Polyclonal Rheumatoid Factors Research Articles

A novel mass spectrometric-based proteomic approach challenges the current paradigm on cryoglobulin typing in the diagnostic laboratory

Cryoglobulins precipitate out of serum at temperatures lower than 37°C and can have serious clinical manifestations. They may be associated with haematological malignancies, chronic infections and autoimmune diseases. Traditional typing of cryoglobulins use the Brouet classification, depending on the presence or not of rheumatoid factor activity: type I (monoclonal immunoglobulin with no rheumatoid factor), type II (mixed cryoglobulin with monoclonal rheumatoid factor) and type III (mixed cryoglobulin with polyclonal rheumatoid factor). Current methods used to type cryoglobulins include electrophoresis and immunofixation. We describe a novel, streamlined workflow of cryoglobulin analysis using mass spectrometry (MS) to characterise the proteomic signatures [heavy chain complementarity-determining region 3 (HCDR3) regions] of cryoglobulins. This provides an extension to traditional immunochemical methods of analysis and offers increased sensitivity; monitoring capacity by HCDR3 regions at the amino acid level; and clinical applications. Outstandingly, MS analysis offers predictive value by detecting the presence of pathogenic clonotypes before the onset of clinical manifestations. We highlight its applicability and benefits through clinical cases, demonstrating the greater ability to molecularly characterise cryoprecipitates in a similar turn-around time to current methodology. Work to establish clinically relevant libraries of antibody clonotypes is currently underway.

Occurrence of two germline-related rheumatoid factor idiotypes in rheumatoid arthritis and in non-rheumatoid seropositive individuals

Human rheumatoid factor (RF) paraproteins express two distinct light chain cross-reactive idiotypes defined by the monoclonal antibodies 17.109 and 6B6.6. These germline gene-related cross-reactive idiotypes are both carried on VK3 light chains and are each present on about one-third of IgM RF paraproteins. We assessed the degree to which these idiotypes are represented in polyclonal RFs. We used rheumatoid arthritis (RA) and non-RA RF-positive sera selected from a large cross-sectional population study (the Mini-Finland Health Survey), and sera from a community-based follow-up study of recent-onset RA patients from Heinola, Finland. In the Mini-Finland Health Survey, elevated levels of the 17.109 RF idiotype were seen in sera of 13% of the RA and 19% of the non-RA group; 6B6.6 RF was seen in 26% of the RA and 28% of the non-RA group. In sera of the Heinola follow-up study, 17.109 RF was seen in 12% initially, but in only 3% at 8 years. Similarly, 6B6.6 RF was detected in 25% initially, but in only 7% at 8 years. Ten sera positive for RF prior to the onset of clinical RA were identified from individuals of a second large population study from Finland (North Karelia project); two of these sera exhibited the 6B6.6 idiotype; none exhibited the 17.109 idiotype. The data are consistent with the concept that these germline gene-related cross-reactive RF idiotypes occur frequently in the polyclonal RF of non-RA as well as RA sera, and that in RA the idiotypes may sometimes be reduced or lost as a consequence of somatic diversification of the RF through somatic mutation, usage of new germline genes, or both.

IL-2 enhances polyclonal IgM but not IgM-rheumatoid factor synthesis by activated human peripheral blood B cells.

IgM-rheumatoid factor (RF) is thought to be involved in the pathogenesis of rheumatoid arthritis (RA). Several cytokines are known to regulate immunoglobulin synthesis. In this study the effects of IL-2 on polyclonal IgM and IgM RF synthesis were compared. Cytokines were added to peripheral blood B cells from normal subjects and patients with RA after activation by Staphylococcus aureus Cowan 1 (SAC). The addition of IL-2, but not IL-4 or IL-6, resulted in significant enhancement of IgM synthesis in cultures from both healthy subjects and patients with RA. Similar degrees of enhancement were seen in both peripheral blood mononuclear cell and highly purified B cell cultures. IgM-RF was synthesized after activation in cultures from healthy subjects and spontaneously in cultures from RA patients. In contrast to polyclonal IgM synthesis, IL-2 failed to augment IgM-RF synthesis in cell cultures from either healthy subjects or RA patients. This study demonstrates different effects of IL-2 on IgM and IgM-RF synthesis.

