Regulation of in vitro anti-DNA antibody production by a novel disease modifying anti-rheumatic drug, Lobenzarit

Lobenzarit (CCA) is a novel disease modifying anti-rheumatic drug. Although CCA has been shown to prevent the development of the autoimmune disorders in NZB/W F1 mice and in MRL/l mice, the precise mechanism of its action has not yet been clarified. The current study examined the effect of CCA on the in vitro production of anti-DNA antibody, a hallmark of the autoimmune disorders. In vitro anti-DNA antibody production was induced from highly purified B cells of normal human individuals by stimulation with Staphylococcus aureus and CD4+ T cells or with immobilized anti-CD3 activated CD4+ T cells. CCA suppressed the production of anti-DNA antibody as well as IgM at pharmacologically obtainable concentrations (10-50 micrograms/ml). CCA did not inhibit the initial stages of B cell activation in either culture system, but rather suppressed the maturation of previously activated B cells. Although CCA suppressed IL2 production by immobilized anti-CD3 activated CD4+ T cells, its suppressive effects on B cells were not overcome by the addition of IL2 or factors generated from mitogen activated T cells (TF). CCA did not suppress IL6 production by immobilized anti-CD3 activated CD4+ T cells nor that by B cells activated with SA+ IL2. These results indicate that CCA suppresses the production of anti-DNA antibody by directly inhibiting activated B cells. The data therefore suggest the possible efficacy of CCA in suppressing the function of activated B cells in human SLE patients.

Allotype-dependent stimulation of peripheral blood and synovial lymphocytes by IgG3 in rheumatoid arthritis

The immunopathologic process of rheumatoid arthritis (RA) is primarily expressed in the synovium where rheumatoid factor (RF) synthesis is concentrated. We hypothesized that RF synthesized by rheumatoid synovial cells (RSC) may be driven via a T cell-mediated immune response developed against IgG3 epitopes. To identify and characterize specific RSC RF epitopes and T cell antigens, two 28 amino acid peptides homologous with the C-terminus of IgG1 (P1) and IgG3 [G3m(5)] (P3) were synthesized and used in RF-binding studies and lymphocyte proliferation assays. Our results indicate that (i) the C-terminus of the CH3 domain contains epitopes for IgG3-reactive RSC RF; (ii) IgG3-reactive RSC RF binds primarily to IgG3 [G3m(5)]; (iii) P3 stimulated proliferation of T lymphocytes from both RA peripheral blood and RSC; and (iv) RF production was enhanced by P3 in selected RA cell cultures. These observations suggest that the C-terminus of IgG3 allotype G3m(5) may be important in T cell activation and RF production in RA.

CD7- T cells in rheumatoid arthritis

OBJECTIVE

Rheumatoid arthritis (RA) is characterized by decreased expression of CD7 in the peripheral blood and in the synovium. The present study was designed to identify the basis for and functional consequences of this decreased expression.

METHODS

Peripheral blood lymphocytes from normal controls and from patients with RA or systemic lupus erythematosus (SLE), and T cell lines derived from rheumatoid synovium, were evaluated using 3-color fluorescence-activated cell sorter analysis.

RESULTS

Normal subjects and most SLE patients expressed homogeneous, bright CD7 on CD4+, CD45RA+ cells, whereas RA patients demonstrated a significantly increased proportion of CD7- cells. T cell lines derived from rheumatoid synovium demonstrated a striking deficiency of CD7 on CD4+, CD45RA- cells. CD4+, CD45RA+ cells from RA patients changed phenotype after in vitro activation to CD45RA negativity, with up-regulation of CD7. CD7-, CD4+, CD45RA- cells were assessed for their ability to induce pokeweed mitogen-driven IgM and IgM-rheumatoid factor synthesis, and they were found to be potent helper/inducer cells. An increased population of CD7-, CD4+ cells in peripheral blood was found to predict a low response to recall antigens.

CONCLUSION

The low expression of CD7 in RA may explain some of the immune abnormalities which may contribute to the pathogenesis of this disease.

