IgA containing immune complexes in rheumatoid vasculitis and in active rheumatoid disease

Serum and synovial fluid (SF) from 68 patients with rheumatoid arthritis (RA) were studied for the presence of immune complexes (IC) and the results correlated with extraarticular features and/or disease activity. IC were measured by the 125I Clq binding assay (ClqBA) and with one detecting IgG, IgA, C3 or C4 in IC. Disease activity correlated significantly with IgG or IgA containing and Clq binding IC. The IgA containing IC were found only in 25% of the patients, including all but one case of rheumatoid vasculitis, but otherwise only in seropositive active RA. C3 and C4 IC did not correlated with disease activity, seropositivity or vasculitis. IC in serum did not correlate with SF levels, but C4 containing IC were more frequent in SF (60%) than in serum (30%). Thus serum IC did not reflect SF levels. Patients with vasculitis showed more IC in the sera than in SF.     

Immunological comparison of patients with rheumatoid arthritis with and without nephropathy.

Serum immunoglobulins IgG, IgA, and IgM, serum complement components C3 and C4, circulating immune complexes, antinuclear antibodies, and rheumatoid factor were measured in 56 patients with rheumatoid arthritis (RA) and nephropathy (23 with mesangial glomerulopathy; 13 with membranous glomerulonephritis; and 20 with amyloidosis) and 35 patients with RA without nephropathy (controls). Renal immunofluorescence findings in patients with mesangial glomerulopathy were compared with the serologic data. There were no differences in the occurrence of rheumatoid factor, antinuclear antibodies, and circulating immune complexes and the concentrations of serum complement C3 and C4 between various RA nephropathy groups and controls. Serum IgA and IgM concentrations were significantly higher in patients with mesangial glomerulopathy and amyloidosis than in controls. In patients with mesangial glomerulopathy glomerular IgM, IgA, and C3 were the most prominent findings in immunofluorescence examination. The serum IgA concentration was significantly higher in those patients with mesangial glomerulopathy with mesangial IgA deposits than in those without (4.97 (SD 1.03) g/l v 2.07 (1.21) g/l). The highest serum IgA concentrations (5.08 (1.39) g/l) were seen in the four patients with IgA glomerulonephritis. The prevalence of IgA glomerulonephritis in the renal biopsy material of the patients with RA was 5%, which possibly differs little from that seen in the general population. The results suggest that circulating immune complexes may not have any major role in the pathogenesis of various nephropathy types in patients with RA, contrary to their role in most extra-articular manifestations of RA.     

Relation of clinical activity of rheumatoid arthritis to immune complexes,complement components and anti-immunoglobulins

Summary Circulating immune complexes by fluid phase Clq binding assay, complement components and anti-immunoglobulin levels were studied in sera of 35 patients with rheumatoid arthritis (RA). In 23 of the 35 sera (65.7%), circulating immune complexes were positive, and the mean±SD of Clq binding activity (ClqBA), 44.5±19.4%, was significantly high compared to that of healthy persons, 17.4±8.2%. Antigenic determination of complement components revealed that Clq, C3, C5, C9, factor B and Cl esterase inhibitor (CIINH) were significantly high in sera of RA, but C4 and properdin were not. The disease activity correlated with ClqBA, IgG- and IgM-anti-immunoglobulins, C9 and serum IgG. On the other hand, ClqBA correlated with both IgG- and IgM-anti-immunoglobulin levels but not with complement components.     

Enhancement of Clq binding activity by IgM rheumatoid factor

Clq binding activity (ClqBA) averaged 18.1 +/- 14.5% (1 SD) in 28 rheumatoid arthritis (RA) sera (normal sera = 3.9 +/- 0.4%). Further analysis indicated that rheumatoid factor (RF) positive [RA (+)] sera averaged 30.4% ClqBA, significantly greater than the 3.9% ClqBA in RA RF negative [RA(-)] sera (p less than 0.01). In the RA(+) sera, RF titer correlated with ClqBA (r = +0.73). Addition of IgM RF to sera of normal, SLE, and RA(-) patients, as well as to aggregated IgG and reduced and alkylated aggregated IgG, resulted in significant increases in ClqBA, up to 14% in the latter group (p less than 0.01). Control IgM added to these same systems had no effect on ClqBA. IgM RF only slightly increased Clq binding of monomeric IgG.     