Cross-reactive rheumatoid factors inrheumatoid arthritis with extra-articular disease

Rheumatoid factors (RF) have been shown to have considerable heterogeneity and bind with IgG as well as with a variety of substances such as nuclear histone, non-histone nuclear protein, nitrophenyl groups or ssDNA. We describe evidence that polyclonal RF cross-reactive with ssDNA (CRRF) are widely distributed in a variety of rheumatic diseases, and that their serum level is significantly higher in rheumatoid arthritis (RA) with extra-articular disease. Although the mechanism of the cross-reactivity is not clear, the presence of CRRF could be a serological feature of a clinical subset of RA. The high prevalence rate of CRRF in RA with extra-articular disease also suggests its pathogenetic role in the extra-articular manifestation of this disease.

Quantification of cross-reactive idiotype-positive rheumatoid factor produced in autoimmune rheumatic diseases. An indicator of clonality and B cell proliferative mechanisms

The aetiology of sustained autoantibody production in human autoimmune diseases is unknown. Evidence for structural similarities and common clonal origin among autoantibodies have been demonstrated through the expression of cross-reactive idiotype (CRI). In the present study we use four monoclonal antibodies (MoAbs) with specificity for non-overlapping CRI on human rheumatoid factor (RF) autoantibodies to define the structural features of polyclonal RF characteristic of patients with autoimmune rheumatic diseases. The pattern of CRI expression in the serum of 12 patients with rheumatoid arthritis (RA), eight with systemic lupus erythematosus (SLE) and 20 with primary Sjögren's syndrome and 34 normal individuals were determined in parallel with the level of IgM RF, IgA RF and autoantibodies to the cellular antigens SS-A, SS-B, Sm, nRNP and dsDNA and cryoglobulins. The results demonstrate significant elevation in the level of IgM and IgA expressing VHI (G6 and G8) and VHIII (B6 and D12) associated CRI in the serum of patients with autoimmune rheumatic diseases compared with normal individuals. These increases paralleled, but did not equal the increase in the level of immunoglobulins and RF. However, when expressed as proportion of immunoglobulin, only the VHI-associated CRI were significantly elevated in patients compared with normal individuals. The proportion of IgM RF expressing the VHI-associated CRI was higher in patients with Sjögren's syndrome compared with SLE and RA. Furthermore, the proportion of IgA RF expressing the G6 CRI was higher than G6+ IgM RF. These findings imply that different mechanisms contribute to RF production in autoimmune diseases. It is suggested that polyconal B cell activation is likely to be a contributing mechanism. However, such polyclonal activation is unlikely to be random since a selective elevation in the level of specific autoantibodies and VHI-associated CRI is observed. Furthermore, the data demonstrate that a proportion of autoantibodies in autoimmune diseases are immunoglobulin germline gene encoded. This is more evident in some patients with primary Sjögren's syndrome, where RF is likely to be oligoclonal or monoclonal in individuals with lymphoproliferation.

Natural History and Clinical Impact of Cryoglobulins in Chronic Hepatitis C: 10-Year Prospective Study of 343 Patients

Serum cryoglobulins (CGs) are present in patients with chronic hepatitis C virus (HCV) infection, but their long-term clinical importance has not been established. We assessed the development rates, morbidity, and influence on the evolutionary course of hepatitis C of CG. A cohort of 343 HCV-RNA seropositive outpatients (173 men; age, 58 y; 82 with cirrhosis; 61 treated with interferon) with persistently increased aminotransferase levels and histologically defined liver disease was investigated. Patients initially were investigated for the presence, amount, and type of CG and prospectively followed up with clinical and laboratory examinations every 6 months. At enrollment, CGs were found in 163 (47%) patients at a mean level of 173 +/- 142 mg/L; 80% were type III, and associated to female sex (61% vs 40%, P = .0002) and cirrhosis (29% vs 19%, P = .04). Over the course of 17-130 months (median, 116 mo), de novo CG developed in 25 patients (2.3% per year), including 5 with cryoglobulinemic syndrome (.3% per year). The 10-year rates of progression to cirrhosis and of liver and extrahepatic complications were similar in CG (+) and CG (-) patients (32% vs 34%; 23% vs 16%; 5% vs 3%). The 10-year survival rates were lower for cirrhotic than for noncirrhotic patients (57% vs 91%, P < .00001), independently of CGs. CGs are common in patients with chronic HCV infection, mainly are type III, and do not influence the clinical course of hepatitis C during the first decades, except for the few rare cases of cryoglobulinemic syndrome.