Mapping rheumatoid factor binding sites using genetically engineered, chimeric IgG antibodies

We are using chimeric IgG antibodies consisting of murine variable regions joined to human constant regions as rheumatoid factor (RF) binding substrates to localize and map IgM RF binding sites on IgG. Using chimeric antibodies in a modified RF ELISA, we showed that RFs from rheumatoid arthritis (RA) and Waldenstrom's macroglobulinemia (WMac) patients differ in their binding specificities for IgG3, although some of these RFs share common specificity for IgG1, IgG2, and IgG4. By shuffling constant region domains between IgG3 and IgG4, we showed that sequence variation in the CH3 domain is responsible for WMac-derived RF differentiation of IgG3 and IgG4. By making site-directed mutations in the wild-type IgG3 or IgG4 human gamma constant genes, we showed that His-435 is an essential residue in RF binding to IgG for most WMac RFs. The allotypic polymorphism in IgG3 at 436 is not responsible for differences in previous reports of high-frequency IgG3 binding by WMac RFs. A amino acid loop in the CH2 domain of IgG4 proximal to the CH2-CH3 interface is important in WMac RF binding to IgG; a more distal CH2 loop in CH2 has a more variable effect on WMac RF binding. To evaluate the contribution of the N-linked carbohydrate moiety at Asn-297 to RF binding sites on IgG, we measured RF binding to aglycosylated IgG antibodies produced by mutating the glycosylation signal Asn-297 to another amino acid. Of all four IgG subclasses, only aglycosylated IgG3 was a better RF binding substrate than its glycosylated subclass counterpart.(ABSTRACT TRUNCATED AT 250 WORDS)

A human monoclonal IgA rheumatoid factor using the VkIV light chain gene

A human hybridoma stably secreting IgA rheumatoid factor (RF) was produced by cell hybridization with peripheral blood lymphocytes of a patient with rheumatoid arthritis. The RF was of the IgA1 isotype with kappa-light chains and was useful for standardization or specificity controls in class-specific RF assays. RF activity was detected only when the IgA molecular were in a polymeric state, and could be measured by enzyme linked immunosorbent assay as well as in conventional agglutination based tests. The RF had the modified Ga fine specificity described previously for several RFs and for protein A. The immunoglobulin V genes used were isolated and sequenced. The light chain was encoded by the VkIV gene rearranged to Jk2; compared to the published VkIV germ line gene there was 90% nucleotide homology. The heavy chain gene used belonged to the VHI family and was rearranged to JH4. Comparisons with published sequences revealed 90% homology with the recently characterized VH gene expressed by RF-TS3, a rheumatoid synovia RF hybridoma.

Monoclonal IgM rheumatoid factors bind IgG at a discontinuous epitope comprised of amino acid loops from heavy-chain constant-region domains 2 and 3

A combination of site-directed mutagenesis and exon exchange has been used to further define the structure on IgG recognized by monoclonal IgM rheumatoid factors (RFs) from patients with Waldenstrom macroglobulinemia. Most of these RFs bound IgG1, -2, and -4 but not IgG3. For these RFs, His-435 is a critical residue for binding and replacing it with arginine, the residue present in IgG3, destroys or reduces RF binding. However, additional polymorphic sequences in both the heavy-chain constant-region domains (CH) 2 and 3 are important for RF binding. Among the important residues in CH2 are amino acids 252-254 and 309-311, which are conserved among IgG isotypes and comprise two loops of amino acids on the surface of the domain. Therefore, at least three regions, two from CH2 and one from CH3, contribute significantly to the epitope recognized by the RFs. Although this epitope contains many of the same residues as the staphylococcal protein A binding site on IgG, the binding specificities of staphylococcal protein A and monoclonal RFs are not identical. Sera from patients with rheumatoid arthritis contain antibodies directed not only at this epitope but also at other sites on IgG.