Circulating immune complexes and rheumatoid arthritis

Circulating immune complexes (CIC), as detected by the Clq binding assay (ClqBA) in sera from patients with rheumatoid arthritis (RA) were not demonstrable on analysis by ultracentrifugation on sucrose gradients. This discrepancy could be explained by the finding that polyethylene glycol 6000(PEG), used in the ClqBA to separate free radiolabelled Clq from complex bound Clq, increased the avidity of rheumatoid factor (RF), resulting in the formation of Clq binding RF IgM IgG complexes. Addition of purified RF IgM to normal human serum generated a positive ClqBA in a dose dependent way. The increased complex formation between RF IgM and IgG by PEG was also demonstrated in an enzyme linked immunoabsorbent assay and with sucrose gradients, where complexes became detectable when PEG was present. On the other hand RF IgM IgG Clq complexes obtained from the ClqBA dissociated upon removal of PEG. We conclude that high amounts of immune complexes, detected in RA sera by the ClqBA, are at least partly the result of in vitro complex formation between RF IgM and IgG. Therefore the results of this assay do not reflect the situation in the circulation in vivo.     

Rheumatoid factor isotypes and circulating immune complexes in rheumatoid arthritis

Solid phase enzyme immunoassays were here used to quantify rheumatoid factors (RF) of the IgM, IgG and IgA classes and the immune complexes (IK) by their ability to bind to C1q or conglutinin in both the serum and synovial fluid of patients with rheumatoid arthritis (RA). Elevated serum levels of any RF isotype could be found in all patients with seropositive RA (IgM: 63%, IgG: 87%, IgA: 90%). Seronegative patients with RA presented to a significantly lesser extent with elevated levels of all the RF isotypes tested (IgM: 0%, IgG: 40%, IgA: 32%). Synovial fluid RF levels were significantly higher in SPRA patients than in SNRA patients with the exception of IgG-RF. All of the RF classes in both RA groups, however, were elevated when compared to RF in the synovial fluid of patients with osteoarthrosis. Both C1q binding and conglutinin binding immune complexes were significantly higher in the synovial fluid than in the serum of RA patients. The erythrocyte sedimentation rate and plasma iron levels were correlated with the levels of C1q binding immune complexes (IC) in the synovial fluid; total iron binding capacity showed an inverse relationship to synovial fluid IgG-RF levels. A radiographic index was also correlated with IgG-RF levels in the synovial fluid. Extraarticular manifestations were significantly more frequent in patients with elevated serum levels of IgM-RF or conglutinin binding IC. These findings indicate that IgG-RF in the synovial fluid and the formation of IC determined by their ability to bind C1q seem to be closely related to clinical features of local disease.(ABSTRACT TRUNCATED AT 250 WORDS)     

Increased arteriovenous carboxyhemoglobin differences in patients with inflammatory pulmonary diseases

