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Objective: To study the adherence of rheumatologists to the Dutch guidelines for anti-tumour necrosis factor alpha (TNF-alpha) treatment. The secondary objective was to evaluate alternatives to the present guidelines with regard to the percentage of responders and costs., Methods: The response (>1.2 DAS28 decrease) in patients who started on anti-TNF-alpha treatment for the first time was evaluated at 3 and 6 months after initiation. How many patients continued or discontinued their initial anti-TNF-alpha treatment was evaluated. Possible alternative guidelines were evaluated by means of a decision tree, with regard to the expected percentage of successfully (responders) and unsuccessfully treated patients and expected costs., Results: At 3 months 56% (N = 306) and 44% (N = 233) of all 539 evaluable patients were classified as responders or non-responders, respectively. Despite the guidelines, most (81%) (N = 189) of the non-responders continued treatment. 37% of the non-responders who continued anti-TNF-alpha treatment were eventually classified as responders at 6 months. Decision analytical modelling showed that with equal expected costs all alternative strategies would result in more responders than according to theoretical full adherence with the guidelines. "Continuation in case of partial response" had the best trade-off between successfully treated patients (64%) and unsuccessfully treated patients (17%)., Conclusion: There was suboptimal adherence to the Dutch guidelines for treatment with anti-TNF-alpha for rheumatoid arthritis patients. This seemed to be justified by the fact that a delayed response up to 6 months was shown. If treatment is continued despite a non-response at 3 months, this is only recommended in patients with at least a partial response (at least 0.6 DAS28 improvement).

Aim: to evaluate the effects of adalimumab, etanercept and infliximab on disease activity, functional ability and quality of life and the medication costs in a naturalistic design., Methods: All patients from the Dutch Rheumatoid Arthritis Monitoring (DREAM) register starting on tumour necrosis factor (TNF)alpha-blocking agents for the first time were monitored and assessed by trained research nurses every 3 months. The primary outcome was the Disease Activity Score (DAS28) course over the 12 months follow-up, analysed by linear mixed models. Secondary outcomes were the Health Assessment Questionnaire (HAQ), EuroQol five dimensions (EQ-5D) and the Short-Form 36 items (SF36) scores, and medication-related total costs., Results: The DAS28 and SF-36 physical component scale decreased in all three medication groups over 12 months, but the decrease was larger for adalimumab and etanercept in comparison to infliximab (p<0.001). The analyses of the HAQ and the EQ-5D scores showed the same (non-significant) trend, namely that at 12 months, the functionality and quality of life was better for adalimumab and etanercept patients. With regard to the medication costs, infliximab treatment resulted in significantly higher costs over the follow-up period than treatments with either adalimumab or etanercept. The comparison between adalimumab and etanercept showed a significant difference in the 12-month DAS28 course (p = 0.031). There were no additional indications for differences in effectiveness or costs between adalimumab and etanercept., Conclusion: The evaluation of the effectiveness and costs showed that adalimumab and etanercept are more or less equal and favourable compared to infliximab in the first year of treatment.

Objective: To assess the effect of a functional polymorphism (676T>G, M196R) in the tumour necrosis factor receptor super family 1b (TNFSF1b) gene on disease activity, radiological joint damage and response to infliximab and adalimumab treatment in patients with rheumatoid arthritis (RA)., Methods: Two cohorts of patients with RA were genotyped for the 676T>G polymorphism (rs1061622) in exon 6 of the TNFSF1b gene by restriction fragment length polymorphism analysis. One cohort (n = 234) included patients from the Dutch Rheumatoid Arthritis Monitoring register with detailed information on their response to anti-TNF therapy (infliximab and adalimumab), the other cohort comprised patients from a long-term observational early inception cohort at our centre (n = 248)., Results: The 676T>G polymorphism was not associated with anti-TNF response after 3 or 6 months of treatment. Linear regression analysis showed no significant difference in the progression of radiological joint damage during the first 3 and 6 years of disease between the three genotype groups (TT, TG and GG). Additionally, no difference in mean disease activity between genotypes was seen after 3 and 6 years of disease., Conclusion: Despite its demonstrated functionality, the 676T>G polymorphism in the TNFSF1b gene does not have a major role in either the response to anti-TNF therapy or in the disease severity or radiological progression in RA.

