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

Antibody-mediated rejection: emergence of animal models to answer clinical questions

Decades of experiments in small animals had tipped the balance of opinion away from antibodies as a cause of transplant rejection. However, clinical experience, especially with sensitized patients, has convinced basic immunologists of the need to develop models to investigate mechanisms underlying antibody-mediated rejection (AMR). This resurgent interest has resulted in several new rodent models to investigate antibody-mediated mechanisms of heart and renal allograft injury, but satisfactory models of chronic AMR remain more elusive. Nevertheless, these new studies have begun to reveal many insights into the molecular and pathological sequelae of antibody binding to the allograft endothelium. In addition, complement-independent and complement-dependent effects of antibodies on endothelial cells have been identified in vitro. As small animal models become better defined, it is anticipated that they will be more widely used to answer further questions concerning mechanisms of antibody-mediated tissue injury as well as to design therapeutic interventions.

Is IgG galactosylation the relevant factor for pregnancy-induced remission of rheumatoid arthritis?

During pregnancy, most patients with rheumatoid arthritis (RA) experience spontaneous improvement of their disease activity. Among the soluble candidates that have been investigated in search for the most relevant disease-remitting factor are the galactosylation levels of immunoglobulin G (IgG). In RA, a higher percentage of IgG lacking the terminal galactose residues, thought to play a pro-inflammatory role, is found. During pregnancy, however, IgG galactosylation levels increase and correlate with improved disease activity. The question remains whether the increase in IgG galactosylation during pregnancy is a mere epiphenomenon or a true remission-inducing factor.

Impact of Glycosylation on Effector Functions of Therapeutic IgG

Human IgG has only one conserved glycosylation site located in the Cγ2 domain of the Fc region that accounts for the presence of two sugar moieties per IgG. These IgG sugar cores play a critical role in a number of IgG effector functions. In the present review, we describe the main characteristics of IgG Fc glycosylation and some abnormalities of serum IgG glycosylation. We also discuss how glycosylation impacts on monoclonal antibodies (mAbs) and IVIg effector functions and how these molecules can be engineered. Several therapeutic antibodies have now been engineered to be no- or low-fucose antibodies and are currently tested in clinical trials. They exhibit an increased binding to activating FcγRIIIA and trigger a strong antibody-dependent cell cytotoxicity (ADCC) as compared to their highly-fucosylated counterparts. They represent a new generation of therapeutic antibodies that are likely to show a better clinical efficacy in patients, notably in cancer patients where cytotoxic antibodies are needed.

FcγRs in health and disease

Genetic defects affecting the humoral immune response and especially the production of antibodies of the immunoglobulin G (IgG) isotype result in a heightened susceptibility to infections. Studies over the last years have demonstrated the crucial role of Fc-receptors for IgG (FcγRs) widely expressed on innate immune effector cells in mediating the protective function of IgG. During the last years, additional ligands interacting with FcγRs as well as additional receptors binding to IgG glycosylation variants have been identified. In this review, we discuss how the interaction of these different ligands with classical and novel Fcγ-receptors influences the immune response and which strategies microorganisms have developed to prevent them.

Immunoglobulin G galactosylation and sialylation are associated with pregnancy-induced improvement of rheumatoid arthritis and the postpartum flare: results from a large prospective cohort study

Introduction

Improvement of rheumatoid arthritis (RA) during pregnancy has been causatively associated with increased galactosylation of immunoglobulin G (IgG) N-glycans. Since previous studies were small, did not include the postpartum flare and did not study sialylation, these issues were addressed in the present study.

Methods

Serum from 148 RA cases and 32 healthy controls was collected at several time points before, during and after pregnancy. Improvement during pregnancy and postpartum flare were determined according to the European League Against Rheumatism (EULAR) response criteria. Galactosylation and sialylation of Immunoglobulin G (IgG) and the presence of bisecting N-acetylglucosamine (GlcNAc) were analyzed by matrix-assisted laser desorption/ionization - time of flight - mass spectrometry (MALDI-TOF-MS).

Results

IgG1 and IgG2 galactosylation of the cases and controls increased during pregnancy with a maximum in the third trimester. Galactosylation decreased directly postpartum. IgG galactosylation of controls was at a higher level than cases (P < 0.001 at all time points) and a similar pattern was observed for sialylation. Moreover, there was a good association between galactosylation and sialylation. The increase in galactosylation was significantly more pronounced for cases with improvement than cases without improvement during pregnancy. The reverse was true for deteriorators and non-deteriorators postpartum. The presence of bisecting GlcNAc was not significantly influenced by pregnancy or postpartum for cases and controls.

Conclusions

This large cohort study demonstrates the association of changes in galactosylation with both pregnancy-induced improvement and postpartum flare in RA-patients, suggesting a role for changes in glycosylation in the pregnancy-induced improvement of RA.

Regulated glycosylation patterns of IgG during alloimmune responses against human platelet antigens

Various biological activities of immunoglobulin G (IgG) including antibody-dependent cellular cytotoxicity (ADCC) are modulated by the structural features of the N-glycans in the Fc part. In this study, we describe a population of IgG1 alloantibodies which are formed during pregnancy against human platelet antigens (HPA) of the fetus, causing fetoneonatal alloimmune thrombocytopenia. By analyzing the Fc-glycosylation of the pathogenic, affinity-purified IgG1 alloantibodies at the glycopeptide level using mass spectrometry, we found markedly decreased levels of core-fucosylation as well as increased levels of galactosylation and sialylation as compared to glycosylation patterns of total serum IgG1 of the same patients. Because IgG1 Fc-core-fucosylation is known to influence ADCC activity, modulation of core-fucosylation may have a profound effect on disease severity and prognosis. Studies in large patient cohorts will have to be performed to establish such correlations. Moreover, experiments in animal models as well as in vitro immunological tests will be needed to unravel the mechanisms regulating IgG Fc glycosylation.