Rheumatoid arthritis serum or synovial fluid and interleukin 2 abnormally expand natural killer-like cells that are potent stimulators of IgM rheumatoid factor

We show that rheumatoid arthritis (RA) serum or synovial fluid (SF) increases the growth capacity of normal, interleukin 2 (IL-2) driven cell preparations, compared to normal human serum (NHS). Proliferation in RA serum and SF cultures was primarily associated with expansion of natural killer (NK)-like cells (CD16+, CD57+), and in NHS cultures, with T cell (CD3+ CD4+ CD8+) growth. The capacity of RA serum to promote NK cell growth was related to patient global clinical activity and rheumatoid factor (RF) titers. The NK-like cells, but not the T-like cells, induced high levels of IgM RF synthesis in autologous B cells. Thus, alteration in NK cell growth may disrupt NK-B cell circuits in RA and contribute to B cell dysfunction (RF synthesis).

The B cell repertoire in rheumatoid arthritis. III. Preferential homing of rheumatoid factor-producing B cell precursors in the synovial fluid

OBJECTIVE

We sought to compare the frequencies of precursors producing IgM rheumatoid factors (IgM-RFs) in synovial fluid and peripheral blood B cells from patients with rheumatoid arthritis (RA).

METHODS

We used limiting-dilution analysis of Epstein-Barr virus-activated B cells from seropositive and seronegative patients. B cell precursors producing IgM against insulin, an irrelevant autoantigen, were also assessed for comparison.

RESULTS

On average, IgM-RF-producing precursors were 15-fold higher in the synovial fluid than in the peripheral blood of seropositive RA patients, but not in seronegative RA patients. The frequency of B cell precursors producing IgM against insulin was lower in the synovial fluid than in the peripheral blood of both the seropositive and the seronegative patient groups; moreover, the concentrations were similar in both groups.

CONCLUSION

The findings provide evidence against a nonspecific accumulation of IgM-producing cells in the synovial fluid, and suggest that there is an active attraction of the RF-producing B cell precursors toward sites of inflammation in RA.

Regulation of antibody production mediated by Fc gamma receptors, IgG binding factors, and IgG Fc-binding autoantibodies

Fc receptors (FcRs) are immunoglobulin-binding structures that enable antibodies to perform a variety of functions by forming connections between specific recognition and effector cells. Besides eliciting cytotoxicity, inducing secretion of mediators and endocytosis of opsonized particles, FcRs are involved in the regulation of antibody production, both as integral membrane proteins and as soluble molecules released from the cell surface. Most FcRs belong to the same family of proteins as their ligands (immunoglobulin superfamily). This review contains recent data obtained by use of monoclonal antibodies and cloning studies on FcRs and FcR-like molecules. The importance of fine specificity of receptor binding site(s)--that of the conformation of FcRs and their ligands in triggering signaling mechanisms--is analyzed. The regulatory function of membrane-bound and -released FcRs; the correlation between cell cycle, FcR expression, and release; as well as the possible mechanisms of these phenomena are discussed.

Binding characteristics of human hybridoma IgG and IgM rheumatoid factors: influence of IgG isotype and carbohydrate content

The interaction of human monoclonal rheumatoid factors (RF) with the Fc portion of IgG is complex. We have investigated the influence of the nature of the antigen (Fc) on the binding of hybridoma-generated RF derived from patients with rheumatoid arthritis or systemic lupus erythematosus. For IgM RF, the interaction is strongly influenced by the primary structure of the Fc with little or no effect of the carbohydrate, which is positioned at amino acid 297 in the gamma-2 domain. In contrast, our preliminary data suggest that IgG RF binding is affected both by the primary structure and the nature of the carbohydrate of the Fc. These results suggest that the antigen selection events which lead to the induction and production of IgG RF are likely to be different from those that induce IgM RF production.

Generation and characterization of two monoclonal self-associating IgG rheumatoid factors from a rheumatoid synovium

OBJECTIVE

To study IgG rheumatoid factor (RF) from rheumatoid synovium.

METHODS

We fused the K6H6/B5 human-mouse heterohybridoma with unstimulated rheumatoid synovial B cells to generate IgG-RF-secreting hybridomas.

RESULTS

The RFs from 2 such hybridomas bound specifically to the Fc fragment of human IgG and self-associated to form immune complexes. Such immune complexes are a major characteristic of the pathogenic IgG-RFs in rheumatoid synovium.

CONCLUSION

IgG-RF-secreting hybridomas have been obtained. Analyses may reveal the underlying mechanisms of the induction of IgG-RF.

