Katherine Bodman

Changes in IgG glycoform levels are associated with remission of arthritis during pregnancy

It was found that the percentage of IgG-associated agalactosyl N-linked oligosaccharides (G0) falls during normal human pregnancy and rises to values higher than before conception following delivery (n = 10, 39-55 days after delivery). Serial bleeds from a normal pregnant woman showed a fall in the percentage G0 during gestation and a rapid rise post-partum. A similar study on a pregnant arthritic woman with a pathologically elevated percentage G0 also showed a fall in percentage G0 during pregnancy and a rapid rise post-partum. The changes in IgG glycosylation in the pregnant arthritic woman occurred simultaneously with the pregnancy-induced remission and post-partum recurrence of disease. A further seven pregnant women with rheumatoid arthritis were studied and analysis of their G0 values pre- and post-partum confirmed the result. In a further series of experiments using an animal model of rheumatoid arthritis, DBA/1 mice with collagen-induced arthritis were found to have elevated G0 levels compared with control mice. The percentage G0 was found to fall simultaneously with pregnancy-induced remission to the same value as non-arthritic pregnant mice. Post-partum recurrence of arthritis in these mice was also accompanied by a simultaneous and rapid rise in percentage G0. Pseudopregnancy did not result in a change in the percentage G0, confirming the effect of true pregnancy. Since the proportion of agalactosyl IgG is abnormally high in the serum of patients with rheumatoid arthritis these changes in IgG glycoform levels, or the factors which control them, may be related to the mechanisms underlying remission of arthritis in humans during pregnancy.

Analysis of glycosylation changes in IgG using lectins

A simple rapid assay based on the ability of lectins to bind carbohydrates has been developed to analyse changes in the oligosaccharide chains of IgG. Bandeiraea simplicifolia lectin and Ricinus communis agglutinin have been used to detect terminal N-acetylglucosamine and galactose moieties respectively in IgG using immunodot-blotting. IgG samples (approximately 1 micrograms) were dot-blotted onto nitrocellulose followed by boiling of the blots to expose the carbohydrate moieties. The blots were then treated with biotinylated lectins followed by either streptavidin-biotin-hydrogen peroxidase conjugate or 125I-labelled streptavidin. The colour was developed using chloronaphthol and the blots read on a densitometer. The labelled blots were cut and read on a gamma counter. The use of a monoclonal antibody to N-acetylglucosamine is also discussed. The results obtained using this method are comparable to those obtained by structural analysis.

The forces driving autoimmune disease.

There are two classes of autoimmune disease, organ-specific and non-organ specific or systemic. That cells producing autoantibodies are selected by antigen is strongly suggested by the presence of mutations and high affinity antibody. T-cells are pivotal in all forms of autoimmunity as evidenced by the therapeutic benefit of anti-T-cell monoclonals such as anti-CD4, and the frequent development of high affinity IgG autoantibodies. The production of anergic T-cells by the use of non-depleting anti-CD4 in the presence of antigen is discussed with particular reference to its potential for immunological intervention in autoimmune disease. It is possible to identify T-cell epitopes in organ-specific autoimmunity using pathogenic T-cell clones or hybridomas to identify the peptide sequences which are reactive. Antigen-specific therapy may ultimately be based on such peptide epitopes. The specificity of the T-cells in systemic autoimmunity is still obscure, but there is some evidence that reactivity with certain germ-line idiotypes can lead to the development of systemic autoimmunity. The possibility of stimulating B-cells specific for auto-antigens such as DNA becomes feasible if a complex of antibody and DNA is taken up by these specific B-cells and processed idiotype is presented to T-helpers specific for those idiotype epitopes. Evidence is presented that there may be pre-existing defects in the target organ in certain organ-specific disorders, and the evidence for a glycosylation defect in the IgG in patients with rheumatoid arthritis is explored. It is noted that the spouses of probands with rheumatoid arthritis is explored. It is noted that the spouses of probands with rheumatoid arthritis also tend to have this glycosylation defect and this raises the possibility of an effect due to an environmental factor, such as a microbial infection. Molecular mimicry of autoantigens by microbes can stimulate autoreactive cells by their cross-reactivity. It is emphasized that cross-reaction which gives rise to the priming of autoreactive T-cells could give rise to the establishment of a chronic autoimmune state. In animals with normal regulatory immune systems, such induced autoimmunity is ultimately corrected and it is only in animals where there are defects in regulation, that autoimmunity persists. Thus, there are many factors giving rise to autoimmunity, and the diseases are rightly regarded as multifactorial in origin.