Sialic acid residues are essential for the anaphylactic activity of murine IgG1 antibodies

Glycosylation of the Ab molecule is essential for maintaining the functional structure of Fc region and consequently for Ab-mediated effector functions, such as binding to cells or complement system activation. Alterations in the composition of the sugar moiety can dramatically influence Ab activity; however, it is not completely clear how differences in the N-linked oligosaccharide structure impact the biological function of Abs. We have described that murine IgG1 Abs can be separated according to their ability to elicit in vivo anaphylaxis in a fraction of anaphylactic and other of non-anaphylactic molecules. Furthermore, we showed that the N-linked oligosaccharide chain is essential for the structural conformation of the anaphylactic IgG1, the binding to FcgammaRIII on mast cells, and, consequently, for the ability to mediate anaphylactic reactions. In this study, we evaluated the contribution of individual sugar residues to this biological function. Differences in the glycan composition were observed when we analyzed oligosaccharide chains from anaphylactic or non-anaphylactic IgG1, mainly the presence of more sialic acid and fucose residues in anaphylactic molecules. Interestingly, the enzymatic removal of terminal sialic acid residues in anaphylactic IgG1 resulted in loss of the ability to trigger mast cell degranulation and in vivo anaphylactic reaction, similarly to the deglycosylated IgG1 Ab. In contrast, fucose removal did not affect the anaphylactic function. Therefore, we demonstrated that the ability of murine IgG1 Abs to mediate anaphylaxis is directly dependent on the amount of sialic acid residues associated to the oligosaccharide chain attached to the Fc region of these molecules.

Evaluation of the serum N-linked glycome for the diagnosis of cancer and chronic inflammation

The identification of serum biomarkers has lead to improvements in the detection and diagnosis of cancer, and combinations of these biomarkers have increased further their sensitivity and specificity. Glycosylation is the most common PTM of secreted proteins and the identification of novel serum glyco-biomarkers has become a topic of increasing interest because the glycan processing pathways are frequently disturbed in cancer cells. A future goal is to combine current biomarkers with glyco-biomarkers to yield further improvements. Well characterised N-glycosylation changes in the serum glycome of cancer patients include changes in the levels of tri- and tetra-antennary glycan structures, sialyl Lewis X epitopes and agalactosylated bi-antennary glycans. Several of these glycosylated markers have been linked to chronic inflammatory diseases, promoting questions about the links between inflammation and cancer. In this review, the glycoproteins which display these glycan epitopes, the glycosyl transferases which can generate them, their potential functions and their use as biomarkers are evaluated.

Immunoglobulin 1 (IgG1) Fc-glycosylation profiling of anti-citrullinated peptide antibodies from human serum

In several autoimmune disorders, including rheumatoid arthritis (RA), autoantibodies are thought to be the driving force of pathogenicity. Glycosylation of the Fc-part of human Igs is known to modulate biological activity. Hitherto, glycosylation of human IgG-Fc has been analyzed predominantly at the level of total serum IgG, revealing reduced galactosylation in RA. Given the pathogenic relevance of autoantibodies in RA, we wished, in the present study, to address the question whether distinct Fc-glycosylation features are observable at the level of antigen-specific IgG subpopulations. For this purpose, we have developed a method for the microscale purification and Fc-glycosylation analysis of anti-citrullinated peptide antibodies (ACPA). ACPA represent a group of autoantibodies that occur with unique specificity in RA patients. Their presence is associated with increased inflammatory disease activity and rapid joint destruction. Results indicate that ACPA of the IgG1 subclass vary considerably from total serum IgG1 with respect to Fc-galactosylation, with galactosylation being higher on ACPA than on serum IgG1 for some patients, while other patients show higher galactosylation on serum IgG1 than on ACPA. Using this method, studies can be performed on the biological and clinical relevance of ACPA glycosylation within RA patient cohorts.

Anti-inflammatory actions of intravenous immunoglobulin

The remarkable success story of the therapeutic application of pooled immunoglobulin G (IgG) preparations from thousands of donors, the so-called intravenous IgG (IVIG) therapy, to patients with a variety of hematological and immunological disorders began more than half a century ago. Since then, the use of this primary blood product has increased constantly, resulting in the serious danger of shortages in supply. Despite its widespread use and therapeutic success, the mechanisms of action, especially of the anti-inflammatory activity, are only beginning to be understood. In this review, we summarize the clinical use of IVIG for different diseases and discuss recent data on the molecular mechanisms that might explain how this potent drug mediates its activity in vivo.

Glycosylation profiling of immunoglobulin G (IgG) subclasses from human serum

All four subclasses of human serum IgG contain a single N-glycosylation site in the constant region of their heavy chain, which is occupied by biantennary, largely core-fucosylated and partially truncated oligosaccharides, that may carry a bisecting N-acetylglucosamine and sialic acid residues. IgG glycosylation has been shown to be altered under various physiological and pathological circumstances. IgG N-glycan profiles vary with age, and galactosylation for example is enhanced during pregnancy. Several diseases including rheumatoid arthritis are associated with a reduction in galactosylation of the IgG N-glycans. Here, we describe a robust method for the isolation of IgG subclasses using protein A (binds IgG1, IgG2, and IgG4) and protein G (binds additionally IgG3) at the 96-well plate level, which is suitable for automation. Isolated IgGs were digested with trypsin, and obtained glycopeptides were analyzed by nano-LC-MS. Glycopeptides were characterized by CID as well as electron transfer dissociation (ETD). The method provided glycosylation profiles for IgG1, IgG2, IgG3, and IgG4 and revealed distinct differences in N-glycosylation between the four IgG subclasses. The changes in galactosylation associated with rheumatoid arthritis could readily be monitored. This method is suitable for the subclass-specific analysis of IgG glycosylation from clinical samples.