Interleukin 6 levels in synovial fluids of patients with different arthritides: correlation with local IgM rheumatoid factor and systemic acute phase protein production

Interleukin 6 (IL-6), a multifunctional cytokine particularly active in regulation of the acute phase response, governs the terminal maturation of B lymphocytes and participates in early activation of T cells. IL-6 levels of synovial fluids of 153 patients with different arthritides were measured by a simple sandwich enzyme immunoassay. Highest IL-6 concentrations were detected in patients with rheumatoid arthritis (RA), particularly in those characterized by very active general symptoms and severe joint pain. High IL-6 levels were detected in patients with juvenile RA with polyarticular onset of disease and in gout. Corresponding to the suggested in vivo relevance of IL-6, dose correlation of IL-6 levels with the synovial IgM rheumatoid factor accumulation was demonstrated. The rate of the correlation between synovial IL-6 level and concentration of serum C-reactive protein in RA was inversely proportional to the dose of steroid treatment in patients with RA.

Induction of IgM and IgM-rheumatoid factor synthesis in vitro by indomethacin

Indomethacin, which is thought to exert its therapeutic effect by inhibiting the synthesis of PGE2, is a commonly used first-line agent in the treatment of rheumatoid arthritis (RA). However, the effect of this drug on the humoral immune response in RA remains unclear. In this study, modulation of the in vitro synthesis of IgM and IgM-rheumatoid factor (RF) by indomethacin and prostaglandin E2 was examined in 11 patients with active RA and 10 normal controls. Indomethacin at a final concentration of 1 microgram/ml significantly enhanced IgM production (P less than 0.01) and RF production (P less than 0.02) in Staphylococcus aureus Cowan I (SAC) stimulated RA cultures when compared to controls in whom no net enhancement effect was observed. In the patients, this increase in IgM production was more pronounced than the corresponding increase in RF synthesis (P = 0.078), suggesting that IgM and IgM-RF-secreting RA plasma cells have different susceptibilities to PGE2 mediated suppression. Nonetheless, addition of PGE2 (10(-8) M final concentration) to the cultures inhibited IgM and RF production to a similar degree in the patient and control cultures. These findings demonstrate that PGE2 causes suppression of IgM and IgM auto-antibody production in vitro and that inhibition of endogenous PGE2 synthesis in RA patients treated with indomethacin results in a marked increase in the production of these antibodies.

Framework peptides from kappa IIIb rheumatoid factor light chains with binding activity for aggregated IgG

Most monoclonal human rheumatoid factors (RF) and some RF from rheumatoid patient's synovia are restricted in their light chains, using predominantly the kappa IIIb subfamily. Very few sequence differences are found between these light chains. Light chains with similar variable region framework sequences are also found in some mouse monoclonal RF derived from mice stimulated with lipopolysaccharide or secondarily immunized with protein antigens. There are two likely explanations for this restriction in framework sequences between the two species: (a) the sequences are important for the immunoregulation of RF production or (b) the sequences are concerned with the antibody binding specificity of the RF. We have examined overlapping octapeptides from the kappa IIIb light chain variable region and show that some framework peptides have the ability to bind aggregated IgG. Replacement of amino acids within the peak binding peptide have indicated the critical amino acids necessary for binding.

Defective immune adherence and elimination of hepatitis B surface antigen/antibody complexes in patients with mixed essential cryoglobulinemia type II

Mixed essential cryoglobulinemia type II (monoclonal Ig/polyclonal IgG) is characterized by systemic vasculitis caused by the deposition of circulating immune reactants that include the monoclonal component. Such reactants may include immune complexes (IC) formed from exogenous Ag. IC binding to E C receptor type 1 appears to play a role in transport and buffering of such IC (immune adherence: IA). To define the mechanisms responsible for immune deposition, 7 patients with cryoglobulinemia type II (IgM kappa/polyclonal IgG) and 14 normal volunteers were injected i.v. with hepatitis B surface Ag/antibody complexes. Two minutes after injection, only 19.4% (mean) of the circulating complexes were bound to E in patients as compared with 63.1% in normal subjects. This IA correlated directly with C4 and inversely with the IgM rheumatoid factor (RF) titer. Disappearance of IC was faster in patients (mean elimination rate: 15.7%/min) than in normal subjects (9.3%). In vitro experiments demonstrated that C depletion, interference with IC opsonization by monoclonal IgM RF, and decreased binding of opsonized IC in the presence of monoclonal RF are each associated with decreased IA. These observations suggest that, in patients with cryoglobulinemia type II, monoclonal IgM RF and low C contribute to reducing IA of circulating IC that might be rapidly trapped in tissues, resulting in injury.