56-Year-Old Man With Rash, Abdominal Pain, and Arthralgias

56-Year-Old Man With Rash, Abdominal Pain, and Arthralgias

Mechanisms of renal damage in mixed cryoglobulinaemia nephritis.

Mixed cryoglobulinaemia (MC) is a systemic disorder characterized clinically by the typical triad of purpura, arthritis and weakness, and serologically by the presence of cryoprecipitating complexes, formed by a monoclonal or polyclonal rheumatoid factor and polyclonal immunoglobulins. The presence of anti-HCV antibodies and viral mRNA in the serum of MC patients has shed new light on the pathogenesis of the disease. However, the mechanisms leading to the different manifestations of MC are still unknown.

Type II mixed cryoglobulinaemia, hepatitis C virus infection, and glomerulonephritis.

Mixed cryoglobulins (MC) are immunoglobulins which precipitate reversibly in the cold. Type II mixed cryoglobulins are composed of a monoclonal component (usually IgMk) with rheumatoid factor (RF) activity against polyclonal IgG. In type III MC, all the components are polyclonal. The majority of MC are secondary to connective tissue diseases, infectious or lymphoproliferative disorders, hepatobiliary diseases, or immunologically mediated glomerular diseases. The aetiology of MC is not clear and cryoglobulinaemia was considered 'essential' until an association between hepatitis C virus (HCV) infection and MC was recognized. The renal pattern includes typical glomerular lesions characterized by a particular glomerular monocyte infiltration, double-contoured appearance of the glomerular basement membrane (GBM) and by the presence of intraluminal 'hyaline thrombi' due to deposition of circulating cryoglobulins. The progression of renal disease is variable: in one-third of patients remission of renal symptoms occurs, 20% of patients experienced nephritic or nephrotic flare-ups during the course of the disease. Uraemia is observed in only 10% of patients 10 years after renal disease onset, but 50% of patients had already died from cardiovascular disease, infectious liver failure, or neoplasia during those 10 years. This review analyses the pathogenic mechanisms of MC and associated GN, with particular attention to the role of HCV infection. HCV RNA is detected in most patients with MC. HCV, by infecting B cells, could trigger abnormal production of polyclonal RF in type III MC and, together with other factors, a clone selection of B cells to produce monoclonal IgMk RF in type II MC. The presence of IgMk in serum appears essential for glomerular damage to occur. Cryoglobulinaemic GN might be initiated by IgG antibody-HCV complexes binding to IgMk RF, either in situ or in circulation, nephrotoxicity being due to a particular affinity of the IgMk RF for cellular fibronectin present in the mesangial matrix. Glomerular damage can be perpetuated by the reduced effectiveness of monocytes to remove cryoglobulins.

Monozygotic Rheumatoid Arthritis Twin Pairs Express Similar Levels of Conserved Immunoglobulin V Gene in Polyclonal Rheumatoid Factors Irrespective of Disease Status

