Reduced systemic IgG levels against peptidoglycan in rheumatoid arthritis (RA) patients

The gut flora is believed to play a role in the pathogenesis of RA. Peptidoglycan, a major cell wall component of Gram-positive bacteria, is a candidate antigen because of its capability to trigger production of proinflammatory cytokines, to induce arthritis in rodents, and because of its presence in antigen-presenting cells in RA joints. We investigated whether the systemic and local antibody levels against a peptidoglycan-polysaccharide (PG-PS) are related to the presence and disease activity of RA. Significantly lower levels of systemic IgG directed against PG-PS were found in healthy females compared with healthy males, and systemic IgA levels specific for PG-PS were negatively correlated with age. Levels of systemic IgG directed against PG-PS were significantly reduced in RA patients compared with sex- and age-matched healthy controls. Local (synovial fluid) levels of IgG did not correlate with disease activity whereas synovial fluid levels of IgA correlated positively with disease activity. These data suggest that IgG in healthy people mediates protection against spreading of PG to non-mucosal sites.     

Immunoglobulin (Ig)G1 and IgG4 anti‐cyclic citrullinated peptide (CCP) associate with shared epitope,whereas IgG2 anti‐CCP associates with smoking in patients with recent‐onset rheumatoid arthritis (the Swedish TIRA project)

Given the possible importance of anti‐citrullinated peptide/protein antibodies (ACPA) for initiation and progression of rheumatoid arthritis (RA), extended knowledge about the different isotypes and subclasses is important. In the present study, we analysed the immunoglobulin (Ig)G subclasses regarding reactivity against cyclic citrullinated peptides (anti‐CCP) among 504 clinically well‐characterized patients with recent‐onset RA in relation to smoking habits, shared epitope (SE) status and IgA and pan‐IgG anti‐CCP antibodies. All patients, regardless of pan‐IgG anti‐CCP status, were analysed for IgG1–4 CCP reactivity. Sixty‐nine per cent were positive in any IgG anti‐CCP subclass, and of these 67% tested positive regarding IgG1, 35% IgG2, 32% IgG3, and 59% IgG4 anti‐CCP. Among ever‐smokers the percentages of IgG2 anti‐CCP (P = 0·01) and IgA anti‐CCP (P = 0·002)‐positive cases were significantly higher compared to never‐smokers. A positive IgG anti‐CCP subclass ‐negative cases. Combining SE and smoking data revealed that IgG1 and IgG4 anti‐CCP were the IgG anti‐CCP isotypes associated with expression of SE, although the lower number of patients positive for IgG2 or IgG3 anti‐CCP could, however, have influenced the results. High levels of IgG2 anti‐CCP were shown to correlate with expression of the ‘non‐SE’ allele human leucocyte antigen (HLA)‐DRB1*15. In conclusion, in this study we describe different risk factor characteristics across the IgG anti‐CCP subclasses, where IgG2 appears similar to IgA anti‐CCP regarding the predominant association with smoking, while IgG1 and IgG4 related more distinctly to the carriage of SE genes.     

IgG subclasses in collagen-induced arthritis in the rat

Mitogenic lymphocyte stimulation with six concentrations of phytohemagglutinin (PHA) was compared in 60 patients with advanced or metastatic cancer and 30 age- and sex-matched healthy controls using an optimized whole blood method. Since the method is simple and the number of technical variables relatively small, a "normal" range of PHA responsiveness expressed in absolute cpm, could be established. It is thus possible to directly compare results from different laboratories. A markedly reduced lymphocyte stimulation was found in cancer patients compared to controls, although leukocyte and lymphocyte counts were almost "normal". The implications of this finding are discussed with regard to immunosuppression by the tumor and previous chemotherapy.     

Glycosylation of IgG, immune complexes and IgG subclasses in the MRL-lpr/lpr mouse model of rheumatoid arthritis

The MRL-lpr/lpr (MRL/lpr) mouse spontaneously develops a disease syndrome which, in many respects, is similar to human rheumatoid arthritis. These mice developed joint inflammation, circulating rheumatoid factors and immune complexes. We now show that the parallel with human disease extends to a glycosylation defect which is observed on IgG from rheumatoid arthritis patients. Using the lectins ricin and Bandeiraea simplicifolia II we have found that terminal N-acetylglucosamine is clearly raised in MRL/lpr IgG. Increased exposure of galactose was also detected, indicating that a second glycosylation site must be present on these molecules. Polyethylene glycol-precipitated IgG complexes bound significantly more of each lectin than did free IgG, indicating that the changes in glycosylation were associated with complex formation. The sugar abnormality was most marked in the IgG2a/IgG3 fraction from protein A IgG subclass chromatography. Our results suggest that the IgG glycosylation defect seen in rheumatoid arthritis is apparent in the MRL/lpr mouse and may contribute, through complex formation, to the pathological processes in the rheumatoid syndrome.     