Immune regulation by B cells and antibodies a view towards the clinic

B lymphocytes contribute to immunity in multiple ways, including production of antibodies, presentation of antigen to T cells, organogenesis of secondary lymphoid organs, and secretion of cytokines. Recent clinical trials have shown that depleting B cells can be highly beneficial for patients with autoimmune diseases, implicating B cells and antibodies as key drivers of pathology. However, it should be kept in mind that B cell responses and antibodies also have important regulatory roles in limiting autoimmune pathology. Here, we analyze clinical examples illustrating the potential of antibodies as treatment for immune-mediated disorders and discuss the underlying mechanisms. Furthermore, we examine the regulatory functions of activated B cells, their involvement in the termination of some experimental autoimmune diseases, and their use in cell-based therapy for such pathologies. These suppressive functions of B cells and antibodies do not only open new ways for harnessing autoimmune illnesses, but they also should be taken into account when designing new strategies for vaccination against microbes and tumors.

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

The glycosylation status of IgG has been implicated in the pathology of rheumatoid arthritis. Earlier, we reported the identification of a novel secreted endo-beta-N-acetylglucosaminidase (EndoS), secreted by Streptococcus pyogenes that specifically hydrolyzes the beta-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 x 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 FcgammaR and disturbed the formation of stable immune complexes. Hence, the asparagine-linked glycan on IgG plays a crucial role in the development of arthritis.

The impact of glycosylation on the biological function and structure of human immunoglobulins

Immunoglobulins are the major secretory products of the adaptive immune system. Each is characterized by a distinctive set of glycoforms that reflects the wide variation in the number, type, and location of their oligosaccharides. In a given physiological state, glycoform populations are reproducible; therefore, disease-associated alterations provide diagnostic biomarkers (e.g., for rheumatoid arthritis) and contribute to disease pathogenesis. The oligosaccharides provide important recognition epitopes that engage with lectins, endowing the immunoglobulins with an expanded functional repertoire. The sugars play specific structural roles, maintaining and modulating effector functions that are physiologically relevant and can be manipulated to optimize the properties of therapeutic antibodies. New molecular models of all the immunoglobulins are included to provide a basis for informed and critical discussion. The models were constructed by combining glycan sequencing data with oligosaccharide linkage and dynamics information from the Glycobiology Institute experimental database and protein structural data from "The Protein Data Bank."

Agalactosylated IgG antibodies depend on cellular Fc receptors for in vivo activity

IgG antibodies are glycoproteins containing a branched sugar moiety attached to the asparagine 297 residue in the antibody constant region (Fc). This glycan is essential for maintaining a functional Fc structure, which is a prerequisite for antibody-mediated effector functions, such as the interaction with cellular Fc receptors or the complement component C1q. Variations in the composition of the sugar moiety can dramatically influence antibody activity. Moreover, humans and mice with autoimmune disorders, such as rheumatoid arthritis, have altered IgG glycosylation patterns with increased levels of antibodies lacking terminal sialic acid and galactose residues (IgG-G0). There is great interest in understanding whether this altered glycosylation pattern influences antibody-mediated effector functions. In vitro studies have suggested that IgG-G0 antibodies gain the capacity to activate the complement pathway via mannose-binding lectin (MBL), which could contribute to antibody-mediated inflammation. We have analyzed the activity of IgG-G0 antibodies in mice with a genetic deletion of MBL (MBL-null mice) and demonstrate that IgG-G0 antibodies are unimpaired in MBL-null mice. In contrast, the activity of these antibody glycovariants is fully dependent on the presence of activating Fc receptors.

Antibody-induced arthritis: disease mechanisms and genes involved at the effector phase of arthritis

During the development of rheumatoid arthritis (RA) autoantibodies to IgG-Fc, citrullinated proteins, collagen type II (CII), glucose 6 phosphoisomerase (G6PI) and some other self-antigens appear. Of these, a pathogenic effect of the anti-CII and anti-G6PI antibodies is well demonstrated using animal models. These new antibody mediated arthritis models have proven to be very useful for studies involved in understanding the molecular pathways of the induction of arthritis in joints. Both the complement and FcgammaR systems have been found to play essential roles. Neutrophils and macrophages are important inflammatory cells and the secretion of tumour necrosis factor-alpha and IL-1beta is pathogenic. The identification of the genetic polymorphisms predisposing to arthritis is important for understanding the complexity of arthritis. Disease mechanisms and gene regions studied using the two antibody-induced arthritis mouse models (collagen antibody-induced arthritis and serum transfer-induced arthritis) are compared and discussed for their relevance in RA pathogenesis.

Antibodies against cyclic citrullinated peptide and IgA rheumatoid factor predict the development of rheumatoid arthritis

OBJECTIVE

To evaluate the prevalence and predictive value of anti-cyclic citrullinated peptide (anti-CCP) antibodies in individuals who subsequently developed rheumatoid arthritis (RA) and to determine the relationship to rheumatoid factor (RF) of any isotype.

METHODS

A case-control study was nested within the Northern Sweden Health and Disease Study and the Maternity cohorts of Northern Sweden. Patients with RA were identified among blood donors whose samples had been taken years before the onset of symptoms. Control subjects matched for age, sex, date of sampling, and residential area were selected randomly from the same cohorts. Anti-CCP antibody and RFs were determined using enzyme immunoassays.

RESULTS

Eighty-three individuals with RA were identified as having donated blood before presenting with any symptoms of joint disease (median 2.5 years [interquartile range 1.1-4.7] before RA). In samples obtained before the onset of RA, the prevalence of autoantibodies was 33.7% for anti-CCP, 16.9% for IgG-RF, 19.3% for IgM-RF, and 33.7% for IgA-RF (all highly significant compared with controls). The sensitivities for detecting these autoantibodies >1.5 years and </=1.5 years before the appearance of any RA symptoms were 25% and 52% for anti-CCP, 15% and 30% for IgM-RF, 12% and 27% for IgG-RF, and 29% and 39% for IgA-RF. In conditional logistic regression models, anti-CCP antibody and IgA-RF were found to be significant predictors of RA.

