Increased C1q binding immune complexes in Felty's syndrome: comparison with uncomplicated rheumatoid arthritis

Inflammatory properties of IgG modified by oxygen radicals and peroxynitrite

In inflammatory arthritis, there is evidence indicating that the affected tissues produce large amounts of oxygen-free radicals and NO. Herein, we examine the biologic effects of exposure of IgG to hypochlorous acid (HOCl) and peroxynitrite (ONOO). The concentrations of IgG modified by chlorination and nitrosation were measured in synovial fluids from inflammatory and noninflammatory arthritis. Human IgG was exposed to increasing concentrations of HOCl and ONOO, and the resulting products were tested for complement component binding; binding to FcgammaRI; activation of polymorphonuclear neutrophils; effect on the Ab-combining site of Abs; and in vivo inflammatory activity in a rabbit model of acute arthritis. Rheumatoid synovial fluids contained significantly greater concentrations of nitrosated and chlorinated IgG compared with ostearthritic specimens. In vitro exposure of human IgG to HOCl and ONOO resulted in a concentration-dependent decrease in C3 and C1q fixation. The decrease in Fc domain-dependent biologic functions was confirmed by competitive binding studies to the FcgammaRI of U937 cells. HOCl-treated IgG monomer was 10 times less effective in competing for binding compared with native IgG, and ONOO-treated IgG was 2.5 times less effective. The modified IgGs were also ineffective in inducing synthesis of H(2)O(2) by human PMN. The Ag-binding domains of IgG also showed a concentration-dependent decrease in binding to Ag. The ability of the modified IgGs to induce acute inflammation in rabbit knees decreased 20-fold as gauged by the intensity of the inflammatory cell exudates. These studies clarify the modulating role of biological oxidants in inflammatory processes in which Ag-autoantibody reactions and immune complex pathogenesis may play an important role.

Effect of circulating immune complexes on the binding of rheumatoid factor to histones

OBJECTIVE

To determine whether the reaction of rheumatoid factor (RF) with solid phase histone is due to the simultaneous presence of circulating immune complexes (CICs) or aggregated IgG.

METHODS

Serum samples from 56 patients with seropositive rheumatoid arthritis (RA) and 50 random blood bank donors were used. Binding of immunoglobulins to histone was determined by enzyme linked immunosorbent assay (ELISA) and by western blots. Aggregated IgG was obtained by heating at 61(o)C for 30 minutes.

RESULTS

Among the RA sera tested by ELISA, 54% were positive for histone binding by IgM, IgG, or IgA and 20% by IgM only. Heating of normal sera caused a significant enhancement in the binding of IgG to histone (p<0.001). This binding had a non-cognate behaviour-that is, it was destroyed by pepsin treatment of serum and was not significantly inhibited by competition with free histone. The same behaviour was seen for IgM, IgG, and IgA binding from RA sera. However, cognate IgG antibody binding to histone was inhibited by free histone and was resistant to pepsin digestion. Addition of heat aggregated IgG to RA sera or pretreatment of histone with aggregated IgG caused a significant increase in IgM binding to histone.

CONCLUSION

IgM, IgG, and IgA RF bind to solid phase histone as a result of attachment to histone of immune complexes or aggregated IgG and not as a result of a cognate reaction with histone.

Reversal of neutropenia with methotrexate treatment in patients with Felty's syndrome. Correlation of response with neutrophil-reactive IgG

We evaluated the clinical and hematologic response to methotrexate (MTX) in 4 women with Felty's syndrome (FS) who had had neutropenia for 1-3 years. Since immune complexes or antineutrophil antibodies are implicated in the pathogenesis of the neutropenia of FS, we also measured both direct and indirect levels of neutrophil-reactive IgG. All 4 patients showed a prompt and dramatic increase in neutrophil counts within 1-2 months of starting MTX therapy. In 3 patients, the symptoms of arthritis also improved; in the fourth patient, arthritis worsened. Recurring infections ceased in 3 patients. Neutrophil-reactive IgG levels, which were elevated in all patients prior to treatment, decreased toward normal while the patients were receiving MTX therapy. We conclude that MTX is effective in treating the neutropenia of FS, in part by lowering neutrophil-reactive IgG.