Autoantibodies to citrullinated antigens in (early) rheumatoid arthritis

Rheumatoid arthritis (RA) is a common, systemic autoimmune disease characterized by chronic inflammation of the synovium, that can lead to progressive joint destruction and in many cases results in severe disability and poor quality of life. With the availability of more sophisticated and effective therapies and with increasing evidence that the first few months of disease represent an unique therapeutic opportunity and that such early therapeutic intervention is crucial in preventing irreversible joint damage, it is widely accepted that early and accurate diagnosis of RA is critical in disease management. Within the last three years a growing number of publications have reported that the second generation anti-CCP (cyclic citrullinated peptide) test may become the marker of choice for diagnosing early RA as it appears to be highly specific for the disease with a sensitivity comparable to the widely used but less specific rheumatoid factor test. Additionally, anti-CCP2 positivity can predict future development of RA in both asymptomatic individuals and in patients with undifferentiated arthritis. Furthermore, antibody levels at presentation can correlate with progression to erosive disease.     

Genetic risk factors for infection in patients with early rheumatoid arthritis

We analyzed clinical and genetic factors contributing to infections in 457 subjects with early rheumatoid arthritis (RA) enrolled in a prospective, 1-year clinical trial of methotrexate and the TNF inhibitor etanercept. Subjects were genotyped for the following single nucleotide polymorphisms (SNPs): (TNF -308, -238, and + 488); lymphotoxin-alpha (LTA) (LTA + 249, + 365, and + 720); and Fc gamma receptors FCGR2A 131 H/R; FCGR3A 176 F/V; and FCGR3B NA 1/2 and genotypes were correlated with infections. At least one URI was noted in 52% of subjects (99/191) with the NA2/NA2 genotype of the neutrophil-specific FCGR3B gene, compared to 42% (77/181) of those with the NA1/NA2 genotype and 39% (23/59) of those with the NA1/NA1 genotype (P = 0.038). Urinary tract infection (UTI) was associated with the TNF -238 A (odds ratio(OR) 2.56, 95% confidence interval (CI) 1.05-6.25) and LTA +365 C (OR 1.73, 95% CI 1.07-2.79) alleles, and marginally with the FCGR3A F allele (OR 1.72, 95% CI 0.99-3.00). There was a striking linear correlation between UTI and the number of risk alleles defined by these three SNPs (P < 0.001), suggesting an additive effect on susceptibility. These findings have important implications for the role of genetics in susceptibility to bacterial and viral infections.     

IgG subclasses in human immune response to wild and attenuated (vaccine) Junin virus infection

Different proportions of IgG subclasses have previously been reported to distinguish the immune response elicited by primary and recurrent viral infections, as well as viral vaccines. The goal of this study was to study the IgG subclasses composition in the immune response of patients with Argentine hemorrhagic fever, and vaccinees with Candid #1 strain of Junin virus. Twenty-four individuals inoculated with Candid #1 vaccine and 67 patients with Argentine hemorrhagic fever were studied. Blood samples were drawn at 30, 60, and/or 180 days post-inoculation with Candid #1 and 30, 60, and 90 days after clinical onset of the disease. Specific anti-Junin virus IgG subclasses were titrated with specific human monoclonal antibody fluorescence isothiocyanate conjugate (FITC) by immunofluorescent assay (IFA). IgG(1) anti-Junin virus was found in every subject studied and IgG(3) was also detected in some patients with a severe form of Argentine hemorrhagic fever. IgG(2) and IgG(4) were not detected in any serum sample studied. The mean titer of specific IgG(1) in vaccinees was significantly lower than in patients with Argentine hemorrhagic fever (P < 0.05), but no difference was found between mild and severe cases of the disease (P > 0.05). The results of this study demonstrated a central role of IgG(1) in human recovery from infection with every strain of Junin virus, an observation stressed by the immune response to Candid #1 vaccine, which resulted in no difference in IgG subclasses composition from that found in mild cases of Argentine hemorrhagic fever.     