THE ROLE OF ANTIGEN IN AUTOIMMUNE RESPONSES WITH SPECIAL REFERENCE TO CHANGES IN CARBOHYDRATE STRUCTURE OF IGG IN RHEUMATOID-ARTHRITIS

Abstract Evidence indicating an important role for antigen in the provocation of autoimmune responses is presented. Attention is especially focused on carbohydrate abnormalities in IgG in rheumatoid arthritis, since autosensitization to this molecule is thought to be of central importance in the pathogenesis of this disease. A higher percentage of Fcγ oligosaccharide chains in the serum IgG of patients with rheumatoid arthritis lack terminal galactose residues relative to age-matched controls. This does not appear to be a characteristic feature of chronic inflammatory diseases in general. A new, more rapid assay for agalactosyl chains is described and shown to give results comparable to the more conventional biochemical analysis. The defect probably arises from a reduction in activity of B-cell galactosyltransferases. The galactose changes may contribute to the autoantigenicity of IgG and could facilitate the self-association of IgG rheumatoid factors.

Lymphocytes from patients with rheumatoid arthritis produce agalactosylated IgG in vitro

The percentage of oligosaccharide chains lacking galactose was measured in IgG obtained from pokeweed mitogen‐activated cultures of blood lymphocytes from patients with rheumatoid arthritis and controls. Secreted IgG from rheumatoid arthritis lymphocytes was deficient in galactose compared with IgG from the lymphocytes of controls. This confirms that agalactosylation is a significant feature of the disease and demonstrates that it can occur at the B cell level and is not merely a post‐secretory event.

IGG GLYCOSYLATION IN AUTOIMMUNE-PRONE STRAINS OF MICE

The relationship between increased levels of IgG oligosaccharide chains lacking galactose (GO) and the development of rheumatoid arthritis is unclear. In order to further our understanding of the observed correlation between raised serum GO and arthritis, we have studied GO levels in arthritis prone and non‐susceptible (i.e., non‐arthritis‐prone) mice and the effects on GO of mycobacterial antigens, which have been postulated to play a role in the early events leading to the development of arthritis. We have shown that different age‐matched mouse strains have characteristic “resting” levels of GO which (in six out of seven strains of mice) increase with age. We have also shown that these increases can be enhanced by immunization of arthritis‐prone strains of mice with an adjuvant containing mycobacteria (Freunds complete adjuvant (FCA)), suggesting that deflects in the ability to regulate these GO changes may be related to susceptibility to arthritis.

The Role of Antigen in Autoimmune Responses with Special Reference to Changes in Carbohydrate Structure of IgG in Rheumatoid Arthritis

Evidence indicating an important role for antigen in the provocation of autoimmune responses is presented. Attention is especially focused on carbohydrate abnormalities in IgG in rheumatoid arthritis, since autosensitization to this molecule is thought to be of central importance in the pathogenesis of this disease. A higher percentage of Fcγ oligosaccharide chains in the serum IgG of patients with rheumatoid arthritis lack terminal galactose residues relative to age-matched controls. This does not appear to be a characteristic feature of chronic inflammatory diseases in general. A new, more rapid assay for agalactosyl chains is described and shown to give results comparable to the more conventional biochemical analysis. The defect probably arises from a reduction in activity of B-cell galactosyltransferases. The galactose changes may contribute to the autoantigenicity of IgG and could facilitate the self-association of IgG rheumatoid factors.