PURPOSE: Exhaled carbon monoxide and arterial blood carboxyhemoglobin concentrations increase in inflammatory pulmonary diseases. The present study was undertaken to elucidate whether arteriovenous carboxyhemoglobin (a-vHb-CO) concentration differences are also useful to define the site of inflammation, either in the lung or organs other than the lung. MATERIALS AND METHODS: We examined concentrations of carboxyhemoglobin in both arterial and peripheral venous blood and exhaled carbon monoxide in patients with acute pulmonary inflammation including bronchial asthma (n = 18) and pneumonia (n = 33), and those in patients with extrapulmonary inflammatory diseases, including acute pyelonephritis (n = 28) and active rheumatoid arthritis (n = 16). RESULTS: The values of carboxyhemoglobin in both arterial and peripheral venous blood were significantly higher in patients with pulmonary and extrapulmonary inflammation compared with those in control subjects (n = 22). Furthermore, a-vHb-CO differences in patients with inflammatory pulmonary diseases were higher than those in patients with acute pyelonephritis and patients with rheumatoid arthritis, and than those in control subjects. The a-vHb-CO differences correlated with the WBC count of peripheral venous blood in patients with pneumonia. In patients with bronchial asthma, the a-vHb-CO differences inversely correlated with FEV(1), although they did not correlate with WBC count of peripheral venous blood. The a-vHb-CO differences in patients with acute pyelonephritis were higher than those in patients with active rheumatoid arthritis. CONCLUSION: The present study suggests that a-vHb-CO differences may be a useful means to define the site of inflammation, either in the lung or organs other than the lung, in patients with a fever of unknown origin. The large a-vHb-CO differences may be caused by carbon monoxide production in pulmonary inflammation.     

Class-specific rheumatoid factors, DR antigens, and amyloidosis in patients with rheumatoid arthritis.

Class-specific rheumatoid factors (RFs) were measured by enzyme immunoassay in 59 patients with rheumatoid arthritis complicated by systemic amyloidosis (RA+A), 47 patients with rheumatoid arthritis without amyloid (RA), 106 patients with other rheumatic diseases (juvenile rheumatoid arthritis, systemic lupus erythematosus, Sjögren''s syndrome), and 55 blood donors. The patients with RA+A were characterised by a high prevalence of RF negativity; the IgM RF concentration was raised in only 18 of the 59 patients (31%, p less than 0.001 v RA), the IgG RF concentration in 20 of 59 (34%, p less than 0.001 v RA), and the IgA RF concentration in 24 of 59 (41%, p less than 0.001 v RA). A higher prevalence of HLA-DR4 (p less than 0.001) and a lower prevalence of DR2 (p less than 0.05) were found among 48 tested patients with RA+A when compared with a control panel consisting of 500 blood donors. No significant differences in the prevalence of DR1-DR7 or B27 antigens were observed, however, between patients with RA with or without amyloid.     

Abnormal plasma fibrinolysis in patients with rheumatoid arthritis and impaired endothelial fibrinolytic response in those complicated by vasculitis.

OBJECTIVES--(a) To assess plasma fibrinolytic parameters in patients with rheumatoid arthritis (RA) and to determine whether there are differences between patients with RA alone and those with RA complicated by vasculitis. (b) To determine if patients with RA respond differently to venous occlusion compared with normal subjects and to assess whether such a response differs in patients with RA alone and those with rheumatoid vasculitis. (c) To determine the extent of vascular damage in patients with rheumatoid vasculitis and if this correlates with the levels of plasma fibrinolytic parameters. METHODS--Sixty three patients with RA (38 had RA only and 25 had evidence of rheumatoid vasculitis) were recruited. Plasma levels of tissue plasminogen activator antigen (t-PA Ag), plasminogen activator inhibitor (PAI) activity, and factor VIII von Willebrand factor (vWF) were measured before and 10 minutes after venous occlusion. RESULTS--Patients with RA, with or without rheumatoid vasculitis, had higher baseline PAI levels than control subjects. The difference was statistically significant for patients with RA alone but was not statistically significant for patients with rheumatoid vasculitis. After venous occlusion, t-PA Ag levels increased significantly in normal subjects and patients with RA alone, but not in patients with rheumatoid vasculitis. Plasma levels of vWF were significantly higher in patients with rheumatoid vasculitis than in normal subjects and those with RA alone. In patients with RA alone, baseline vWF correlated positively with t-PA Ag levels, whereas a negative correlation was found between these two parameters in patients with rheumatoid vasculitis. A negative correlation between vWF and t-PA Ag levels after venous occlusion was also found in patients with rheumatoid vasculitis. CONCLUSIONS--Patients with rheumatoid vasculitis showed evidence of vascular damage with increased levels of vWF and impaired t-PA Ag release after venous occlusion, a useful measurement of endothelial reserve to remove fibrin. This may be of pathophysiological importance in the development of vasculitis in these patients.     