Background: Randomised controlled trials (RCTs) evaluating the efficacy of antagonists to tumour necrosis factor alpha (TNFalpha) showed high response percentages in the groups treated with active drugs., Objective: To compare the efficacy of anti-TNF treatments for rheumatoid arthritis (RA) patients in RCTs and in daily clinical practice, with an emphasis on the efficacy for patients eligible and not eligible for RCTs of anti-TNF treatments., Methods: First, randomised placebo-controlled trials written in English for etanercept, infliximab and adalimumab for patients with RA were selected by a systematic review. Second, the DREAM (Dutch Rheumatoid Arthritis Monitoring) register with patients starting for the first time on one of the TNF-blocking agents was used. Patient characteristics, doses of medication and co-medication as well as the ACR20 response percentages were compared between RCTs and DREAM data, stratified for trial eligibility., Results: In 10 of 11 comparisons, the ACR20 response percentages were lower in daily clinical practice than in the RCT active drug group, which was significant in five of 11 comparisons. Only 34-79% of DREAM patients fulfilled the selection criteria for disease activity in the several RCTs examined. DREAM patients eligible for RCTs had higher response percentages than ineligible DREAM patients. ACR20 response percentages of eligible DREAM patients were comparable with the ACR20 response percentages of the RCT active drug group in 10 of 11 comparisons., Conclusion: The efficacy of TNF-blocking agents in RCTs exceeded the efficacy of these drugs in clinical practice. However, in clinical practice more patients with lower disease activity were treated with TNF-blocking agents compared with those treated in RCTs. For daily practice patients who were eligible for RCTs, responses were more similar to responses reached in RCTs.

Modifications occurring on autoantigens during cell death have been proposed to have a role in the initiation of autoimmune diseases. Patients suffering from mixed connective tissue disease (MCTD) produce autoantibodies directed to U1 small nuclear ribonucleoprotein (snRNP), and antibodies against a 70 kDa protein component, the U1-70K (70K) protein, are the most prominent. During apoptosis, 70K is cleaved by caspase-3 to a 40 kDa product, which remains associated with the complex. Autoantibodies preferentially recognizing the apoptotic form of 70K have been described previously, and an apoptosis-specific epitope on 70K has been identified. This study shows that 29 of 53 (54%) MCTD sera preferentially recognize the apoptotic form of 70K over intact 70K. Moreover, we show that antibodies directed to an apoptosis-specific epitope on 70K are more specifically associated with MCTD than other anti-70K antibodies, suggesting that apoptotic 70K is a better antigen for the detection of these antibodies in MCTD patients. Longitudinal analysis of 12 MCTD patients showed in several patients that early sera are relatively enriched with antibodies recognizing an apoptosis-specific epitope, and that the levels of these apoptosis-specific antibodies decrease in time. These findings indicate that the early detection of apoptotic 70K is of considerable interest for anti-U1 snRNP-positive patients.

Objective: To determine if participation of the spouse of patients with rheumatoid arthritis in cognitive-behavioral oriented self-management training aimed at improving disease related cognitions and coping with pain has additional benefits for the patients., Methods: A total of 59 couples were randomly assigned to 2 conditions. In the experimental condition the couples participated in a group program aimed at restructuring disease related cognitions and decreasing passive coping. In the control condition, only the patient participated. Disease status, self-reported physical and psychological functioning, coping, disease related cognitions, and marriage characteristics were assessed prior to the intervention and 2 weeks and 6 months postintervention. A general linear model with repeated measures was used to test for differences between conditions., Results: In both conditions, similar positive changes in disease activity, cognitions, coping, and physical and psychological functioning were observed. Patients reported a decrease in potential support. There were no differences between conditions. However, at the followup assessment patients in the experimental condition reported more improvement of disease related communication with their spouse., Conclusion: No evidence was found for additional beneficial effects of spouse participation in the cognitive-behavioral oriented self-management group treatment.

Background: Antibodies directed to proteins containing the non-standard amino acid citrulline, are extremely specific for rheumatoid arthritis (RA). Peptidylcitrulline can be generated by post-translational conversion of arginine residues. This process, citrullination, is catalysed by a group of calcium dependent peptidylarginine deiminase (PAD) enzymes., Objective: To investigate the expression and activity of four isotypes of PAD in peripheral blood and synovial fluid cells of patients with RA., Results: The data presented here show that citrullination of proteins by PAD enzymes is a process regulated at three levels: transcription-in peripheral blood PAD2 and PAD4 mRNAs are expressed predominantly in monocytes; PAD4 mRNA is not detectable in macrophages, translation-translation of PAD2 mRNA is subject to differentiation stage-specific regulation by its 3' UTR, and activation-the PAD proteins are only activated when sufficient Ca(2+) is available. Such high Ca(2+) concentrations are normally not present in living cells. In macrophages, which are abundant in the inflamed RA synovium, vimentin is specifically citrullinated after Ca(2+) influx., Conclusion: PAD2 and PAD4 are the most likely candidate PAD isotypes for the citrullination of synovial proteins in RA. Our results indicate that citrullinated vimentin is a candidate autoantigen in RA.