CONCLUSION

Anti-CCP antibody and RFs of all isotypes predated the onset of RA by several years. The presence of anti-CCP and IgA-RF predicted the development of RA, with anti-CCP antibody having the highest predictive value. This indicates that citrullination and the production of anti-CCP and RF autoantibodies are early processes in RA.

Placental immunomodulator ferritin, a novel immunoregulator, suppresses experimental arthritis

OBJECTIVE

To determine the effect of treatment with C48, the recombinant cytokine-like domain of the novel human placental immunomodulator ferritin (PLIF) immunoregulator, on zymosan-induced arthritis (ZIA) in mice and on adjuvant-induced arthritis (AIA) in rats.

METHODS

The in vitro effect of PLIF/C48 was tested in mixed lymphocyte cultures (MLCs) of allogeneic mouse splenocytes. Arthritis was induced by intraarticular injection of zymosan into naive mice and by subcutaneous injection of Mycobacterium tuberculosis into rats. C48 was injected intraperitoneally daily from day 3 to day 9 or from day 7 to day 13 after induction of synovitis by zymosan, and every other day from day 2 to day 14 after induction of AIA. Swelling of the joints and histologic features of the synovium were assessed. Th1 and Th2 cytokines were quantified by enzyme-linked immunosorbent assay.

RESULTS

Both PLIF and C48 significantly inhibited the in vitro immunoreactivity of mouse splenocytes in MLCs. Treatment of ZIA mice and AIA rats with C48 effectively reduced joint swelling. C48 treatment reduced synovial lining thickening, numbers of mononuclear cells and histiocytes, as well as cartilage destruction and bone erosions. In vitro, activated splenocytes from C48-treated ZIA and AIA animals produced significantly higher levels of interleukin-10 (IL-10). In animals with ZIA, this was accompanied by lower levels of tumor necrosis factor and IL-2.

CONCLUSION

Human PLIF and C48 were shown to exert cross-species immunosuppressive activity in vitro. The in vivo suppression of articular inflammation in the experimental models of ZIA and AIA was the result of treatment with the antiinflammatory human C48. These results suggest that treatment with C48 may offer an effective immunotherapeutic means of controlling inflammatory polyarthritis.

Binding of rheumatoid and lupus synovial fluids and sera-derived human IgG rheumatoid factor to degalactosylated IgG

BACKGROUND

Altered glycosylation of immunoglobulin G (IgG) has been demonstrated in patients with rheumatoid arthritis (RA). Specificity of IgG rheumatoid factor (RF) in recognizing degalactosylated IgG (Fab)(2) and Fc was analyzed in the present study.

METHODS

(Fab)(2) and Fc fragments were prepared from IgG of normal healthy subjects. Enzymes, including peptide-N-glycosidase (PNGase), neuraminidase, and beta-1,4-galactosidase, were used to digest (Fab)(2) and Fc fragments. Binding capacity of IgG RF from patients with RA, systemic lupus erythematosus (SLE), and from healthy subjects to (Fab)(2) and Fc treated with glycosidase, was measured with immunoassay.

RESULTS

Treating (Fab)(2) and Fc with PNGase significantly diminished their binding capacity to IgG RFs. Degalactosylated (Fab)(2) revealed higher affinity to IgG RF in all tested groups. Fc lacking terminal galactose on oligosaccharide chains showed elevated binding with synovial IgG RF of RA patients. However, lesser binding was observed in sera of patients with RA and SLE.

CONCLUSIONS

Our data suggest that IgG molecules containing less terminal galactose on their oligosaccharide moieties are preferentially recognized by IgG RF. Furthermore, IgG RF display alternative binding specificity to degalactosylated (Fab)(2) and Fc in synovial fluids and sera of RA patients.

Thyroid disease in relation to pregnancy: a decade of change

Inspection of the references cited in this review indicates that much work has occurred in the area of thyroid and pregnancy during the last decade. Significant advances in our understanding of the immunology of pregnancy and the effect of thyroid disease on this process have taken place. The role of hCG in the physiology of pregnancy and its relevance to thyroid function has been an emerging theme. There is still no clear explanation for the association between thyroid antibodies and infertility or miscarriage. During the last decade a general concensus has developed in relation to the management of hyperthyroidism in pregnancy although there are still variations in antithyroid drug use at this time. The aetiological classification of congenital hyper- and hypothyroidism utilizing new technologies has opened up a new perspective on these disorders. Attention has been drawn to the importance of treating maternal hypothyroidism with adequate thyroid replacement therapy and to the possibility of impaired child neuropsychological development consequent on low maternal thyroid hormone concentration in early gestation in non iodine deficient areas. Significant advances have been made during the last decade in the description of the clinical features and in our understanding of the pathogenesis of postpartum thyroid disease. The importance of long-term follow up of selected patient groups has also been emphasized.

The effect of lactation in the post-partum arthritis of MRL-lpr/fasmice

OBJECTIVE

To investigate the effects of lactation on the post-partum arthritic flare in MRL-lpr/fas mice.

METHODS

Three groups of mice were investigated. Group 1: females whose litters were weaned at termination of the experiment; group 2: females whose litters were weaned at parturition; group 3: females who were not bred. Clinical evaluation was carried out at 5-day intervals following parturition. Blood samples were also collected during the course of the experiment and assayed for corticosterone and prolactin. Histological evaluation of the joints was assessed at day 30.

RESULTS

The incidence of swelling and erythema, the bimalleolar ankle width and the histopathology were significantly reduced by removal of the litters at parturition. This correlated well with a decrease seen in prolactin levels in these females. Corticosterone, an immunomodulatory glucocorticoid, did not play a significant role in the arthritic flare.