The degree of polyclonal RF heterogeneity was assessed in diseased and non-diseased twins with rheumatoid arthritis (RA). The distribution of variable region determinants encoded by a set of immunoglobulin germline, or minimally mutated germline, genes within IgM RF, IgG RF and IgA RF isotypes was determined by ELISA using specific mouse monoclonal antibodies (MoAb) in fractionated plasma from 12 members of six monozygotic twin pairs with RA. The results reveal that at least 40% (range approximately 18-87%) of IgM RF are encoded by a small set of approximately 10 genes from the VH1, 3 and 4 families. Furthermore, a significant proportion of IgG RF and IgA RF (approximately 30%) are also encoded by these same genes. Comparison with RF-negative fractions of immunoglobulins showed that the examined variable region determinants were overrepresented in the RF fractions. The level of expression of the variable region determinants in RF were generally similar within twins but different between unrelated twin pairs irrespective of disease status. The variability of VH gene usage between unrelated individuals suggests that the level of expression and regulation of the variable region determinants may be genetically regulated or influenced by common environmental factors.

Cryoglobulinemic glomerulonephritis: A membranoproliferative glomerulonephritis induced by hepatitis C virus

Mixed cryoglobulins (MCs) are proteins that precipitate from cooled serum, and are composed of a polyclonal immunoglobulin G (IgG) bound to another immunoglobulin that acts as an anti-IgG rheumatoid factor (RF). In type II mixed cryoglublinemia, the antiglobulin component, usually of the IgM class, is monoclonal; it is polyclonal in type III mixed cryoglobulinemia. The majority of MCs are found in patients with connective tissue diseases, infectious or lymphoproliferative disorders, hepatobiliary diseases, or immunologically mediated glomerular diseases (secondary MCs). The etiology is not clear for 30% of all MCs, and this type of cryoglobulinemia is called “essential.” There is a common clinical syndrome in types II and III essential mixed cryoglobulinemia (EMC) characterized by purpura, weakness, and arthralgia. In type II EMC only, in which an IgMk is the monoclonal RF, a membranoproliferative glomerulonephritis (MPGN) occurs with some peculiar morphologic and clinical features; this is termed “cryoglobulinemic GN.” Glomerulonephritis can be differentiated from idiopathic MPGN, especially in the acute stage, which is characterized by an acute nephritic syndrome, by the following findings: (1) the presence of large deposits filling the capillary lumen that sometimes are shown to have a characteristic fibrillar or crystalloid structure by electron microscopy; (2) the extent of the exudative component consequent to the frequently massive infiltration of monocytes; (3) a more diffuse and evident thickening of the glomerular basement membrane, which has a double-contoured appearance that is mainly due to the peripheral interposition of monocytes, with less evident mesangial expansion; and (4) possibly some vasculitis in small and medium-sized renal arteries without concomitant features of segmental necrotizing GN or crescentic GN. The proposed pathogenetic mechanisms for EMC and for the renal damage that occurs in type II EMC are analyzed in this review, with special emphasis on the role of hepatitis C virus (HCV) infection. Hepatitis C virus antibodies and HCV RNA (indicating active viral infection) are detected in the majority of cases with essential and secondary MCs. It has been suggested that by infecting the B cells the virus may trigger abnormal production of the polyclonal RF component of the cryoglobulins in type III MCs and, in association with some other unidentified factors, may induce abnormal proliferation of a special clone that produces the monoclonal RF component in type II MCs. Cryoglobulinemic MPGN occurs only when this monoclonal RF (usually an IgMk) is produced as a consequence of the HCV infection. The presence in the serum of an IgMk RF with specific, as yet unknown characteristics seems to be essential for the development of the glomerular damage associated with HCV infection, although the possibility that HCV can induce an immune complex-mediated MPGN independently of the induction of type II MCs (as hepatitis B virus does) cannot be ruled out. Cryoglobulinemic GN might be initiated by a binding either in situ or in the circulation of IgG antibodies-HCV complexes to IgMk RF, the nephrotoxicity being due to a particular affinity of the IgMk RF for the glomerular matrix. The potential role of interferon-alpha in the treatment of mixed cryoglobulinemia associated with HCV and of cryoglobulinemic GN is emphasized.