Immune complexes and the pathogenesis of neutropenia in Felty's syndrome

The effect of the injection of serum from patients with rheumatoid arthritis (RA) and Felty's syndrome (FS) into mice on the number of circulating polymorphonuclear cells (PMN) was studied. The number of circulating PMN dropped to 61% (range 34-98%) of the initial counts after the injection of FS serum. This phenomenon was observed less frequently after injection of RA serum. In contrast, injection of serum from healthy controls always resulted in an immediate increase in the number of circulating PMN. No decrease in PMN counts was found after injection of FS sera pretreated with polyethylene glycol to precipitate immune complexes (IC). Gel filtration of FS sera on Sepharose 4B showed that the effect on the PMN counts in mice did not coincide with the 7S peak but occurred only in fractions containing larger material. Serum fractions from FS patients that contained IC were more active in producing neutropenia than the corresponding fractions from patients with RA. Microscopic and immunohistochemical examination of the organs from mice injected with FS serum showed sequestration of PMN and deposition of human IgG, IgA, and IgM in the vascular bed of the lungs. These results indicate that the interaction between PMN and IC of patients with FS leads to sequestration of PMN in mice and suggests that this interaction in humans may have a role in the pathogenesis of FS.

Antinuclear antibody determination: the present state of diagnostic and clinical relevance

Determination of antinuclear antibodies (ANA) will gain in diagnostic significance if a specific type of ANA can be related to a defined clinical disorder. The past decade has brought us quite a lot of papers dedicated to this subject. Yet, with exception of the DNA/anti-DNA system, observed correlations have remained scarce or contradictory. Also, still little is known about the pathogenic role of ANA. Perhaps more recent approaches using biochemical technologies will provide us with highly purified nuclear antigens necessary to study possible correlations at a more sophisticated level.

Felty syndrome: autoimmune neutropenia or immune-complex-mediated disease?

Immunofluorescence on polymorphonuclear cells (PMN) of patients with Felty syndrome (FS) revealed increased amounts of IgG, IgA, and IgM bound to the PMN surface compared with PMN of patients with rheumatoid arthritis alone. A positive correlation was found between the score for surface-bound immunoglobulins on FS-PMN and the results of the Clq binding assay in FS sera. After preincubation with sera from 20 patients with FS, immunofluorescence on PMN from healthy controls (HC) showed that these cells had bound IgG, IgA, and IgM. However F(ab')2 fragments of IgG from FS sera did not bind to PMN, although the antigen-binding reactivity of the F(ab')2 fragments was maintained as shown by control experiments. Immunoglobulins eluted from FS-PMN failed to bind to HC-PMN, whereas the corresponding IgG of patients with autoimmune neutropenia was bound. Gel filtration of FS sera on Sepharose 4B showed that the binding of IgG in FS sera to PMN did not coincide with the 7S peak but occurred mainly in fractions containing larger material. No binding of IgA and IgM to HC-PMN was found after incubation with FS sera pretreated with polyethylene glycol (PEG) to precipitate immune complexes. These results indicate that in sera of patients with FS the PMN-binding reactivity of IgG, IgA, and IgM is due to the binding of immune complexes containing these immunoglobulins and not to presence of autoantibodies directed to antigens on the neutrophil surface.

IgE class immune complexes in Felty's syndrome: characterisation of antibody activities in isolated complexes

By means of a double polyethylene glycol (PEG) precipitation and PRIST technique IgE was detected in 3% PEG precipitates and in the immune complex enriched fractions purified by solid-phase Clq adsorption from sera of 11 of 20 patients with Felty's syndrome. No correlation was found between the occurrence of complexed IgE and total protein content of the immune complex enriched material. IgE rheumatoid factor and anti-IgE antibody activity were detected in some of the immune complex fractions. Serum levels of complement C3, C4, and factor B were low in IgE immune complex positive cases. Only 4 of 20 patients with articular rheumatoid arthritis had IgE-containing immune complexes.