CONCLUSION

Our findings suggest that prolactin levels contribute to the inflammation seen in MRL-lpr/fas mice following parturition.

Pairing of oligosaccharides in the Fc region of immunoglobulin G

The Fc portion of immunoglobulin G (IgG) expresses paired oligosaccharides with microheterogeneities, which are associated with efficiencies of effector functions and with pathological states. A comparison of electrospray ionization mass spectrometry data obtained using a variety of Fc fragments derived from human and mouse IgG that do and do not retain the inter-chain disulfide bridge(s) revealed that (1) the Fc portion can be asymmetric as well as symmetric with respect to glycosylation and (2) the ratios of the individual glycoforms are different from what is expected from the random pairing.

Galactosylation of serum IgG and autoantibodies in murine models of autoimmune haemolytic anaemia

A number of systemic autoimmune diseases are associated with increased levels of the agalactosyl (G0) IgG isoforms that lack a terminal galactose from the CH2 domain oligosaccharide. The current aim was to determine whether the galactosylation of serum IgG is also reduced in a classic antibody-mediated, organ-specific autoimmune condition, and whether the pathogenic autoantibodies are preferentially G0. In two murine forms of autoimmune haemolytic anaemia (AIHA), sera and autoantibodies eluted from erythrocytes were obtained, and the levels of G0 measured using a lectin-binding assay. Serum IgG galactosylation was unaffected following the induction of AIHA in CBA/Igb mice by immunization with rat erythrocytes, but in all animals with the disease the IgG autoantibodies generated were more G0 than the sera. The anti-rat erythrocyte antibodies were similar to the autoantibodies in being preferentially G0, and when CBA/Igb mice were immunized with canine erythrocytes as a control foreign antigen, there was again a bias towards the production of G0 IgG antibodies. In NZB mice with chronic, spontaneous AIHA, the concentration and galactosylation of both serum IgG and autoantibodies were lower than in the induced model, and the ratio of G0 IgG in the serum and erythrocyte eluates varied markedly between different individuals. Our interpretation of these results is that changes in serum IgG or autoantibody galactosylation are not consistent in different models of AIHA, and that production of low galactosyl antibodies can be a feature of a normal immune response.

The thyroid immunology of the postpartum period

Autoimmune thyroid disease (AITD) is suppressed during pregnancy and is exacerbated in the postpartum period. Studies indicate that new-onset AITD occurs in up to 10% of all women in the postpartum period and that up to 60% of Graves' patients in the reproductive years give a history of postpartum onset. Despite this extraordinary epidemiological evidence, the causes of these exacerbations are uncertain and have yet to be adequately investigated. Explaining these postpartum changes, therefore, remains hypothetical. Mechanisms invoked include the passage of fetal cells to the mother during pregnancy establishing maternal microchimerism, pregnancy-induced changes in the thyroid gland itself, and the role of prolactin as a consequence of breast-feeding. Once the disease onset or exacerbation, is established, then there have been considerable advances in our understanding of the immunopathology. Thyroid cell destruction (via apoptosis) or activation (via thyrotropin [TSH] receptor autoantibody induction) appear to be similar to nonpostpartum-related disease. The reasons for the transience in postpartum disease, particularly thyroiditis, is likely to be related to the induction of clonal suicide and the mechanisms for this phenomenon are beginning to be explored. While we have a number of clinical indicators that allow us to predict postpartum thyroid disease (such as autoantibody titers), at present, we have no treatment to prevent the disease. Furthermore, our predictions are not helpful in a high enough proportion of the population to warrant screening of all women before delivery. At this time, the best clinical approach is watchful waiting and postpartum thyroid function testing where suspected.

Sex hormones and pregnancy in rheumatoid arthritis and systemic lupus erythematosus

Rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) are autoimmune disorders with a preponderance in females. RA and SLE differ in their response to sex hormones. Disease development of RA is mitigated by estrogen and pregnancy whereas SLE tends to flare during pregnancy and in response to estrogen. Pregnancy improves the symptoms of RA in about 75% of pregnant patients, but relapses within six months postpartum in 90% of cases. RA is regarded as a T cell-mediated and TH1 immune response-driven disease. Pregnancy induces a shift from TH1 to TH2 immune response, increasing the anti-inflammatory cytokines IL-4 and IL-10, which may contribute to gestational amelioration of RA. Prospective studies of SLE pregnancies indicate that about 50% of patients experience a flare, however, with no permanent aggravation of the disease. Lupus nephritis, presence of antiphospholipid antibodies, and a previous history of pregnancy loss increase the risk of complications during pregnancy and fetal loss. The marked increase of estrogen and progesterone during pregnancy seems to enhance some of the manifestations of SLE. The shift to a TH2 immune response may trigger SLE manifestations that are dependent on humoral immune responses such as lupus nephritis. Another factor stimulating immune responses is the pituitary hormone prolactin, which has been found elevated in SLE patients of both sexes and correlated to disease activity in several studies. The hyperprolactinemia of lactation seems to influence postpartum behavior of SLE as well as RA.

Does rheumatoid arthritis remit during pregnancy and relapse postpartum? Results from a nationwide study in the United Kingdom performed prospectively from late pregnancy

OBJECTIVE

To ascertain the influence of pregnancy on disease activity in women with rheumatoid arthritis (RA) during pregnancy and postpartum.

METHODS

One hundred forty pregnant women were recruited from a nationwide campaign and were followed prospectively in the last trimester and at 1 and 6 months postpartum. Standardized assessment of joint symptoms, examination of inflamed joints, and the Health Assessment Questionnaire (HAQ) were the main measures of disease activity.

RESULTS

There was only a modest fall in HAQ scores during pregnancy, with >25% of women having substantial levels of disability. Other parameters of disease activity showed a greater trend toward improvement, although only 23 (16%) were in complete remission (no joints with active disease and no therapy). Similarly, there was relatively little change in the distribution of HAQ scores from pregnancy to postpartum. There was, however, a statistically significant increase in the mean number of inflamed joints compared with the findings during pregnancy. Analysis of the possible influence of treatment suggested that therapy was associated with more severe disease and was not related to reduction in disease activity.