Serum immune complexes containing IgA appear to predict erosive arthritis in a longitudinal study in rheumatoid arthritis.

Fifty seven patients with rheumatoid arthritis (RA) were studied longitudinally, and the presence of rheumatoid factor (RF) and various types of immune complexes (IC) was correlated with joint activity and the presence of extra-articular features (EAF). In a cross sectional study it was found that the levels of circulating IC and RF correlated significantly with joint disease activity and the presence of EAF. Longitudinally, levels of IC measured by the C1q binding activity and IC containing IgG and IgM correlated significantly with fluctuations in joint disease activity, whereas IC containing IgG and IgA correlated with the occurrence of EAF. RF and IC levels, however, did not predict the clinical course of the disease. IC containing C3 and C4 were found infrequently and were only present in patients with active rheumatoid vasculitis (RV). The continuous presence of these IC appeared to be linked to the recurrence of vasculitis, irrespective of treatment. Significantly more erosions of hands and feet were found after one year follow up in those RA patients who presented early (disease duration less than one year) who initially had a raised serum IgA IC level (r = 0.72; p less than 0.005).     

Comparative study of different enzyme immunoassays for measurement of IgM and IgA rheumatoid factors

OBJECTIVE: To compare the value of various IgM and IgA rheumatoid factor (RF) tests for the diagnosis of rheumatoid arthritis (RA). METHODS: Firstly, the latex test, one global assay (for IgM, IgA, and IgG RF), six IgM, and four IgA RF assays were compared in a particularly challenging situation-that is, with 67 patients with RA, many of whom were latex negative, and 91 non-RA controls, many of whom were latex positive. More detailed evaluation followed with three IgM RF tests (two commercially available kits and one assay developed in our laboratory) and two IgA RF tests (one commercially available and one from our laboratory) in two more representative samples of rheumatological patients (146 RA and 75 non-RA controls). RESULTS: Diagnostic performance differed considerably between the assays. For IgM RF detection the highest sensitivity (88%) was obtained with the Diamedix kit (specificity 67%) and for IgA RF with the Inova kit (sensitivity 65%, specificity 88%). Combining one IgM and one IgA RF test improved diagnostic performance when both tests were in agreement, but at the cost of yielding 15-27% of discrepant results which did not help in ruling RA in or out. Mean concentration values differed significantly among IgM RF tests, and in most cases concentrations were not correlated. CONCLUSIONS: Available tests for IgM RF isotype vary in accuracy, and none is uniformly better than all the others. For IgA RF isotype, the Inova kit appears to be the best. Quantitative results cannot be compared across tests. Combination of one IgM and one IgA RF test may improve diagnostic accuracy.     

Immunopathological abnormalities in the normal skin of patients with rheumatoid arthritis in relation to clinical and serological findings: a one year follow up study.

Fifty two patients with seropositive rheumatoid arthritis (RA) were studied over a period of one year to investigate possible relationships among changes of circulating immune complexes (CIC), deposits of immunoglobulins and complement around the cutaneous blood vessels, clinical activity of the disease, and the presence of extra-articular manifestations (EAM). The presence or absence of IgM and C3 in and around the cutaneous blood vessels correlated significantly with the presence or absence of extra-articular features in cross sectional and longitudinal studies. Patients with evidence of these cutaneous immune deposits also had a greater prevalence of CIC as determined by the Clq binding assay (ClqBA) or polyethylene glycol (PEG) assay for IC containing IgM (IgM IC). Although the degree of perivascular mononuclear cell infiltration around the blood vessels in the papillary dermis was related to the patients' clinical state at the initial assessment, it did not correlate with the later changes in the activity of the joint disease or the occurrence of EAM. Thus the deposition of immunoglobulin or complement, or both, seems to be independent of cellular infiltration. The meaning of these cellular infiltrates is not yet fully understood. Our study has shown that many patients with RA who appeared to have only joint disease in fact had subclinical systemic disease as reflected by a positive skin biopsy or CIC. Moreover, the disappearance of IgM deposits from the skin correlated with the disappearance of EAM and improvement of joint disease.     