Lack of activation of C1, despite circulating immune complexes detected by two C1q methods, in patients with rheumatoid arthritis

The activation of C1 by circulating immune complexes in patients with rheumatoid arthritis was investigated. C1rC1s(C1-In)2 complexes in EDTA-plasma, reflecting C1 activation in vivo, were slightly raised in 35 of 57 patients with rheumatoid arthritis, though most patients had elevated levels of circulating immune complexes as measured with either the 125I-C1q binding test or the C1q solid phase assay. The activation of C1 by circulating immune complexes in vitro was investigated by measuring the generation of C1rC1s(C1-In)2 complexes during 60 minutes at 37 degrees C in diluted recalcified EDTA-plasma. In 16 of the 57 patients, a slightly increased C1 activation in vitro was observed. These patients tended to have high levels of circulating immune complexes. However, the majority of the patients with high levels of circulating immune complexes showed a normal C1 activation in vitro. Therefore, it was concluded that measurement of circulating immune complexes by either of the two C1q methods in patients with rheumatoid arthritis does not imply that these circulating immune complexes are able to activate C1.

Anti-Fab' antibodies in rheumatoid arthritis. Measurement of the relative quantities incorporated in soluble immune complexes in sera and supernatants from cultured peripheral blood lymphocytes

High levels of anti-immunoglobulins that react with Fab' fragments of IgG have been observed in sera of patients with rheumatoid arthritis (RA). To determine how much of these anti-Fab' antibodies are incorporated within immune complexes (IC), we added 125I-Fab' to sera and then measured the amount of labeled Fab' that could be precipitated by adding polyethylene glycol (PEG). Sera were either maintained at neutral pH during this procedure or acidified (pH 3) to dissociate IC. Acidification permitted the 125I-Fab' an equal chance to compete with other endogenous antigens for anti-Fab' antibodies, once excess hydrogen ion was removed. Quantities of anti-Fab' in sera of 20 seropositive RA patients were greater than in sera of 43 age- and sex-matched healthy controls, as measured by this assay and by a solid phase radioimmunoassay. However, significantly less anti-Fab' antibody was incorporated in ICs in the RA patients' sera. Supernatants from cultured peripheral blood lymphocytes of RA patients also contained relatively more "free" and less "hidden" anti-Fab' than culture supernatants from controls. Thus there appear to be qualitative as well as quantitative differences in the anti-Fab' antibodies synthesized by RA patients. This may reflect different proportions of IgM and IgG anti-Fab' in their sera, differences in the average avidity of these antibodies, or differences in the reciprocal relationships within the idiotypic network that result in release of antibodies by certain antibody-producing cells, but not by clones that produce complementary idiotypes.

Heterogeneity of bone marrow-directed immune mechanisms in the pathogenesis of neutropenia of Felty's syndrome

Twenty-seven patients with Felty's syndrome were studied by the colony forming unit in culture (CFU-C) assay for possible immune mechanisms within the bone marrow compartment that could contribute to the neutropenia. Depletion of bone marrow suppressor T cells resulted in normal CFU-C numbers in 7 patients. In 5 patients serum antiprecursor cell activity was detected. Blood monocytes failed to generate colony stimulating factor in 5 patients. Bone marrow-directed immune mechanisms are heterogeneous and could play a role in the pathogenesis of neutropenia in some patients with Felty's syndrome.