CONCLUSION

This, the largest prospective study of the influence of pregnancy on RA activity, has demonstrated widespread variability in disease response.

A comparison of in vitro tests for predicting the severity of haemolytic disease of the fetus and newborn

Haemolytic disease of the newborn (HDN) is characterized by the presence of IgG antibodies in the maternal circulation which cause haemolysis in the fetus by crossing the placenta and sensitizing red cells for destruction by macrophages in the fetal spleen. Numerous serological, quantitative and cellular assays have been developed to predict the severity of HDN. These assays all measure and/or characterize alloantibodies in the maternal circulation. Quantitative assays which accurately measure antibody levels correlate with disease severity better than serological assays which are inherently less precise. Nevertheless, high antibody levels are found in some cases of mild HDN and relatively low antibody levels are found in some severe cases. This suggests that disease severity is influenced by factors in addition to antibody concentration. These factors remain to be fully elucidated but may include the subclass and glycosylation of maternal antibodies, the structure, site density, maturational development and tissue distribution of blood group antigens, the efficiency of IgG transport to the fetus, the functional maturity of the fetal spleen, polymorphisms which affect Fc receptor function, and the presence of HLA-related inhibitory antibodies. Cellular assays which are sensitive to factors affecting antibody function have therefore been developed in an attempt to improve the prediction of disease severity. Although these assays are cumbersome, there are now sufficient data to suggest that some cellular assays, when used as part of a structured approach to diagnostic testing, may provide clinically-useful information to complement serological and quantitative assays.

Dissolved oxygen concentration in serum-free continuous culture affects N-linked glycosylation of a monoclonal antibody

The murine B-lymphocyte hybridoma, CC9C10, was grown at steady state in serum-free continuous culture at dissolved oxygen (DO) concentrations of 10, 50, and 100% of air saturation. The secreted mAb, an IgG1, was purified and subjected to both enzymatic deglycosylation using PNGase F and chemical deglycosylation by hydrazinolysis. Both methods resulted in complete removal of N-linked oligosaccharide chains. Isolated N-glycan pools were analyzed by fluorophore-assisted carbohydrate electrophoresis (FACE) and high pH anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD). The FACE profiles and corresponding HPAEC-PAD chromatograms of N-linked oligosaccharides obtained by PNGase F digestion and hydrazinolysis provided complementary and corroborating information. The predominant N-linked structures were core-fucosylated asialo biantennary chains with varying galactosylation. There were also minor amounts of monosialylated, and trace amounts of afucosyl, oligosaccharides. A definite shift towards decreased galactosylation of glycan chains was observed as DO concentration in continuous culture was reduced. The vast majority of N-linked glycosylation occurred on the heavy chain. There was no evidence for N-linked glycosylation of the light chain or for O-linked glycosylation of the mAb.

Fucosylation and galactosylation of IgG heavy chains differ between acute and remission phases of juvenile chronic arthritis

Oligosaccharide structures are attached to nearly all membrane and serum proteins, and their composition changes significantly in many diseases. We have analysed glycosylation of IgG heavy chains in 34 patients with juvenile chronic arthritis and 13 control individuals. IgG was purified from 0.7 ml of serum, separated by electrophoresis and transferred on to polyvinylidene difluoride (PVDF) membrane. Ricinus communis agglutinin (RCA I) and Bandeirea simplicifolia (BSA II) and Ulex europaeus (UEA I) lectins were used to measure galactose, N-acetylglucosamine and fucose, respectively. While there was no significant difference in average levels of galactose and N-acetylglucosamine, patients with juvenile chronic arthritis had 2.4 times more fucose attached to IgG heavy chains than control individuals. A different picture emerged when patients were divided into those with acute disease and those in remission. Patients in whom juvenile chronic arthritis was currently active had significantly lower levels of galactose than those in remission, in whom galactose levels were comparable to the control group. Fucose levels in both groups of patients were significantly higher than in the control group. These results show that whereas de-galactosylation is a good test to detect and measure the activity of juvenile chronic arthritis, increased fucosylation is a much more reliable measure for diagnosis of the disease itself.

Pregnancy and rheumatoid arthritis

Amelioration of rheumatoid arthritis (RA) occurs in about three quarters of pregnancies. Most women who improve experience initial relief in the first trimester. RA almost invariably recurs within 3 to 4 months of delivery. The effect of pregnancy upon the risk of first developing RA is similar in some respects but also differs from that observed in women with established disease. Analogous to women with established disease, the chance of a woman first developing RA is significantly reduced during pregnancy but increased in the first year post partum; thereafter risk is decreased. There is no indication of any adverse effects of RA on pregnancy outcome. Although limited, some medications can be used during pregnancy and during lactation without jeopardizing the well-being of the fetus.

Bias in murine IgG isotype immobilisation. Implications for IgG glycoform analysis ELISA procedures

This study investigates immobilisation of murine IgG in various ELISA procedures. Monoclonal murine IgG isotypes and polyclonal IgG from sera were studied. Similar binding curves to plastic were found for all four individual murine IgG isotypes. Single isotypes displayed different affinities for both protein A and protein G, in particular IgG1 was poorly and IgG3 strongly bound to both of these proteins. When mixtures of the isotypes were bound to either plastic, protein A or protein G, competition was observed in which IgG3 was dominant. Paradoxically, studies on the binding rates of single isotypes direct to plastic revealed that IgG3 had the slowest binding rate. Heating of bound IgGs resulted in significant but isotypically non-selective losses from the plates. The data demonstrate that despite obtaining equivalent individual IgG isotype binding curves, mixtures of IgG isotypes behave very differently, with competition for binding occurring even on plastic. The IgG isotype levels of murine sera were measured for individual mice, and the capture efficiency of each IgG isotype by protein A determined at different serum dilutions. Comparisons were made between the observed capture levels of IgG isotypes and their known serum levels. At all dilutions tested, greater than expected binding of IgG3, IgG2b and IgG2a was observed. At a serum dilution of 1/100 the binding of these three isotypes was increased 16-, 2.9- and 0.4-fold, respectively. These increases were balanced by a decrease in IgG1 binding which was the most prevalent serum IgG isotype. The results described above suggest that capture techniques are biased and unlikely to provide a coating of IgG isotypes that accurately reflects that of the serum. This bias is derived from the specificity of the individual isotypes for either protein A or protein G, and the errors further compounded by direct competition between isotypes whatever the capture surface. Induced coalescence of IgG3 may explain the latter observations.