This study sets out to determine predictors of marital and sexual satisfaction in patients with rheumatoid arthritis (RA) and their spouses. Fifty-nine patients and their spouses completed questionnaires independent from each other. Multiple correlations with marital and sexual satisfaction were computed for demographic variables, disease status, psychological distress, and social support. The results indicate that psychological distress and social support are more important than objectively assessed disease status in determining marital and sexual satisfaction in patients with RA.

Sera from patients suffering from systemic autoimmune diseases such as systemic lupus erythematosus (SLE) and systemic sclerosis (SSc) have been shown to contain reactivities to nuclear components. Autoantibodies specifically targeting nucleolar antigens are found most frequently in patients suffering from SSc or SSc overlap syndromes. We determined the prevalence and clinical significance of autoantibodies directed to nucleolar RNA-protein complexes, the so-called small nucleolar ribonucleoprotein complexes (snoRNPs). A total of 172 patient sera with antinucleolar antibodies were analysed by immunoprecipitation. From 100 of these patients clinical information was obtained by chart review. Autoantibodies directed to snoRNPs were detected not only in patients suffering from SSc and primary Raynaud's phenomenon (RP), but also in patients suffering from SLE, rheumatoid arthritis (RA) and myositis (PM/DM). Antibodies against box C/D small snoRNPs can be subdivided in antifibrillarin positive and antifibrillarin negative reactivity. Antifibrillarin-positive patient sera were associated with a poor prognosis in comparison with antifibrillarin negative (reactivity with U3 or U8 snoRNP only) patient sera. Anti-Th/To autoantibodies were associated with SSc, primary RP and SLE and were found predominantly in patients suffering from decreased co-diffusion and oesophagus motility and xerophthalmia. For the first time autoantibodies that recognize box H/ACA snoRNPs are described, identifying this class of snoRNPs as a novel autoantigenic activity. Taken together, our data show that antinucleolar patient sera directed to small nucleolar ribonucleoprotein complexes are found frequently in other diseases than SSc and that categorization of diagnoses and clinical manifestations based on autoantibody profiles seems particularly informative in patient sera recognizing box C/D snoRNPs.

Objective: To study the effect of folates on discontinuation of methotrexate (MTX) as single-drug antirheumatic treatment due to toxicity, to determine which type of adverse events are reduced, to study the effects on the efficacy of MTX, and to compare folic with folinic acid supplementation in a 48-week, randomized, double-blind, placebo-controlled trial., Methods: Patients with active RA (n = 434) were randomly assigned to receive MTX plus either placebo, folic acid (1 mg/day), or folinic acid (2.5 mg/week). The initial MTX dosage was 7.5 mg/week; dosage increases were allowed up to a maximum of 25 mg/week for insufficient responses. Folate dosages were doubled once the dosage of MTX reached 15 mg/week. The primary end point was MTX withdrawal because of adverse events. Secondary end points were the MTX dosage and parameters of efficacy and toxicity of MTX., Results: Toxicity-related discontinuation of MTX occurred in 38% of the placebo group, 17% of the folic acid group, and 12% of the folinic acid group. These between-group differences were explained by a decreased incidence of elevated liver enzyme levels in the folate supplementation groups. No between-group differences were found in the frequency of other adverse events or in the duration of adverse events. Parameters of disease activity improved equally in all groups. Mean dosages of MTX at the end of the study were lower in the placebo group (14.5 mg/week) than in the folic and folinic acid groups (18.0 and 16.4 mg/week, respectively)., Conclusion: Both folate supplementation regimens reduced the incidence of elevated liver enzyme levels during MTX therapy, and as a consequence, MTX was discontinued less frequently in these patients. Folates seem to have no effect on the incidence, severity, and duration of other adverse events, including gastrointestinal and mucosal side effects. Slightly higher dosages of MTX were prescribed to obtain similar improvement in disease activity in the folate supplementation groups.