Raised serum IgG and IgA antibodies to mycobacterial antigens in rheumatoid arthritis.

Autoantigens cross reactive with mycobacteria are implicated in the pathogenesis of adjuvant arthritis in the rat, and there are reports of changes in the immune response to mycobacteria in human rheumatoid arthritis (RA). We have therefore examined the IgM, IgG, and IgA antibody levels to crude mycobacterial antigens and to two recombinant mycobacterial heat shock/stress proteins (65 kD and 71 kD) in sera from patients with RA, systemic lupus erythematosus (SLE), and Crohn's disease, and from healthy controls. IgA binding to the crude mycobacterial antigens was significantly raised in RA sera, though IgG and IgM binding tended to be lower than in controls. Both IgA and IgG binding to the heat shock proteins were significantly raised in the RA sera. Smaller significant rises in both classes were seen in sera from patients with SLE, and in the IgA class only to the 65 kD protein in Crohn's disease. The rises in IgG and IgA antibodies to the 65 kD protein in RA were significantly higher than in the other diseases, however. It is interesting that this protein is the one responsible for adjuvant arthritis in the rat.     

Determination of IgA- and IgM-rheumatoid factors in patients with rheumatoid arthritis with and without nephropathy.

OBJECTIVE: To clarify the characteristics and pathogenesis of renal disorders in patients with rheumatoid arthritis (RA). METHODS: In this study, 143 patients with RA were included, from whom 43 with urinary abnormalities were biopsied. Serum rheumatoid factor (RF) concentrations of IgA and IgM isotypes were also measured in these patients by enzyme linked immunosorbent assay. RESULTS: Light microscopy of renal biopsy specimens showed minor glomerular abnormalities in six patients, mesangial proliferative glomerulonephritis (GN) in 21, membranous nephropathy in seven, renal amyloidosis in seven, and tubulointerstitial nephritis in two. Twelve patients with mesangial proliferative GN and one with minor glomerular abnormalities were found by immunofluorescence microscopy to have abnormalities consistent with IgA GN. Although the concentrations of IgA-RF in patients with IgA GN were slightly raised compared with those with glomerulopathy established by biopsy but not associated with IgA GN, the concentrations of IgA-RF were higher in patients with RA with vasculitis or interstitial pneumonia than those with RA complicated by IgA GN. CONCLUSIONS: Mesangial proliferative GN, including IgA GN, may be a frequent renal lesion in Japanese patients with RA. IgA-RF may play little pathogenetic part in the development of IgA GN in RA.     

Lymphocyte infiltration and the synthesis of IgM and IgA rheumatoid factors by rheumatoid synovial membrane

Summary IgM and IgA rheumatoid factor (RF) synthesis by synovial membrane mononuclear cells was measured in 14 patients with rheumatoid arthritis (RA). The results were compared with blood mononuclear cell cultures and correlated with the intensity of lymphocyte infiltration of the synovium. IgM RF was produced by all synovial cultures compared with 56% of blood cultures; IgA RF was produced by 86% of synovial cultures and by 21% of blood cultures. A correlation was observed between synovial IgM RF synthesis, but not IgA RF synthesis, and the intensity of T cell and B cell infiltration of the synovial membrane.     