Rheumatoid arthritis as a bone marrow disorder

Both the concept of rheumatoid arthritis (RA) as an autoimmune process restricted to joints and the major role of T cells in its pathogenesis have been challenged in the literature. Fibroblastlike and macrophagelike synoviocytes play an important role in RA pannus, and these cells originate in or have their counterpart in bone marrow (BM). Yet the B cell autoimmunity characteristic of RA occurs early, and synovial tissue, like BM, favors the B cell response. Because BM is abnormal in RA, and because germinal centers are unique to RA synovium, RA could be regarded as a disorder of the microenvironments able to sustain B cell response. In fact, RA could even begin in BM, with its onset facilitated by stem cell abnormalities. Moreover, most viruses suspected of playing a role in RA share a BM tropism. This may explain why RA frequently overlaps with other autoimmune disorders and benign lymphoproliferations, such as large granular T lymphocytosis. Because remissions from RA have been reported after BM transplantation, careful studies of the rheumatological outcome of RA patients undergoing such therapeutic procedures are needed. Although RA is a complex process, it can be considered initially as a stem cell disorder requiring treatment similar to that administered to transplant patients. Animal models have provided convincing evidence for these assumptions.

On the interaction between agalactosyl IgG and Fc gamma receptors

One of the serum abnormalities observed in autoimmune diseases such as rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) is the occurrence of IgG that lacks the terminal galactose on asparagine-linked biantennary complex type oligosaccharides [Gal(0)-IgG] located in the CH2 domain. Additionally, IgG without glycosylation is known to be defective in several effector functions due to a reduced ability to bind to its specific receptors (Fc gamma R). It has thus been speculated that, by analogy with unglycosylated IgG, Gal(0)-IgG may also be functionally impaired or exert altered effector mechanisms. If this were true, Gal(0)-IgG could contribute to the phenotype of above-mentioned autoimmune diseases, like impaired immune complex clearance and defective down-regulation of activated B cells. Here, we show by three different methods that the interaction of Gal(0)-IgG and normally glycosylated IgG with the low-affinity Fc gamma RII (CD32) is indistinguishable with respect both to binding and receptor-mediated signalling. These data argue against a prominent role for Fc gamma R-dependent Gal(0)-IgG interactions in the etiology or pathogenesis of autoimmune diseases.

Changes in agalactosyl IgG levels correlate with radiological progression in early rheumatoid arthritis

Immunoglobulin G-lacking galactose (Gal[0]) appears to be helpful in differential diagnosis of early synovitis, and correlates with disease activity in rheumatoid arthritis (RA). Its utility for RA monitoring and prognosis has been evaluated in the present study. Forty-eight patients with early RA were observed for 3 years. Hand radiographs were assessed according to Larsen and results were expressed as damage score (DS) and progression of damage score (PDS). Gal[0], DS, and PDS were evaluated at the onset of the study and after 1 and 3 years. The average values of Gal[0] in RA patients at the onset of the observation were significantly higher as compared to healthy controls (0.43 +/- 0.22 vs. -0.03 +/- 0.09, P < 0.05). The findings of Gal[0] after a 3-year follow-up were also higher as compared to healthy controls (0.37 +/- 0.21 vs. -0.03 +/- 0.09, P < 0.05). Radiological progression (PDS > 15) was observed in 16 patients. This group was characterized by a constantly high level of Gal[0]. The level of Gal[0] in patients without or with moderate radiological progression (PDS < 15) was significantly lower at the onset of the study and remained low during the observation. The relationship between Gal[0] and radiological progression was shown. The data thus far obtained suggest that Gal[0] may serve as an indicator for the disease course in patients with RA. Secondly, we cannot exclude the possibility that the constantly elevated level of Gal[0] causes erosions.

Site-specific glycosylation of human immunoglobulin G is altered in four rheumatoid arthritis patients

Alterations in the glycosylation of human IgG have been shown to occur in rheumatoid arthritis (RA). However, the precise nature and location of these changes have not been fully established. Therefore we carried out a detailed analysis of the oligosaccharides chemically released from intact human serum IgG and fragments of the molecule. Serum samples were from three healthy ('normal') individuals, and from four patients with RA. Site-specific glycolsylation of the glycoprotein was shown to occur, which extended to sites even within the Fab fragment. These were differences in galactosylation, sialylation and the presence of a bisecting N-acetylglucosomide. Disease related alterations were also shown to be site-specific. In particular, an increase in the proportion of agalactosylated oligosaccharides occurred on the Fc fragment in RA (P=0.057), but, in contrast to previous reports there was an increase on the light chain in the proportion of fully galactosylated, bisected and core fucosylated oligosaccharides (from 13% of total in normal to between 18 and 35% in RA, P=0.057)). There was also an Fab-specific increase in oligosaccharides bearing a bisecting N-acetylglucosamine and a core fucose (P=0.075) The site-specific glycosylation changes described in this paper reveal the complexity of the regulatory mechanism, perhaps reflecting the many levels at which regulation can occur.