Immunological properties of isolated IgG and IgM anti-gamma-globulins (rheumatoid factors)

Anti-gamma-globulins of the IgG and IgM classes have been isolated from sera of normal individuals and from patients with osteoarthritis, rheumatoid arthritis and juvenile rheumatoid arthritis. All of the isolated antibodies gave precipitin curves with heat-aggregated, reduced and alkylated gamma-globulin. IgM anti-gamma-globulins gave a positive latex fixation test at 4°C and 37°C while IgG anti-gamma-globulins generally gave a positive test only at 4°C. Anti-gamma-globulins from normals did not fix complement but IgG and IgM anti-gamma-globulins from rheumatoids fixed complement to a similar degree. This in vitro complement fixation could account at least in part for the diminished complement levels seen in many rheumatoid synovial effusions.     

抗环瓜氨酸肽抗体对类风湿关节炎的极早期预测

类风湿关节炎(RA)的早期治疗(指疾病发作的前两年内)能减轻炎症的活动性.而发病的前几个月治疗在质量上明显优于后期治疗.但问题是如何能把要发展成RA的滑膜炎病人与不会发展成RA的病人区分开来[1,2].最近发现,抗环瓜氨酸肽(CCP)抗体出现先于RA.     

The influence of early life factors on the risk of developing rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disease that develops as a result of the interaction between genetic and environmental risk factors. Although increasing evidence shows the importance of genes in determining the risk of RA, it is clear that environmental factors also have a vital role. Studies to date have tended to concentrate on environmental influences around the time of disease onset. However, a number of pieces of evidence, including the fact that autoantibodies, such as rheumatoid factor (RF), can develop several years before the onset of clinical disease, suggest that environmental factors may influence disease susceptibility during early life. Several recent studies lend weight to this possibility, with an increased risk of RA in the offspring of mothers who smoked during pregnancy and in those with higher birth weight. There has also been a suggestion that the risk of RA is reduced in breast-fed infants. We describe the evidence surrounding the effect of early life factors on the risk of developing RA and possible mechanisms by which they may act.     

The role of IgG glycoforms in the pathogenesis of rheumatoid arthritis

Conclusions In conclusion, there is a shift in the population of IgG glycoforms towards those with a higher content of agalactosyl biantennary N-linked oligosaccharides in active rheumatoid arthritis (both juvenile and adult), tuberculosis, and Crohn's disease, but not in a variety of other rheumatological, inflammatory, or infectious conditions. This shift may contribute to disease pathogenesis both through immune-complex formation and through disturbance of a cellular network directed against the non-reducing terminal G1cNAc epitope. The precise pathology would in each case be modulated by the anatomical site(s) of production of such IgG, and also by the precise mechanism inducing this change in IgG glycosylation. Important amongst such mechanisms may be cross-reactivity between environmental and endogenous carbohydrate epitopes. It will be interesting to see if future research supports the idea that groups of diseases (e. g., rheumatoid arthritis, tuberculosis, Crohn's) are indeed related by a common aetiopathogenesis [i. e., G(0)].     

Humoral autoreactivity directed against surfactant protein-A (SP-A) in rheumatoid arthritis synovial fluids

SP-A is found principally in the lung, and has been associated with lamellar bodies also found in the synovial joint. Both SP-A and C1q contain collagen-like regions, and SP-A and C1q have some structural similarities, both having a globular head region and a collagen-like tail. Here we are able to show that (i) autoreactivity to SP-A, as expressed by IgG and IgM autoantibodies, is present in synovial fluid (SF) isolated from patients with rheumatoid arthritis (RA); (ii) in absorption experiments only a limited degree of cross-reactivity between autoantibodies reactive with C1q and SP-A is observed; (iii) there is no cross-reactivity between autoantibodies reactive with type II collagen (CII) and those reactive with SP-A or C1q; (iv) autoantibodies react with polymeric (dimers and larger) SP-A, but not with monomeric SP-A subunits, indicating that a degree of quaternary structure is required for antibody binding. Unlike CII, which not accessible in the normal joint, both SP-A and C1q are available within the SF in patients with RA and may therefore provide antigens driving an autoimmune response directed against collagen-like structures.     