The records of 46 patients with anti-(U1)snRNP antibodies and a minimal period of follow-up after first clinical presentation of at least 5 yr were examined with emphasis on symptoms contributing to established criteria of SLE, systemic sclerosis (SSc), RA or dermato- or polymyositis (DM/PM). At first clinical presentation 13 (28%) of the 46 patients studied fulfilled ARA-criteria for SLE (n = 10), RA (n = 2) and SSc (n = 1), and 33 (72%) were classified as mixed connective tissue disease (MCTD). During follow-up 18 patients initially classified as MCTD were now classified as SLE (n = 5), SSc (n = 7), RA (n = 3), or a combination of these disorders (n = 3). A transformation of MCTD towards these connective tissue diseases occurred 2.6 +/- 3 yr (mean +/- S.D.) after first clinical presentation. At the end of the follow-up period 67% of the patients fulfilled ARA criteria for SLE, SSc, RA or a combination of these diseases. The majority of patients with anti-(U1)snRNP antibodies have or will develop a classified connective tissue disease within 5 yr after clinical presentation. This undermines the concept of MCTD being a distinct clinical entity.

To compare efficacy, toxicity, and the pharmacokinetics of the combination of sulphasalazine (SASP) and methotrexate (MTX) vs MTX alone in the treatment of SASP-resistant RA we conducted a controlled open clinical trial. Forty RA patients with active arthritis despite adequate SASP therapy, were allocated randomly to regimes of either SASP+MTX or MTX alone. The patients were evaluated openly by a single observer for 24 weeks. In the first 15 patients using the combination, pharmacokinetics of MTX without and with SASP were studied. Thirty-eight patients completed the trial. The mean decrease in the disease activity score in the group of patients receiving the combination was significantly greater than in the MTX group (-2.6 vs -1.3 respectively). The same pattern was seen concerning the other efficacy variables. There was no difference in the occurrence of toxicity. SASP had no influence on the pharmacokinetics of MTX. In conclusion in this open study the efficacy of the combination of MTX and SASP seems to be superior to MTX alone, the toxicity of both therapies was similar. This effect was not explained by the pharmacokinetics of MTX which were not altered by concomitant SASP administration.

To establish the symptoms and clinical course of juvenile-onset mixed connective tissue disease, we studied 14 patients, classified according the criteria of Kasukawa et al. The patient records were studied retrospectively and all patients were examined in a 1-day follow-up program. Systemic lupus erythematosus and polymyositis/dermatomyositis-like symptoms disappeared in time, whereas scleroderma-like symptoms (such as in the Raynaud phenomenon) and joint abnormalities persisted. Extensive limitation of joint function was found in four patients. At the time of follow-up, no active renal disease was found. Thrombocytopenia was still present in one of the three patients who had had this feature. All patients had abnormalities of esophageal motility. Long-term corticosteroid treatment was associated with aseptic bone necrosis in three patients and growth retardation in one. We conclude that the Kasukawa criteria are easy to apply to children, and that juvenile-onset mixed connective tissue disease has many similarities to the adult form of the disease.

Objective: To evaluate correlations between changes in anti-U1 RNA antibody levels and disease activity in 9 patients with systemic lupus erythematosus (SLE) overlap syndrome who were prospectively followed up for at least 3 years., Methods: Anti-U1 RNA antibody levels were measured quantitatively, using a nitrocellulose filter binding assay. Disease activity was measured with a validated SLE activity index., Results: All 9 major disease exacerbations were associated with peaks in anti-U1 RNA antibody level., Conclusion: These results seem to indicate that measuring anti-U1 RNA antibody levels can be useful for monitoring disease activity.

In a three year prospective study disease activity variables and levels of antibody against the RNP-peptides 70K and A were measured in 18 patients with mixed connective tissue disease. Antibody measurement entailed use of cloned autoantigens in an enzyme linked immunosorbent assay (ELISA). Fluctuations in antibody levels against 70K and A were most commonly noted in patients who also had changes in disease activity, but these changes in serology and disease activity were synchronous in only a minority of the episodes. Even major disease flares were associated with changes in anti-A levels in only a few, and with changes in anti-70K levels in none of the episodes. The data indicate that measurements of anti-70K and anti-A levels are not useful in monitoring disease activity or response to treatment in mixed connective tissue disease, and suggest that these antibody specificities do not play a direct part in the pathogenesis of disease manifestations.

