Rheumatoid Arthritis IgG Research Articles

Detection of 16α-Hydroxyestrone-histone 1 Adduct as High-Affinity Antigen for Rheumatoid Arthritis Autoantibodies.

Increased concentrations of 16α-hydroxyestrone (16α-OHE1) have been observed in rheumatoid arthritis (RA), but the underlying mechanism of this remains elusive. Here we aimed to identify the role played by 16α-OHE1 in RA. In 40 RA patients, the specificities of antibodies from the sera of these patients were checked by direct binding, inhibition ELISA, and quantitative precipitation titration. Competition ELISA was also used for the estimation of 16α-OHE1 in the serum of different RA patients. RA IgG from a patient's sera showed strong recognition to 16α-OHE1-H1 (histone 1) adduct in comparison to control subjects (p < 0.001), as the formation of this adduct brings out various biochemical changes that might generate neo-epitopes, which have been well-recognized by these antibodies. The affinity of RA antibodies for 16α-OHE1-H1 (1.10 × 10- 7 M) was high, as detected by the Langmuir plot. Comparing RA patients to the controls, no significant differences were detected in the level of 16α-OHE1 or 2-hydroxyestrone/16α-OHE1 ratio. 16α-OHE1-H1 might have an antigenic role and function as a high-affinity antigen for RA autoantibodies and, therefore, could be used as a biomarker for this disease.

Autoantibodies to citrullinated proteins may induce joint pain independent of inflammation

ObjectiveAn interesting and so far unexplained feature of chronic pain in autoimmune disease is the frequent disconnect between pain and inflammation. This is illustrated well in rheumatoid arthritis (RA) where...

Amidase and peptidase activities of polyclonal immunoglobulin G present in the sera of patients with rheumatoid arthritis.

Polyclonal Immunoglobulin (Ig) G from patients with rheumatoid arthritis (RA) and healthy subjects hydrolyzed carbobenzoxy-Val-Gly-Arg p-nitroanilide and D-Pro-Phe-Arg p-nitroanilide. RA IgG exhibited higher activity against the former substrate, but not the latter. On the other hand, RA IgG showed reduced activity against D-Pro-Phe-Arg methylcoumarinamide, when compared with those of the healthy controls. These results suggest that RA IgGs differ from normal IgGs in the substrate specificity of amidase activity. Preliminary studies have shown that two out of three RA IgG samples cleaved a pentapeptide--Gln-Arg-Arg-Ala-Ala--which is assumed to be associated with the risk of developing RA (Gregersen, P. K. et al. (1987), Arthritis Rheum. 30, 1205-1213). By contrast, virtually no cleavage of the same peptide was observed with IgG from healthy controls. A peptide analog, Gln-Arg-Arg-Trp-Ala, was not cleaved at all by any IgGs examined either from RA patients or healthy controls.

Analysis of agalacto-IgG in rheumatoid arthritis using surface plasmon resonance.

It is well established that IgG from rheumatoid arthritis (RA) patients are less galactosylated than IgG from normal individuals. Determination of agalacto-IgG may therefore aid in diagnosis and treatment of RA. The decrease in galactosylation of IgG leads to an increase in terminal N-acetylglucosamine residues, which can be detected using a specific lectin from Psathyrella velutina. In the present study IgG from RA and control serum was purified using affinity chromatography. The samples were then, after reduction, analyzed on a BIOCORE 2000 system with immobilized Psathyrella velutina lectin. Using this technique it was possible to discriminate between IgG from RA patients and IgG from control individuals with respect to its content of IgG with terminal N-acetylglucosamine. The affinity biosensor technique makes it possible to detect binding without labeling or using secondary antibodies.

Human IgG preparations isolated by ion-exchange or protein G affinity chromatography differ in their glycosylation profiles

IgG from patients with rheumatoid arthritis (RA) is abnormally glycosylated in the Fc region, with sialic acid and galactose levels lower than normal. Protein G and DEAE purify populations which are differentially glycosylated. Significantly increased exposure of sialic acid was detected in normal IgG compared with that of RA IgG when ion exchange was used to prepare samples. However, when the same samples were prepared using protein G, no difference in the detection in the detection of sialic acid was seen between the two groups. When examining the heavy chain of IgG, more sialic acid, galactose and N-acetylglucosamine were detected in DEAE purified IgG compared with that prepared by protein G Detection of sialic acid and N-acetylglucosamine was also increased on light chains from IgG prepared by ion exchange chromatography Since this occurs notably on rheumatoid light chains it would appear that this arrangement would contribute to the overall glycosylation changes in IgG. In the case of molecules lacking galactose the discrimination between the RA and normal IgG is significantly improved when ion exchange chromatography is used. Since differentiation between disease and normal groups relies on the purification technique used, we recommend that more than one method is employed before undertaking an analysis of glycosylation changes.

Rheumatoid Factors and Complex Formation

New information regarding rheumatoid factors (RFs) indicates that the RFs synthesized in synovium and lymphoid tissues of patients with rheumatoid arthritis (RA) are different from monoclonal and nonspecific RFs associated with other inflammatory states. The characteristics of RF associated with RA are as follows. They are of all Ig isotypes (not just IgM), indicating T-cell participation in antibody maturation. They have higher avidity for human IgG than for rabbit IgG. They use the human germline heavy-chain variable region (VH) gene VHIII more frequently than other VH genes, and light chains from multiple families. (In contrast, monoclonal RFs use predominantly VH1 and very commonly the V kappa IIIb germline gene HUMkv325). RA IgG is somatically mutated. (In contrast, monoclonal RFs use unmutated germline Ig genes). This suggests they are matured by stimulation either with specific antigens or other activation signals such as cytokines. They are abnormally glycosylated. In general, during periods of disease activity in adult and juvenile RA, a galactose is missing from the Fc of the IgG molecule, leaving an empty "pocket" between the C gamma 2 domains of heavy chains. The IgG RFs self-associate. This may result at least in part when galactose on the F(ab')2 portion of one IgG molecule fills the empty pocket in the Fc of another Ig molecule. Self-association forms immune complexes capable of fixing complement and probably of causing joint damage and vasculitis.