Rituximab impairs immunoglobulin (Ig)M and IgG (subclass) responses after influenza vaccination in rheumatoid arthritis patients

Rituximab (RTX) treatment in rheumatoid arthritis (RA) patients severely hampers humoral response after influenza vaccination as determined by haemagglutination inhibition assay (HI). It is not known whether HI reflects both immunoglobulin (Ig)M and IgG (subclass) influenza response, and whether IgM antibodies contribute to the low rate of influenza infection seen in RA patients. Twenty RA patients on methotrexate (MTX), 23 on RTX and 28 healthy controls (HC) received trivalent influenza subunit vaccination. Before and 28 days after vaccination, H1N1‐ and H3N2‐specific antibodies were measured by HI and by IgM and IgG (subclass) enzyme‐linked immunosorbent assay (ELISA). B cell activating factor (BAFF) levels were determined in serum samples before vaccination. Vaccination induced a significant increase of IgM and IgG (IgG1 and IgG3) antibodies against both strains in the HC and MTX groups (all P < 0·01), but not in the RTX group. HI correlated significantly in all cases with IgG (IgG1) but not with IgM. In RTX late patients (RTX treatment 6–10 months before vaccination), IgG (IgG1 and IgG3) response to vaccination was restored, but not IgM response. BAFF levels were significantly increased in RA‐RTX patients and correlated with total IgG levels. Haemagglutination inhibition assay, used as gold standard, detects primarily IgG (IgG1) responses. IgM‐ and IgG influenza‐specific antibodies increase after vaccination in HC and RA patients except in patients on RTX treatment. BAFF levels are increased in both early and late RTX‐treated patients, but do not correlate with an influenza‐specific antibody response.     

Anti-CCP antibodies, a highly specific marker for (early) rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic, destructive autoimmune disease affecting the joints. With more sophisticated and effective therapies becoming available and with the understanding that early intervention is crucial in preventing irreversible joint damage, it is more and more important to diagnose RA at a very early stage in the disease. To facilitate diagnosis during the early stages of the disease, when often not all clinical symptoms are manifest, a good serological marker is needed. Antibodies directed to citrullinated proteins provide this ability. The most sensitive assay to detect these antibodies is the so-called anti-cyclic citrullinated peptide (CCP) enzyme-linked immunosorbent assay (ELISA) assay. In this review, the diagnostic and prognostic potential and the general utility in clinical practice of anti-CCP antibodies are discussed. Furthermore, we elaborate on the mechanisms involved in the generation of citrullinated autoantigens and the possible role of the anti-CCP antibodies and their antigens in the disease.     

False-positive signals in enzyme immunoassay (EIA) interactions between rodent IgG subclasses

Interactions between mouse and rat monoclonal antibodies (MAbs) in EIA have been detected using panels of mouse and rat MAbs of various isotypes. Mouse and rat antibodies of the IgG2a subclass were found to bind to each other most strongly. Immobilised IgG1 antibodies of the two species showed much less interaction. Rat IgG2b and IgG2c were intermediate in binding activity. We were unable to study examples of mouse IgG2b and IgG3 MAbs. By making use of the kappa light chain allotype in the rat we were also able to show intraspecies interactions of rat MAbs with the IgG in rat serum. The molecular basis of these interactions has not been resolved but may involve the extended hinge region and flexible Fab arms of the IgG2a subclass of Ig permitting strong inter domain bonding between the constant region domains of adjacent molecules of this isotype.     

Alloimmunization to human immunoglobulin genetic markers is frequent in early rheumatoid arthritis.

HLA and Gm allotypes of 99 consecutive Swedish patients with rheumatoid arthritis were determined. Ninety-two of the 198 haplotypes contained DR4, a significant increase. The patients' sera from 3 different occasions were studied for anti-immunoglobulin profile as judged by 6 selected anti-Rh coats, 4 of them being monoclonal anti-Ds restricted as to allotype. Ninety-two of the patients were reactive with a polyclonal anti-Rh Ri as against 10 with the monoclonal carrying the G1m(f) allotype. Antibodies to Ig coats carrying defined allotypes were more frequently observed in patients not carrying the allotype in question than in those individuals possessing it. The difference was significant or highly significant as regards presence/absence of G1m(a), G3m(b) and G3m(g), respectively. Anti-G1m(a) and anti-G3m(g) cooccurred in 17 of the patients. Results consistent with presence/absence of particular anti-immunoglobulins at the 3 examinations were observed in 74 of the patients. Gm allotypes or antiallotypes were not statistically related with DR4 status. In conclusion, alloimmunization to Gm markers frequently occurs in early rheumatoid arthritis.     