Rheumatoid-factor-reactive sites on CH 3 established by overlapping 7-mer peptide epitope analysis

Polyclonal IgM rheumatoid factors (RF) from ten patients with rheumatoid arthritis and six monoclonal IgM RF were isolated from monomeric IgG affinity columns and studied for their reactivity with the entire CH 3 domain of IgG synthesized as overlapping 7-mers using a pin-ELISA assay. All ten polyclonal IgM RF showed similar profiles of reactivity which included peptides with solvent accessible residues PREPQVY (residues 343–349), PQVYTLP (residues 346–352), TLPPRSE (350–356), DGSFFLY (401–407), WQQGNVF (417–423), CSVMHEG (425–430), EGLHNHY (430–436) and KSLSLSP (439–446) of the CH 3 domain. Substitution of a neutral glycine or alanine for each residue within these RF-reactive epitopes indicated that tyrosine at position 349, prolines at 343, 346 and 352, glutamine 347, valine 348, threonine 350, leucine 351, arginine 354, aspartic acid 401, tyrosine 407, serine 426, histidine 429, leucine 432, tyrosine 436 and lysine 439 represented important single amino acids within CH 3 for RF reactivity. Regions of CH 3 primary sequence with and without the single allotype-specific amino acid substitutions of glycine for alanine 431 (Gmx) or aspartic acid for glutamic acid (356) and leucine for methionine (358) (Gma) often showed considerable differences in reactivity with individual polyclonal and monoclonal RF. However, these differences in RF reactivity did not correlate with the individual anti-Gm RF specificity. Assays using monoclonal IgM RF produced from RA synovial B cells or peripheral blood B cells frequently showed a much more restricted spectrum of reactive CH 3 epitopes. 7-mer peptides representing RF-reactive sites on CH 3 preincubated with polyclonal IgM RF showed strong inhibition (55–66%) of RF binding to whole IgG on the ELISA plate. These studies indicate that it is possible to define portions of the IgG CH 3 domain participating in the reaction with IgM RF using reactive epitope-mapping with sequential linear peptides derived from the primary IgG CH 3 sequence.

Analysis of the V kappa III Variable Regions of Polyclonal Rheumatoid Factors Arising During Epstein Barr Virus Induced Infectious Mononucleosis

The mechanisms that govern autoantibody production are still under debate. In particular, auto-antibodies can appear as a consequence of a polyclonal activation of B cells or as a consequence of an antigen driven B cell expansion. The molecular analysis of the variable regions of auto-antibodies arising during different clinical situations can help to understand the origin of auto-antibodies. We recently described the main light chain variable regions of polyclonal rheumatoid factors occurring during rheumatoid arthritis and suggested that the mutation pattern of these regions could reflect an antigen driven process. Using the same approach, we now report the molecular analysis of the same light chain variable region containing a VKIII segment of rheumatoid factors originating from a polyclonal activation of B cells during an in vivo Epstein-Barr virus infection, infectious mononucleosis. The cDNA derived from rheumatoid factor synthetizing cells were amplified by two sets of polymerase chain reaction. The amplified products were cloned in M13mp19 phages and sequenced. The nucleotide analysis of the VKIII containing VK regions shows that: 1) the rheumatoid factor activity is associated with the 3 VKIII genes (Kv 325, Kv 328 and Vg) already known to encode for monoclonal and polyclonal rheumatoid factors, 2) there is a preferential use of Kv 328 and Vg, each one of these genes being poorly mutated, 3) the CDR mutation rates of these genes is no higher than the framework mutation rates, 4) there is a restriction of the JK usage; Kv 328 derived gene segments rearrange exclusively with JK1, Vg preferentially rearranges with JK1 and JK4. These results mainly suggest that naturally occurring polyclonal activation of autoreactive B cells produces poorly mutated autoantibodies.

Monoclonal IgM rheumatoid factors generated from synovial B cells of rheumatoid arthritis patients react with beta 2-microglobulin. Monoclonal RF react with beta 2m.

