dexamethasone during 24 hours, in a dose-dependent way. Moreover, the corticosteroid triggered apoptosis of the hybridoma, which was observed as soon as 4 h after culturing cells in the presence of the drug. In line with these results, after 24 h, dexamethasone induced a drop in the anti-DNP level of antibodies synthesized by hybridoma 112D5. In previous works we described that asymmetric glycosylation of in vitro synthesized IgG correlated with induction of cell damage. Nevertheless, an increase in asymmetric IgG glycosylation was not observed here, but there was a decrease in the proportion of asymmetrically glycosylated IgG synthesized by the hybridoma after a 4-h culture with the drug. Finally, as results from assessing IL-6 production by ELISA, we conclude that the above described effects of dexamethasone on hybridoma 112D5 cells could not be due to the inhibition of IL-6 synthesis exerted by the corticoid but rather to a direct effect of the drug. Monoclonal antibody (MAb) producing hybridomas provide an excellent in vitro model for the study of the molecular mechanisms involved in immunoglobulin glycosylation.

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.

IgG3 reactive rheumatoid factor in rheumatoid arthritis: etiologic and pathogenic considerations

Rheumatoid factor (RF) is a polyclonal autoantibody directed against the Fc portion of IgG. Although the role of RF in patients with rheumatoid arthritis (RA) is unclear, immune complexes that form between RF and IgG can activate the classical complement (C) pathway, leading to pathogenic outcomes involving inflammatory events and tissue damage. The specificity of serum RF and RF produced by rheumatoid synovial cells (RSC) is different. Serum RF has specificity for rabbit IgG and human IgG subclasses IgG1, 2, and 4, but binds poorly to IgG3. The affinity of serum RF for IgG Fc is low, having an association constant of 10(4)-10(5) M-1. RSC RF, however, has specificity for human IgG and high avidity for IgG3. Because of this greater specificity and avidity for IgG3, and because RSC RF may be pathogenically more important than serum RF, an important role for IgG3-reactive RF in RA may exist. Binding of RF to IgG may be dependent on the allotype and glycosylation of IgG. Infectious agents present in RA patients may directly or indirectly induce the production of certain RF. In this communication, we review and expand on several observations examining the role of IgG3-reactive RF in RA including: 1) binding differences between RF derived from RSC and serum; 2) glycosylation characteristics of IgG and its interaction with RF; 3) apparent allotype dependent binding of IgG3-reactive RF; and 4) possible relationship between infectious agents and the production of IgG3-reactive RF. Taken together, these observations suggest an important role for IgG3-reactive RF in better understanding the etiology and pathogenesis of RA.

Rheumatoid arthritis: how well do the theories fit the evidence?

In this brief review, inspired partly by a symposium at the autumn meeting of the British Society for Immunology, 1992, varying hypotheses concerning the etiopathogenesis of rheumatoid arthritis (RA) are explored and tested against current evidence. Immunogenetic considerations, whilst of interest, have not aided our understanding of the development of this disease. The association with restricted HLA-DR beta chain hypervariable sequences does not hold true with all cases of RA (but may be related to disease severity) and studies of T cell receptor (TCR) beta chain usage fail to show consistent oligoclonality of infiltrating T cells in the synovial compartment. Etiologies based on triggering by bacteria are also considered: homologies between the 'shared epitope' sequences of HLA-DR1 and DR4 beta chains, Escherichia coli dnaJ and Proteus haemolysin do not indicate any feasible mechanisms for the development of RA, and cannot explain the many cases in which such DR sequences do not occur, though new data from man and animals enhance interest in the role of bowel flora. Finally, the striking parallels between slow bacterial infections and RA, in terms of immunogenetics, pathology, IgG glycosylation abnormalities and autoimmune manifestations, are put forward as circumstantial evidence that such bacterial infections may underly, or trigger, this serious disease.

Second Jenner international glycoimmunology meeting

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Abnormal galactosylation of serum IgG in patients with systemic lupus erythematosus and members of families with high frequency of autoimmune diseases

Gas chromatographic carbohydrate analyses of IgG from 30 patients with idiopathic systemic lupus erythematosus (SLE) revealed lower content of galactose when compared to that in 36 controls of similar ages (mean +/- SD, 3.18 +/- 0.66 vs 3.82 +/- 0.41 galactose residues/mole of IgG, P < 0.001). Abnormal galactosylation was observed in 60% of SLE patients. Analyses of IgG from 58 members of five families, characterized by a high frequency of SLE and other autoimmune diseases and serological abnormalities, and 51 controls of similar age range revealed that IgG galactose deficiency was detectable not only in some members with clinical and serological abnormalities (P < or = 0.001), but also in those without evidence of autoimmune diseases or abnormal serologies (P < or = 0.001). These data indicate that abnormal galactosylation of IgG frequently occurs in asymptomatic members of families with a high frequency of SLE and other autoimmune diseases and suggests that this abnormality may be an indicator for the development of these diseases.