The Serum Level of Agalactosyl IgG in Rheumatoid Arthritis Patients Treated with Methotrexate

To verify the hypothesis that methotrexate may affect the serum level of agalactosyl IgG (IgG[0]) we followed the changes in IgG galactosylation patterns in a cohort of rheumatoid arthritis patients treated with either methotrexate (MTX) or nonsteroidal antiinflammatory drugs (NSAID).

The average values of IgG[0] in RA patients at the beginning of the observation were significantly higher as compared to healthy controls (0.45 ± 0.39 vs. −0.03 ± 0.09, p<0.05). The findings of IgG[0] after one-year follow-up were also higher as compared to healthy controls (0.38 ± 0.39 vs. −0.03 ± 0.09, p<0.05).

We did not notice any statistically significant difference in IgG[0] between MTX and NSAID treated patients at the beginning of the study (0.49 ± 0.42 vs. 0.42 ± 0.38, NS). However, during one-year MTX treatment IgG[0] significantly dropped (0.49 ± 0.42 vs. 0.25 ± 0.24, p<0.01). We did not establish any fluctuation in IgG[0] in the group of patients treated with NSAID (0.42 ± 0.38 vs. 0.46 ± 0.45, NS).

The data thus far obtained suggest that IgG[0] may serve as an indicator for the disease course in patients with RA. Secondly, the clinical improvement and IgG[0] decrease after methotrexate implies, that the immunoregulatory abnormality in RA may be susceptible to correction by immunotherapy.

Agalactosyl IgG and materno-fetal transmission of autoimmune neonatal lupus

Neither the incidence nor the severity of neonatal autoimmune disease correlates with maternal or neonatal autoantibody titres. However, there is now evidence that the agalactosyl [Gal(0)] fractions of autoantibodies are the most pathogenic. We found that systemic lupus erythematosus (SLE) mothers whose infants developed congenital heart block (CHB) had higher %Gal(0) at the end of pregnancy than did mothers of unaffected infants (P < 0.05) or control mothers (P < 0.01). Similarly, affected infants had higher %Gal(0) than control infants (P < 0.01). Then we studied the Gal(0) content of the anti-Ro and we found that it was higher in affected neonates than in unaffected neonates (P < 0.05), though there was no difference between the corresponding groups of mothers by this criterion. We propose that agalactosyl IgG may have a regulatory or effector role and that the risk of neonates developing maternal autoantibody-mediated disorders may be related to the quantity of agalacotsyl autoantibody present at birth, rather than to its absolute titre.

Short communication: selective placental transport of maternal IgG to the fetus

During pregnancy there is a dramatic reduction in the serum levels of agalactosyl IgG (G0IgG) in both normal women and those with rheumatoid arthritis. In order to determine if a similar reduction in G0IgG were apparent in fetal serum, a comparison of the galactose content of IgG from nine paired samples of umbilical vein or fetal blood and peripheral maternal serum, at gestational ages ranging from 16-41 weeks was performed. The full-term maternal IgG samples were highly galactosylated, so confirming previous observations of reduced G0IgG levels during pregnancy. In addition every paired sample of fetal IgG had a higher level of galactosylation than the corresponding maternal IgG. Therefore, during pregnancy there is both a reduced biosynthesis of the G0IgG glycoform by the mother, and a restriction of its transport across the placenta. The ratio of estimated G0IgG in fetal and maternal serum was found to be related to changes in IgG transport, and in particular the active transport of IgG1 across the placenta during gestation. Our data suggest that the placental IgG transport mechanism is either carbohydrate independent by discriminating for IgG1, or is carbohydrate dependent selecting for highly galactosylated IgG glycoforms. This study emphasizes the need for further investigations on the biological function of G0IgG in normal physiological states, in addition to disease states, such as juvenile and adult rheumatoid arthritis, where elevated G0IgG levels correlate with disease activity.

The glycosylation of red cell autoantibodies affects their functional activity in vitro

Factors governing the functional activity of red cell autoantibodies are poorly defined. Here we report the presence of qualitative differences in the glycosylation of IgG autoantibodies which affect in vitro interactions with Fc gamma RIII. The following antibodies were affinity-purified by adsorption and elution from normal red cells: IgG eluted from the red cells of 27 haemolysing or non-haemolysing patients, anti-D in sera from 11 pregnant women, and IgG1 and IgG3 human monoclonal anti-D. Monoclonal antibodies with differing levels of agalactosyl IgG were produced by culturing cell lines at high or low cell density. The % IgG with oligosaccharides lacking terminal galactose residues (agalactosyl IgG) of antibodies was designated as low, medium or high according to their reactivity with a monoclonal antibody to terminal N-acetylglucosamine. Fc gamma RIII-mediated functional activity was assessed by measuring the K-cell-mediated lysis of red cells in eluates diluted to achieve comparable levels of red cells sensitization. All eluates containing allo-anti-D were lytic (range 74-100%). In contrast, lysis by autoantibodies varied from 0 to 100%; 11/13 eluates from red cells of haemolysing patients promoted > 5% lysis compared to 2/7 eluates from red cells of non-haemolysing patients (P < 0.02). The ability of autoantibodies to promote K-cell-mediated red cell lysis correlated inversely with their level of agalactosyl IgG (r = -0.56, P < 0.01, n = 23). Further, monoclonal anti-D antibodies with very low levels of agalactosyl IgG were comparatively more lytic than the same antibodies containing more agalactosyl IgG. Analysis of the ratio of kappa:lambda light chains suggested that autoantibodies from 6/19 patients were monoclonal or oligoclonal in nature. The data indicate that IgG red cell autoantibodies from different patients are functionally heterogenous, and that this may be due, at least in part, to qualitative differences in the Fc region glycosylation reflected by differences in the proportion of agalactosyl IgG. This heterogeneity is consistent with the clonally-restricted nature of the autoantibodies in some patients.

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

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