Four of 15 monoclonal human IgM rheumatoid factors (RF) derived from synovial B cells of patients with rheumatoid arthritis showed positive ELISA reactions with human beta 2-microglobulin. These findings were different from those previously noted using IgM RF derived from monoclonal Waldenstrom's paraproteins or the IgM components of mixed cryoglobulins, and resembled the anti-beta 2 microglobulin specificity of polyclonal IgM RF from patients with rheumatoid arthritis. Reactions of monoclonal IgM synovial RF with overlapping 7-mers of beta 2m sequence indicated major regions of positive reactivity at positions 57-64 and 89-95 which were maintained in the presence of high salt (300 mM NaCl) conditions. Glycine substitution of each residue within RF-reactive beta 2m regions indicated that tryptophanes at position 60 and 95, lysine at 58, phenylalanine at 62, valine at 93 and arginine at 97 constituted important single amino acids for the reactive epitopes. These findings indicate that clonally restricted human IgM RF derived from diseased tissues of patients with RA show anti-beta 2m reactivity similar to polyclonal RF from the same patients. This particular fine specificity is not present in monoclonal RF derived from patients with Waldenstrom's or mixed cryoglobulins showing anti-gamma-globulin activity.

A quantitative ELISA for measurement of rheumatoid factor associated cross-reactive idiotypes in serum from patients with rheumatic diseases.

A sensitive ELISA for the quantitation of RF associated cross-reactive idiotypes (CRI) has been developed. CRI bearing IgM was captured by immobilized F(ab')2 fragments of monoclonal anti-CRI antibodies and revealed with isotype specific conjugates. Factors affecting sensitivity, specificity and reproducibility of the assay were assessed. The sensitivity limit was less than 10 ng/ml and the linear assay range for the CRI standard curve was from 80 to 500 ng/ml. Using this ELISA system we have quantitated serum levels of the CRI in different groups of patients with RA, early synovitis and normal individuals. Our results indicate a significant increase in the levels of the CRI in the patient groups compared to the normal subjects tested, and suggest involvement of a diverse repertoire of Ig variable region germline genes and/or somatic mutation in production of polyclonal RF in RA.

Heteroclitic polyclonal and monoclonal anti-Gm(a) and anti-Gm(g) human rheumatoid factors react with epitopes induced in Gm(a-), Gm(g-) IgG by interaction with antigen or by nonspecific aggregation: a possible mechanism for the in vivo generation of rheumatoid factors

Heteroclitic rheumatoid factors (RF) are specific for allotypic determinants, e.g., Gm(a) or Gm(g) on allogeneic, but not autologous IgG. All polyclonal RF we isolated from nine rheumatoid arthritis patients with circulating Gm(a-), (b+), (g-), (f+) IgG displayed dual heteroclitic activity for the Gm(a) and Gm(g) allotypes, as shown by using appropriate RBC agglutination assays and affinity columns bearing Gm(a+) or Gm(g+) IgG. To investigate possible mechanisms underlying the in vivo generation of heteroclitic RF, we tested the ability of nonspecifically and immune-specifically aggregated Gm(a-), (g-) IgG to function as targets for RF from Gm(a-), (g-) patients with rheumatoid arthritis. Heat aggregation (63 degrees C for 20 min) or binding to Ag (as in tetanus toxoid-antitetanus toxoid complexes) induced a "functional" Gm(a+) and/or (g+) phenotype in Gm(a-), (g-) IgG from five healthy subjects and five rheumatoid patients, as suggested by the ability of these altered IgG to function as efficient targets for six heteroclitic RF in direct binding and competitive inhibition experiments. That heterocliticity and dual Gm(a), Gm(g) specificity can be features of a single antibody molecule was formally demonstrated by analysis of a monoclonal RF (IgM mAb 61) generated from a Gm(a-), (g-) rheumatoid patient. RF mAb 61 displayed a high affinity (Kd, 10(-7) M) for IgG Fc fragment of Gm(a+) and (g+) IgG or aggregated autologous Gm(a-), (g-) IgG but did not bind to native autologous IgG. To investigate the molecular basis of the acquired Gm(a) phenotype, PBMC from five Gm(a-) patients with rheumatoid arthritis and two Gm(a-) normal subjects arthritis and two Gm(a-) normal subjects were cultured in vitro after activation with PWM. In most instances, these PBMC produced IgG that behaved as Gm(a+) in sensitive ELISA. Application of the polymerase chain reaction (PCR), using probes specific for the nucleotide sequence coding for the Gm(a) tetrapeptide, to the amplification of DNA from the in vitro-stimulated Gm(a-) normals or rheumatoid patients' PBMC provided no evidence for Gm(a) nucleotide sequences. The present data suggest that acquisition of the Gm(a) determinant by Gm(a-) IgG may result from subtle changes in the CH2-CH3 RF-binding region. Such changes would occur when Gm(a) IgG are complexed with Ag or nonspecifically altered, thereby providing a possible explanation for the induction of heteroclitic RF in Gm(a-) rheumatoid arthritis patients.