Anti-saccharomyces cerevisiae IgA antibodies are raised in ankylosing spondylitis and undifferentiated spondyloarthropathy

OBJECTIVES: To investigate whether anti-Saccharomyces cerevisiae antibodies (ASCA), a marker for Crohn's disease (CD), are present in spondyloarthropathies (SpA) and in the subgroups ankylosing spondylitis (AS), undifferentiated SpA (uSpA), and psoriatic arthritis (PsA), in comparison with healthy and inflammatory controls (patients with rheumatoid arthritis (RA)). METHODS: ASCA IgA and IgG levels were measured with an enzyme linked immunosorbent assay (ELISA) kit (Medipan, Germany) in 26 patients with CD, 108 patients with SpA (43 patients with AS, 20 patients with uSpA, 45 patients with PsA), 56 patients with RA and 45 healthy controls. Gut biopsy samples were available in 18 AS and 10 patients with uSpA, these samples were screened for the presence of inflammation. RESULTS: Both ASCA IgG and IgA levels were raised in CD compared with healthy controls and patients with RA. ASCA IgA, but not IgG levels, were higher in SpA than in both healthy and RA controls. ASCA IgA levels were raised in AS and uSpA, but not in PsA. No significant differences in ASCA IgA levels were noted between patients with SpA with and without histological gut inflammation. CONCLUSION: ASCA IgA levels are significantly higher in SpA, and more specifically in AS, than in healthy controls and patients with RA. This is the first serum marker associated with SpA. No correlation between the presence of subclinical bowel inflammation and ASCA IgA levels was noted. However, it remains to be evaluated whether patients with SpA with ASCA have an increased risk of developing CD.     

Elevated levels of IgM and IgA antibodies to Proteus mirabilis and IgM antibodies to Escherichia coli are associated with early rheumatoid factor (RF)-positive rheumatoid arthritis

OBJECTIVE: Antibodies to Proteus mirabilis were previously detected in patients with established rheumatoid arthritis (RA). We examined the prevalence of antibodies to P. mirabilis and their associations with RA in early synovitis patients. METHODS: Two hundred and forty-six patients with inflammatory arthritis for less than 1 yr were prospectively evaluated for 1 yr. Of these patients, 30% had rheumatoid factor (RF)-positive RA, 16% RF-negative RA, 17% a spondyloarthropathy and 37% undifferentiated arthritis. Serum antibodies to P. mirabilis, Escherichia coli and other potentially arthritogenic organisms (Chlamydia, Salmonella, Shigella, Campylobacter, Yersinia and parvovirus B19) and for antibodies specific for immunoglobulin (Ig) G damaged with advanced glycation end-products (anti-IgG-AGE) were measured. RESULTS: IgM and IgA anti-Proteus antibodies were significantly higher in patients with RF-positive RA compared with all other patient groups (P < 0.0005 and P < 0.005). Anti-P. mirabilis IgG, and IgG, IgA, and IgM antibodies to other potentially arthritogenic pathogens did not differ in the patient groups. IgM antibodies to E. coli were elevated in RF-positive RA patients. Anti-P. mirabilis IgM and IgA results were not explained by false-positive reactions, because after absorption of RF there was no decrease in antibodies to Proteus in 10 of 12 patients. Proteus and E. coli antibodies were highest in patients positive for both RF and anti-IgG-AGE antibodies (P<0.001). Patients with erosions tended to have higher IgA anti-Proteus titres, but no association with the shared HLA epitope or treatment was detected. CONCLUSION: Anti-P. mirabilis IgM and IgA and anti-E. coli IgM antibody elevations are associated with early seropositive RA and the presence of anti-IgG-AGE antibodies. The role that P. mirabilis or E. coli plays in early RF-positive RA requires further investigation.     