Subclass distribution and size of human IgA rheumatoid factor at mucosal and nonmucosal sites

Elevated serum levels of IgA, IgA1, and IgA2 rheumatoid factors (RF) were demonstrated by enzyme-linked immunosorbent assay in 69%, 73%, and 36%, respectively, of 100 patients with rheumatoid arthritis (RA), whereas fewer than 5% of 100 healthy donor sera contained elevated levels of these RFs. In serum samples from 125 controls with 4 different chronic diseases (systemic lupus erythematosus, ankylosing spondylitis, bronchial asthma, and polyarteritis nodosa), levels of IgA-, IgA1-, and IgA2-RF were found to be increased in 7%, 7%, and 8%, respectively. Comparison of RF levels in samples of serum, synovial fluid (SF), and saliva from RA patients indicated local production of both IgA-RF subclasses in salivary glands and in synovial tissue. Significant positive correlations were found between levels of IgA-RF subclasses in SF and serum, but not in serum and saliva or in SF and saliva. Fractionation of serum, SF, and saliva from patients with RA (by high performance liquid chromatography under acidic conditions) demonstrated that both IgA subclasses with RF activity occur mainly in fractions that also contain IgM. The results of this study show that 1) IgA-RF in serum and SF is mainly of IgA1 subclass, 2) both IgA-RF subclasses are produced locally in salivary glands and in synovial tissue, 3) the production of both IgA-RF subclasses at mucosal and nonmucosal sites is independent from each other, and 4) both IgA-RF subclasses occur predominantly in polymeric form in serum, SF, and saliva in RA patients.

Correlation between rheumatoid factor and IL-6 activity in synovial fluids from patients with rheumatoid arthritis

Synovial fluids (SF) and sera (S) from patients with rheumatoid arthritis (RA) were examined for IgM, IgM-rheumatoid factor (IgM-RF), albumin and interleukin-6 (IL-6) activity. The quotient of SF/S IgM-RF was elevated compared with that of SF/S albumin in 7 patients with seropositive RA, although the quotient of SF/S IgM was lower than that of SF/S albumin. SF IL-6 activity was much higher than serum IL-6 activity in all the 7 RA patients. In synovial fluids from 22 seropositive RA patients, SF IL-6 activity was significantly correlated with the SF IgM-RF, IgG-RF and IgA- less than RF, but not with SF IgM, IgG or IgA. Moreover, SF IgM-RF as well as SF IL-6 activity was significantly correlated with the Westergren erythrocyte sedimentation rate (ESR) or the Lansbury articular index. These results indicate that IL-6 and RF might be produced within the rheumatoid joints as a result of abnormal immune system activation, which is associated with the disease activity of RA. Three of the 4 seronegative RA patients, however, showed high SF IL-6 without detectable levels of SF IgM-RF, indicating that IL-6 alone is not sufficient for IgM-RF production.

Expression of large quantities of rheumatoid factor major cross-reactive idiotype in the serum of adults with seropositive rheumatoid arthritis

We quantified rheumatoid factor cross-reactive idiotype (RF-CRI) in whole serum from RF+ rheumatoid arthritis (RA) patients, using an inhibition enzyme-linked immunosorbent assay which is not affected by the presence of IgG. Serum from 16 RF+ RA patients contained 2-252 micrograms/ml RF-CRI (geometric mean */divided by SD 20.8 */divided by 5.2), while serum from 11 normal adults contained 1-16 micrograms/ml RF-CRI (geometric mean */divided by SD 3.9 */divided by 2.3). Serum from 8 of the RF+ RA patients contained RF-CRI at concentrations more than 2 standard deviations above the geometric mean in the normal subjects (greater than 21 micrograms/ml). Our results indicate that some RF+ RA patients express high concentrations of RF-RCRI and immunoglobulin molecules that express the RF-CRI may not be RF.