Heteroclitic polyclonal and monoclonal anti-Gm(a) and anti-Gm(g) human rheumatoid factors react with epitopes induced in Gm(a-), Gm(g-) IgG by interaction with antigen or by nonspecific aggregation. A possible mechanism for the in vivo generation of rheumatoid factors.

Abstract Heteroclitic rheumatoid factors (RF) are specific for allotypic determinants, e.g., Gm(a) or Gm(g) on allogeneic, but not autologous IgG. All polyclonal RF we isolated from nine rheumatoid arthritis patients with circulating Gm(a-), (b+), (g-), (f+) IgG displayed dual heteroclitic activity for the Gm(a) and Gm(g) allotypes, as shown by using appropriate RBC agglutination assays and affinity columns bearing Gm(a+) or Gm(g+) IgG. To investigate possible mechanisms underlying the in vivo generation of heteroclitic RF, we tested the ability of nonspecifically and immune-specifically aggregated Gm(a-), (g-) IgG to function as targets for RF from Gm(a-), (g-) patients with rheumatoid arthritis. Heat aggregation (63 degrees C for 20 min) or binding to Ag (as in tetanus toxoid-antitetanus toxoid complexes) induced a "functional" Gm(a+) and/or (g+) phenotype in Gm(a-), (g-) IgG from five healthy subjects and five rheumatoid patients, as suggested by the ability of these altered IgG to function as efficient targets for six heteroclitic RF in direct binding and competitive inhibition experiments. That heterocliticity and dual Gm(a), Gm(g) specificity can be features of a single antibody molecule was formally demonstrated by analysis of a monoclonal RF (IgM mAb 61) generated from a Gm(a-), (g-) rheumatoid patient. RF mAb 61 displayed a high affinity (Kd, 10(-7) M) for IgG Fc fragment of Gm(a+) and (g+) IgG or aggregated autologous Gm(a-), (g-) IgG but did not bind to native autologous IgG. To investigate the molecular basis of the acquired Gm(a) phenotype, PBMC from five Gm(a-) patients with rheumatoid arthritis and two Gm(a-) normal subjects arthritis and two Gm(a-) normal subjects were cultured in vitro after activation with PWM. In most instances, these PBMC produced IgG that behaved as Gm(a+) in sensitive ELISA. Application of the polymerase chain reaction (PCR), using probes specific for the nucleotide sequence coding for the Gm(a) tetrapeptide, to the amplification of DNA from the in vitro-stimulated Gm(a-) normals or rheumatoid patients' PBMC provided no evidence for Gm(a) nucleotide sequences. The present data suggest that acquisition of the Gm(a) determinant by Gm(a-) IgG may result from subtle changes in the CH2-CH3 RF-binding region. Such changes would occur when Gm(a) IgG are complexed with Ag or nonspecifically altered, thereby providing a possible explanation for the induction of heteroclitic RF in Gm(a-) rheumatoid arthritis patients.

Molecular analysis of the V kappa III-J kappa junctional diversity of polyclonal rheumatoid factors during rheumatoid arthritis frequently reveals N addition.