Isolation and analysis of complement activating aggregates from synovial fluid of patients with rheumatoid arthritis using monoclonal anti-C3d antibodies.

The complement activating aggregates in synovial fluids of patients with rheumatoid arthritis (RA) have been isolated using monoclonal IgM anti-C3d antibodies attached to solid phases, and the content of the material bound has been analysed. High levels of aggregated IgG bearing C3d were found in RA synovial fluids, and IgG was the major immunoglobulin bound from such synovial fluids by anti-C3d Sepharose. A strong correlation was shown between levels of aggregated IgG bearing C3d and complement activation, as judged by C3d levels. Significant (but less strong) relationships were also observed between C3d levels and both complement consuming and C1q binding activity. C3d levels and levels of aggregated IgG bearing C3d were both significantly associated with the numbers of polymorphonuclear leucocytes (PMNs) found in RA synovial fluids. From these results it is concluded that the aggregated immunoglobulins bearing C3d (particularly IgG) isolated from RA synovial fluids are responsible for activating complement and attracting PMNs into the joint space. Radioimmunoassay showed no correlation, however, between levels of aggregated IgG (or IgM) bearing C3d and rheumatoid factor (RF) activity bound by anti-C3d. In addition, the material bound by anti-C3d Sepharose from most synovial fluid polyethylene glycol precipitates did not contain either IgM or IgG RF. Thus both techniques show that the majority of complexes bearing C3d do not contain RF. As the complement fixing aggregates apparently contain only immunoglobulin and complement components the results raise the problem of how the aggregates are formed. It is suggested that RA IgG may remain aggregated after either antigen or antibody (RF) has dissociated from the complex.

In vitro studies on the Fc-receptor function of mononuclear phagocytes in rheumatoid arthritis: Relation between the Fc-receptor blockade and the concanavalin A-binding capacity of autologous immunoglobulin G

The Fc-receptor (Fc-R) function of monocytes isolated from 19 control subjects and from 30 patients presenting with a rheumatoid arthritis (RA) was assessed in vitro by a classical rosette assay using IgG-coated sheep red blood cells. In RA patients, the percentage of monocytes forming rosettes was significantly lower than in controls (34.4 +/- 20.4 versus 67.4 +/- 4.5%; P less than 0.001). The blockade observed was reversed by a prior trypsin treatment of RA monocytes, the percentage of recovery being correlated with the IgG plasma levels. Besides, IgG purified from the serum of four RA patients bound a mean of 7.3, 5.2, 1.6, and 1.6 times more than normal IgG did onto concanavalin A (Con A), peanut agglutinin (PNA), phytohemagglutinin (PHA), and pokeweed mitogen (PWM), respectively. Although similar amounts of 125I-labeled normal and RA IgG were bound to normal monocytes, RA IgG inhibited more efficiently than normal IgG the Fc-R function of normal monocytes, for all concentrations tested (10 to 100 micrograms/100 microliters). A prior treatment of RA IgG by alpha-mannosidase, but not by beta-galactosidase, significantly reduced their inhibitory properties. The incubation of monocytes with D-mannose or mannan reduced their capacity to form rosettes. The percentage of monocytes forming rosettes in the presence of both mannan and normal IgG was significantly lower than that measured in the presence of normal IgG only. On the contrary, the rosetting capacity of monocytes in the presence of both RA IgG and mannan was the same as that calculated in the presence of RA IgG only. The inhibitory effect of RA IgG was not related to their abnormal circular dichroism. Our data suggest that the greater ability of RA IgG to block the Fc-R function of monocytes probably depends on the presence of a greater number of accessible mannosyl residues on the glycosidic side chains located in the Fc domain of the molecules.

Investigation of blood platelets in synovial fluid from patients with rheumatoid arthritis.

Synovial fluid (SF) aspirated from inflamed knee joints from each of 13 patients with adult rheumatoid arthritis (RA) was mixed with ACD in the ratio SF/ACD=9:1 with subsequent addition of an equivalent amount of an edta-tris buffer. The mixture was centrifuged to obtain a platelet-rich supernatant. The platelets were washed three times and counted. The same procedure was performed with SF from non-inflamed knee-joints from 3 patients with osteoarthrosis (OA). Direct immunofluorescence (IF) studies were performed with aliquots of platelet suspensions from each SF. In most RA specimens observed under the microscope before separation of platelets, a few small platelet aggregates were observed and platelets were seen in contact with lymphocytes. In all instances, the platelet count appeared to be positively correlated to the total number of white blood cells. In the OA specimens, relatively few platelets were detected, a few lymphocytes were seen in contact with platelets, but no platelet aggregates or correlation between platelets and white blood cell counts were found. Results of the IF studies of RA specimens provide evidence that IgG, IgM and C3 are located on the platelet surface. On the surface of OA platelets, however, only IgG and C3 were detected. Identical staining results were found with washed peripheral platelets from 3 of the RA and 1 of the OA patients. Neither medical treatment nor Waaler serology influenced the staining results. In inflamed SF from RA patients, both IgG aggregates, immune complexes, collagen, and prostaglandins can induce a platelet release reaction with liberation of vasoactive compounds, chemotactic substances and enzymes which can destroy connective tissue, cartilage and bone structures. Interpretations and the significance of the different results are discussed.