Critical aspects of immune complex assays employing polyethylene glycol

Treatment of artificial immune complexes (ICs) with 2.5% polyethylene glycol (PEG)--conditions under which C1q-binding activity is routinely measured in the fluid phase--produced marked changes in molecular size as determined by Sepharose 6B chromatography. The effect of PEG on the C1q-binding capacity of ICs, was therefore investigated using a solid phase (SP) system. PEG enhanced the binding of aggregated human gammaglobulin (AHG) and artificial ICs to SP-C1q and, in reverse experiments, also increased the binding of C1q to SP-AHG. The degree of enhancement varied according to the Ag:Ab ratio employed; the binding of ICs formed in moderate Ab excess was only modestly enhanced but that of complexes formed at slight Ab excess, equivalence and Ag excess was markedly elevated. The profile of PEG-induced enhancement of binding paralleled that of similar ICs in the C1q fluid phase system, suggesting that C1q binding in the latter may be influenced by PEG. However, the C1q-binding activity of in vivo-formed ICs seemed to be relatively unaffected by PEG since enhanced binding was comparable in control and pathological sera. The results indicate that PEG causes cross-linking and aggregation of ICs (and possibly other serum proteins) which may alter their biological activity and hence influence the results of IC assays that employ this agent.

High serum beta-2-microglobulin levels and circulating immune complexes containing beta 2m and anti-beta 2m antibodies in Felty's syndrome

Serum beta-2-microglobulin (beta 2m) levels, incidence and levels of anti-beta 2m autoantibodies, and quantity of circulating macromolecular complexes containing beta 2m were studied in patients with Felty's syndrome (FS), joint-restricted rheumatoid arthritis (RA), and healthy controls. The serum beta 2m concentrations detected in the FS group (6.95 +/- 2.9 mg/liter) greatly exceeded those of the RA group (3.4 +/- 1.2 mg/liter) and the control group (1.42 +/- 0.69 mg/liter). Autoantibodies to beta 2m were frequent in the FS group. Circulating complexes containing beta 2m, prepared by precipitation in 3% polyethylene glycol, were detected in 65% of FS and 35% of RA patients. In the majority of these cases the solid-phase C1q purified immune complexes also contained beta 2m. Detection of anti-beta 2m antibodies in a significant part of complexes containing beta 2m suggests the presence of specific immune complexes in this fraction of FS and RA patients.

Activation of human complement by immunoglobulin G antigranulocyte antibody

The ability of antigranulocyte antibody to fix the third component of complement (C3) to the granulocyte surface was investigated by an assay that quantitates the binding of monoclonal anti-C3 antibody to paraformaldehyde-fixed cells preincubated with Felty's syndrome serum in the presence of human complement. The sera from 7 of 13 patients with Felty's syndrome bound two to three times as much C3 to granulocytes as sera from patients with uncomplicated rheumatoid arthritis. The complement-activating ability of Felty's syndrome serum seemed to reside in the monomeric IgG-containing serum fraction. For those sera capable of activating complement, the amount of C3 fixed to granulocytes was proportional to the amount of granulocyte-binding IgG present in the serum. Thus, complement fixation appeared to be a consequence of the binding of antigranulocyte antibody to the cell surface. These studies suggest a role for complement-mediated injury in the pathophysiology of immune granulocytopenia, as has been demonstrated for immune hemolytic anemia and immune thrombocytopenia.

Comparison of five assays for immune complexes in the rheumatic diseases. An assessment of their validity for rheumatoid arthritis