Much interest was stirred in recent years by the evidence that rheumatoid factors (RF) variable regions are encoded by a restricted set of V genes, with little or no somatic mutations, that are often overexpressed in the fetal repertoire. This is reminiscent of what has been observed for natural autoantibodies. However, these data come from studies of monoclonal RF (mRF) isolated from patients with lymphoproliferative disorders who usually do not present autoimmune symptoms. The molecular characterization of RF during autoimmune diseases such as rheumatoid arthritis (RA) has been hampered for some time because of their polyclonality; recently using the polymerase chain reaction method, we have demonstrated that RF kappa variable regions from a patient with RA were encoded by V kappa III genes known to code for mRF but that these genes had undergone somatic mutations with a pattern suggesting an antigen-driven maturation. Because an important role of the light chain third complementarity-determining region (CDR3) in anti-IgG reactivity and idiotype expression has already been suspected for RF, we now report the molecular characterization of the junction regions of these rearranged V kappa gens. Surprisingly, our data show that in 55% of the cases there is addition of a proline and/or glycine amino acid residue at the recombination site between V kappa and J kappa. The sequence analysis of our patients' germ-line Vg and J kappa 4 genes segments and their flanking regions demonstrates that the additional codons are not readily explicable by recombination between germ-line sequences and probably result from an N addition process. Since we could not find such an additional codon in 15 previously published mRF kappa chains we suggest that "pathogenic" RF during RA and mRF derive from different, although overlapping, B cell subsets. Moreover, since additional codons at the recombination site of V kappa and J kappa seem exceptional in expressed human kappa chains and because the resulting amino acid residue is a proline in most cases, we think that RF kappa chain CDR3 is under a very strong selective pressure during RA.

A monoclonal anti-idiotype specific for human polyclonal IgM rheumatoid factor.

One of the hallmarks of rheumatoid arthritis (RA) is the production of high titers of rheumatoid factor (RF) antibody directed against the Fc portion of IgG. Anti-Id that recognize the majority of monoclonal RF from patients with B cell dyscrasias are reactive with only 1 to 2% of these polyclonal RF from RA patients. We describe a new monoclonal anti-Id, 4C9, that recognizes a L chain determinant on polyclonal IgM RF from patients with RA but does not recognize a panel of monoclonal RF from patients with B cell malignancies. 4C9 reactivity is found in the serum of 34/43 RF-positive RA patients and in 12/12 RF-positive synovial fluids, but in only 1/14 RF-negative sera from RA patients and 1/22 sera containing monoclonal IgM RF. 4C9 reactivity is highly enriched in purified IgM RF from nine RA patients and represents a variable percentage of total IgM RF up to a maximum of 23%. Furthermore, 4C9 reactivity is enriched in the synovial fluid of three of five RA patients compared with serum, suggesting that 4C9-reactive IgM RF are synthesized within the joint. IgG RF from RA synovial fluids are not 4C9 reactive, indicating either that different genes are used to encode IgM and IgG RF in RA patients, or that IgG RF have somatically mutated away from idiotypic reactivity.

Double reactivity of monoclonal and polyclonal rheumatoid factors for IgG and histones: Mapping of binding sites by means of histone synthetic peptides and anti-Id antibodies

Polyreactive antibodies able to bind various apparently unrelated structures represent a frequent antibody population in autoimmune diseases. In this work, the structural basis of the double reactivity of such autoantibodies was investigated using as models polyclonal and monoclonal human rheumatoid factors (RF) reacting with histones. Both direct ELISA binding and competitive inhibition experiments were performed. A more precise delineation of the histone regions recognized by the RFs was made by means of 27 synthetic peptides of these proteins. Anti-idiotope (Id) murine antibodies were used to map the binding sites involved on RF in the interaction with IgG and histones. Among the 13 polyclonal and six monoclonal RFs tested, four and two respectively were found to cross-react with IgG and histones. The fragments shown to be the most frequently recognized by RFs were located in residues 1-16 and 204-218 of H1, 1-20 and 65-85 of H2A, and 1-21 of H3. The results obtained by competitive ELISA assays using IgG, histone peptides and anti-Id monoclonal antibodies led us to confirm and characterize more precisely our previous finding suggesting the existence of topographically distinct binding sites for the different targets recognized by RFs.