New roles for rheumatoid factor

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Arthritis and nephritis in patients with systemic lupus erythematosus

Previous publications suggest that in patients with systemic lupus erythematosus (SLE), rheumatoid factor (RF) may be "protective" against nephritis. In our study of 662 patients with SLE, we found that persistent, rheumatoid-like arthritis showed a much stronger inverse correlation with nephritis than RF. Of 186 such patients, 59 developed clinically evident nephritis (32%) compared to 263 of the other 476 patients (55%) (p less than 10(-7). RF showed only a weak inverse relationship to nephritis (p = 0.064). We conclude that the presence of persistent rheumatoid-like arthritis in patients with SLE identifies a clinical subset of patients who are less likely to develop nephritis than those with no arthralgia, no objective arthritis or only episodic arthritis. We hypothesize that such patients represent a genetically determined subset among patients with SLE and that perhaps they are more likely to bear the HLA-DR4 allele.

Molecular analysis of IgM rheumatoid factor binding to chimeric IgG

To localize regions on IgG bound by rheumatoid factors (RF), we studied IgM RF binding to chimeric IgG antibodies consisting of murine V regions fused to human constant regions. Using a modified RF ELISA, we showed that polyclonal RF from rheumatoid arthritis patients bound IgG1, 2, and 4 strongly; IgG3 was also bound, although less well. The majority of 18 monoclonal RF from patients with Waldenstrom's macroglobulinemia bound IgG1, 2, and 4 only. In contrast to RF from RA, 14 of 18 monoclonal RF did not react with IgG3. Only 3 of 18 monoclonal RF bound IgG3 well. By shuffling C region domains between IgG3 and IgG4, we showed that sequence variation in the CH3 domain is responsible for the differential binding of monoclonal RF to IgG3 and IgG4. Hybrid IgG3/IgG4 antibodies containing the CH3 domain of IgG4 were bound by monoclonal RF, whereas those containing the CH3 domain of IgG3 were not. To evaluate the contribution of the N-linked carbohydrate moiety at Asn-297 to RF binding sites on IgG, we measured RF binding to aglycosylated IgG antibodies produced by mutating Asn-297 to another amino acid. Glycosylated and aglycosylated IgG1, 2, and 4 were bound identically by monoclonal and polyclonal RF. Aglycosylated IgG3, however, was bound better than glycosylated IgG3 by polyclonal RF and by IgG3-reactive monoclonal RF.

Heterogeneity in the reactivity of various groups of IgM antibodies with kaolin

Kaolin strongly adsorbed rheumatoid factor (RF) and mono-nucleosis antibodies, while cold agglutinins and some antimicrobial IgM antibodies were poorly adsorbed. Maximum adsorption took place at a pH of about 7. The degree of adsorption also depended on the amount of kaolin. Rheumatoid factor could be eluted from kaolin at pH 11 after adsorption at pH 7. The reported heterogeneity with regard to reactivity with kaolin is suggested to be due to hydrophobic interactions.

IgG binding of monoclonal anti-nuclear antibodies from MRL-lpr/lpr mice

To assess the specificity of anti-nuclear antibodies with cross-reactive rheumatoid factor (RF) activity, monoclonal anti-DNA and anti-Sm antibodies from MRL-lpr/lpr mice were tested for binding to a variety of IgG antigens. These antibodies had all been previously identified as binding heterologous IgG. By ELISA, antibodies in this panel all bound BALB/c myeloma proteins representing the different IgG subclasses, indicating broad reactivity with murine IgG as well as heterologous IgG. The determinant recognized by these antibodies was further investigated using the Fab, F(ab')2 and Fc fragments of both human as well as rabbit origin. All antibodies bound well to fragments as well as intact IgG antigens. These antibodies were further analysed by Western blotting, demonstrating that most bound to both heavy and light chains of human origin. Together, these observations suggest that some anti-nuclear antibodies bind a conserved antigenic determinant present widely on immunoglobulin chains. This determinant may represent a common sequence important in immunoglobulin domain structure.