IgG subclass-specific antibodies to human cytomegalovirus (HCMV)-induced early antigens

We investigated the IgG subclass reactivity pattern to early antigens (EA) of human cytomegalovirus (HCMV) in 217 EA-antibody-positive sera from immunocompetent, healthy persons, renal transplant recipients and AIDS patients by immunoblotting. All IgG subclasses are involved in the IgG immune response to HCMV EA. IgG 1 was the major subclass reacting with HCMV EA (with a molecular mass ranging between 23- and 79-kDa) and was present in all sera irrespective of origin. Antibody responses of IgG isotypes 2, 3 and 4 were observed with lower frequency and reactivity, whereas IgG3 was detectable more frequently and reacted slightly stronger than IgG2 and 4. The IgG1 reactivity pattern was similar to that seen with total IgG. In contrast to total IgG and IgG 1, the reactivity of the sub-classes 2, 3 and 4 was not equally distributed among the early polypeptides, but was mainly directed to some of them (79-, 70-, 66-, 43- and 38-kDa). On average primary infections seem to induce a stronger IgG3 response to the 79-, 70- and 38-kDa proteins than reactivated infections and an increased IgG 1 to the 79-, 70-, 59-, 56- and 50-kDa proteins appeared to be associated with severe disease. Noteworthy was the significantly lower prevalence of IgG 1 antibodies to the 70-kDa protein in human immunodeficiency virus (HIV)infected individuals when compared to renal transplant recipients and immunocompetent, healthy individuals. Since the IgG 1 immune reaction to this protein occurred five to seven times more frequently in healthy persons and renal transplant recipients, the decreased formation of IgG 1 antibodies to the 70-kDa protein might be a characteristic feature of HIV infection.     

An autoantibody targeting glycated IgG is associated with elevated serum immune complexes in rheumatoid arthritis (RA)

Advanced glycation end-products (AGE) play a role in diabetes complications and in RA. An autoantibody to IgG-AGE has been shown to correlate with RA disease activity. Thus we sought to analyse serum immune complexes (IC) and AGE-modified proteins in Caucasians and North American Indians to see if the presence of anti-IgG-AGE influenced their composition. Polyethylene glycol precipitation of IC from the serum of anti-IgG-AGE-positive or -negative RA patients, and healthy and diabetic controls were examined. Concentrations of circulating IC were highest in anti-IgG-AGE+ RA patients, followed by anti-IgG-AGE- RA patients, which were greater than healthy controls. IC amounts in the Ojibwe were consistently higher than in Caucasians. Affinity purification of AGE-modified proteins from IC and immunoblotting with antibodies against Ig gamma and mu heavy chains, kappa and lambda light chains, and AGE Nepsilon(carboxymethyl)lysine and imidazolone yielded similar results: anti-AGE+ RA patients had elevated levels relative to those without the autoantibody. Levels in both RA groups were higher than in controls. Glycated albumin amounts followed a similar distribution, but were not influenced by the presence of anti-AGE antibodies. A heavily glycated kappa-chain was present primarily in IC from anti-IgG-AGE+ patients. These studies indicate that anti-AGE antibodies have a direct impact on the accumulation of IgG-AGE but not glycated albumin, and may block the normal clearance of IgG-AGE through AGE receptors.     

Subclass distribution of IgG antibodies to the rat oesophagus stratum corneum (so-called anti-keratin antibodies) in rheumatoid arthritis.

Serum IgG, labelling the stratum corneum of the rat oesophagus epithelium, so-called anti-keratin antibodies (AKA) constitute the most specific marker for the diagnosis of rheumatoid arthritis. In this study, we investigated 31 IgG AKA-positive rheumatoid sera and 21 control sera from patients with non-rheumatoid inflammatory rheumatic diseases. The serum level of IgG1,2,3 and 4 was determined by radial immunodiffusion and the subclass distribution of IgG AKA by a three-step semi-quantitative immunofluorescence assay using standard monoclonal antibodies specific for each of the four human IgG subclasses. In the rheumatoid sera, the serum level of IgG1 was found to be significantly increased and the level of IgG2 significantly decreased with regard to the control sera, while the levels of IgG3 and 4 as well as total IgG were in the normal range. IgG1,2,3, and 4 AKA were detected in 27 (87%), 6 (19%), 4 (13%) and 11 (35%) of the 31 rheumatoid sera, respectively, and were found to be independent of the clinical and biological indices of the disease. In spite of inter-individual heterogeneity, two predominant profiles were distinguished: IgG1 (alone) and IgG(1 + 4), which together represented 18 sera (58%). The large predominance of IgG1 AKA and the quasi-absence of IgG2 AKA suggest that the recognized antigen may be partly comprised of protein. Moreover, the high frequency of occurrence of IgG4 AKA might result from chronic exposure to the eliciting antigen, which could be a genuine autoantigen since we demonstrated that it is also present in the stratum corneum of human epidermis.