Clinical assessment (disease activity, severity, and extraarticular manifestations) of 101 rheumatoid arthritis patients was correlated with several laboratory tests, including 5 immune complex assays: the bovine conglutinin, 125I-Clq binding, monoclonal rheumatoid factor inhibition, Raji cell, and staphylococci binding assays. Elevated disease activity indices were most closely associated with the presence of immune complexes detected by the 125I-Clq and staphylococci binding assays. There were significant but weak correlations between the level of disease activity and the level of immune complexes as measured by the bovine conglutinin, 125I-Clq binding, Raji cell, and staphylococci binding assays. Articular disease severity, as measured by anatomic stage, was discriminated by the bovine conglutinin, monoclonal rheumatoid factor inhibition, and staphylococci binding assays. Extraarticular manifestations were best discriminated by the Raji cell and staphylococci binding assays. We concluded that the sensitivity, specificity, predictive value, and overlap of the associations were not sufficient to warrant their wide use for the diagnosis and management of rheumatoid arthritis in individual patients. Conversely, the 125I-Clq and staphylococci binding assays were as good as the erythrocyte sedimentation rate and the IgG rheumatoid factor test (the 2 best of many examined) in assessing disease activity. Further prospective studies with these assays will determine their usefulness in following rheumatoid arthritis for a prolonged period.

Neutropenia in rheumatoid arthritis: studies on possible contributing factors

Twenty-five patients with rheumatoid arthritis (RA) and neutropenia, of whom 19 had a palpable spleen, were compared with 24 patients with uncomplicated RA, and 16 patients with RA and associated splenomegaly without neutropenia. Clinically patients with neutropenia had evidence of a more systemic disease as assessed by prevalence of rheumatoid nodules, weight loss, and recurrent infections. However, there was less evidence of active synovitis than in the other 2 groups. Marrow neutrophil reserve was studied by means of a hydrocortisone stimulation test and was found to be lower in all 3 groups than in normal persons but with most marked depletion in the neutropenic group. Removal of the spleen in some patients with neutropenia resulted in a significant increase in marrow neutrophil reserve. Circulating immune complexes as detected by anticomplementary activity and platelet aggregation tests were detected in 68% of the RA neutropenia group, 31% of the RA splenomegaly group, and 8% of the uncomplicated RA group. Our results show that, assessed both clinically and by the above tests, patients with neutropenia have a greater prevalence of abnormalities which may be directly related to their neutropenia. Patients with splenomegaly alone closely resemble patients with uncomplicated RA.

Human neutrophil swelling induced by immune complexes and aggregated IgG

Using a Coulter counter method, the effects of various types of IgG-dependent phagocytic stimuli on human neutrophil (PMN) swelling were determined. Human heat aggregated IgG, ovalbumin-antiovalbumin (OV-anti-OV) immune complexes, and opsonized latex particles all induced PMN swelling. The OV-anti-OV immune complexes were effective, whether prepared at antigen-antibody equivalence (insoluble) or at 4 or 9 times antigen excess (soluble). Swelling of PMN occurred at 37 degrees C, but not at 4 degrees C. Complement was not present in any of the experiments. In contrast to the above results, native IgG, OV-anti-OV F(ab')2 immune complexes and unopsonized latex particles did not induce PMN swelling. These results suggest that the PMN swelling observed in this study is due to Fc-dependent, complement-independent membrane stimulation and/or phagocytosis.

Polyethylene glycol enhances the binding of C1q to circulating immune complexes

By radioimmunoassay we measured the amount of endogenous C1q that was precipitated by polyethylene glycol (PEG) under the conditions of the 125I-C1q-binding test (C1q-BT). We found a linear correlation between the percentage endogenous C1q that was precipitated and the 125I-C1q-binding activity (C1q-BA). We concluded that the 125I-C1q behaves like the endogenous C1q. To detect circulating immune complexes (CIC) which had already bound C1q, human sera were added to tubes coated with anti-C1q. Under the conditions used, no C1q-bearing CIC were detected. In addition, 7 sera from patients with high C1q-BA were analyzed by sucrose-gradient ultracentrifugation. No C1q was found in the fast sedimenting fractions, although C1q-BA was detected in these fractions. With IgG-coated tubes we observed that PEG enhanced the binding of 125I-C1q as well as endogenous C1q to aggregated and monomeric IgG. PEG also enhanced the binding of CIC to C1q-coated tubes. The results suggest that CIC detected by the C1q-BT do not bear C1q in significant amounts in the circulation and that these CIC become detectable only in the presence of PEG.