A comparative study of IgG second- and third-generation anti-cyclic citrullinated peptide (CCP) ELISAs and their combination with IgA third-generation CCP ELISA for the diagnosis of rheumatoid arthritis

To compare IgG anti-cyclic citrullinated peptide (CCP) enzyme-linked immunosorbent assays (ELISAs) of second (anti-CCP2) and third generations (anti-CCP3) for the diagnosis of rheumatoid arthritis (RA), an IgA CCP3 ELISA was also evaluated. Combinations of the use of the three tests were evaluated. Anti-CCP2 IgG, anti-CCP3 IgG, and anti-CCP3 IgA antibody levels were determined by ELISAs in the serum of 70 patients with rheumatoid arthritis, 34 patients with systemic lupus erythematosus (SLE), and 54 normal subjects. We evaluated the serum levels, diagnostic performance, and the use of a combination of tests for RA diagnosis. Statistical analyses include receiver operating curves (ROCs) and others. The serum levels were higher in RA patients. Sensitivity, specificity, positive predictive value, negative predictive value, positive likelihood ratio (LR), and negative LR were, respectively, 78.6%, 94.3%, 91.7%, 84.7%, 13.8, and 0.23 for anti- CCP2 IgG and 82.9%, 93.2%, 90.6%, 87.2%, 12.2, and 0.18 for anti-CCP3 IgG. These values were better than the same statistical tests for anti-CCP3 IgA. ROC analysis showed that anti-CCP2 IgG and anti-CCP3 IgG had good performance and similar areas. Measuring both IgG and IgA anti-CCP tests increases the specificity if both tests were positive and increases the sensitivity if either test were positive. In our population, anti-CCP2 IgG and anti-CCP3 IgG had good diagnostic performance. Anti-CCP3 IgG had 4.3% more sensitivity than the anti-CCP2 IgG test while sustaining high specificity. This and other studies suggest the development of a dual test—CCP3 IgG and IgA that may be a potential diagnostic tool.     

Can we predict thrombotic tendency in rheumatoid arthritis? A thromboelastographic analysis (with ROTEM)

Clinical Rheumatology - The higher incidence of arterial and venous events is well established in patients with rheumatoid arthritis (RA). Our aim here was to investigate whether there is a...     

Isotypes of rheumatoid factors in rheumatoid arthritis and chronic liver diseases

We studied isotype-specific rheumatoid factors (RFs) to clarify their significance in rheumatoid arthritis (RA) and to verify the difference in RF isotypes between RA and chronic liver diseases (CLD). Isotype-specific RFs in RA and in CLD were measured by enzyme-linked immunosorbent assay (ELISA). Most sera (n = 51, 94.1%) from RA patients contained some kind of RF isotypes (92.1% for IgM RF, 76.4% for IgG RF, and 43.1% for IgA RF), and seronegative RA by ELISA was seen in only 11.8% (n = 6). The most characteristic combination of RF isotypes in active RA was IgG, IgA, and IgM. This combination of RF isotypes changed to IgG plus IgM, according to the diminution of RA activity; then, we found only IgM RF in inactive RA. The titers of each RF isotype also decreased in parallel with the activity of RA. IgA RF seemed to be the most sensitive factor for evaluating the activity of RA. In CLD, almost the same high frequency (n = 49, 89.8% for IgM RF, 59.2% for IgG RF), with the same titer levels seen in RA, was observed. On the other hand, IgA RF was significantly lower in frequency (n = 9, 18.4%) and in titer, compared with the finding in RA. Surprisingly, even in CLD, true seronegativity by ELISA was also found in very few patients (n = 4, 8.1%). In CLD, positive RFs detected by agglutination assay were seen more often in chronic hepatitis than in liver cirrhosis. In RA patients, significant associations of IgA RF and the serum concentration of IgA, and IgG RF and the serum concentration of IgG, were observed. On the other hand, in CLD patients, significant associations of IgG RF and the serum IgG concentration, and of IgM RF and the serum IgM concentration, were observed. These results indicated that IgA RF in active RA is the most characteristic RF isotype distinguishing it from other nonrheumatic diseases, as well as from inactive RA. RF isotypes reflected the background polyclonal B-cell activation in different manners in both diseases. In CLD, RF isotypes seemed to be disease-related immunological disorders reflecting disease progression. Received: February 17, 2000 / Accepted: July 5, 2001