Several micro-organisms, especially viruses, have been associated with juvenile and adult onset Still's disease. In the present study a search for probable triggering viral infections in five consecutive patients with early, active adult onset Still's disease has been made. In one patient echovirus 7 was identified as a probable triggering agent. Evidence of infection with this virus was acquired by virus cultures and serological tests. In two patients the illness was probably initiated by a rubella reinfection. Both had initially high stable monospecific IgG antibody titres but no IgM antibodies to this virus. In the remaining two cases no particular triggering viral infection could be designated. Evidence of a viral infection was thus found in three of these five patients. Adult onset Still's disease may represent a reaction pattern to certain infections.

A novel frequently occurring autoantibody specificity in serum from connective tissue disease patients is described. The autoantibodies as detected by immunoblotting are directed against a 56,000 Dalton (56K) antigen, that after biochemical fractionation predominantly is found in the cytoplasmic fraction of various cell types and tissues. Attempts to localize the antigen more precisely were unsuccessful primarily because these antibodies do not produce a positive immunofluorescence pattern. The antigen in its native form is not associated with DNA or one of the common cytoplasmic or nuclear RNAs in the cell. Immunoprecipitation studies also showed that the protein is not closely associated with other proteins in a multi-component complex. Anti-56K antibodies are found in about 8% of patients with connective tissue disease, most commonly in patients with Sjögren's syndrome (14%). It is not found in patients with mixed connective tissue disease, polymyositis/dermatomyositis or scleroderma and rarely (less than 1%) in healthy control subjects. The fact that 22% of the anti-56K sera also contain La/SS-B antibodies support the idea that this antibody specificity might be characteristic for a subclass of Sjögren's syndrome patients.

By means of a case-control study we investigated the association between HLA phenotypes and the development of proteinuria after aurothioglucose or D-penicillamine treatment in patients with rheumatoid arthritis (RA). HLA-DR3 was markedly increased in 44 treatment cases compared with 66 RA controls (46 versus 18%, p = 0.002). HLA-DR3 positive patients were at greater risk during treatment with D-penicillamine (RR 10.1, p = 0.001) than gold treated cases (RR 1.7, p = 0.365). The associations between HLA-DR3 and nephrotic syndrome (RR = 6.3, p = 0.004) and early onset proteinuria (RR = 5.4, p less than 0.001) were stronger compared with uncomplicated proteinuria (RR = 3.1, p = 0.017) and late-onset proteinuria (RR = 1.6, p = 0.459), respectively. It appears that genetic factors in RA influence the development, the degree and the time of onset of drug induced proteinuria.

Sera of 34 patients with progressive systemic sclerosis and of 11 patients with polymyositis/dermatomyositis (PM/DM) were analyzed by the immunoblotting technique for the presence of marker antibodies. The presence of anti-centromere, anti-Topoisomerase-I (anti-Topo-I) and anti-Jo-1 antibodies was found to be highly specific for the CREST syndrome, diffuse scleroderma and PM/DM, respectively, but only of limited sensitivity (78, 44 and 45%, respectively). Anti-Topo-I positive diffuse scleroderma patients had a more severe disease (digital pitting scars and renal insufficiency) than anti-Topo-I negative diffuse scleroderma patients. Anti-Jo-1 was associated with interstitial lung disease. Longitudinal studies showed a constant antibody pattern. Our results confirm the clinical usefulness of these marker antibodies.

A human cDNA expression library was screened with anti-ribonucleoprotein (RNP) antibodies from patients with connective tissue diseases. Three cDNA clones were isolated encoding 70 kD, A and B" ribonucleoprotein autoantigens which were expressed as beta-galactosidase fusion proteins. Antigens were purified and used to develop sensitive ELISAs suitable for the routine screening of large series of sera from patients with connective tissue diseases. More than 400 sera were tested both by ELISA and by immunoblotting. The ELISA was found to be at least as sensitive as immunoblotting and very specific. Anti-70 kD antibodies were found in 94% of patients with mixed connective tissue disease (MCTD), in 4% of patients with other connective tissue diseases but not in normal controls. Furthermore, the use of recombinant 70 kD antigen enabled us to discriminate between anti-70 kD antibodies present in anti-Sm and in anti-(U1) RNP sera. Recombinant A antigen contained at least two autoantibody-reactive sites; one unique for the A protein and another cross-reactive with anti-B" antibodies. Antibodies reactive with the unique site were found in 83% of MCTD patients, in 4% of patients with other connective tissue diseases and not in normal controls. Antibodies against the cross-reactive B" epitope present on A and B" recombinant antigens, were found in high titres in a small percentage of patients with systemic lupus erythematosus (SLE, 5%) and rheumatoid arthritis (RA, 2%).

A quantitative immunoblotting assay (QIBA) for the determination of specific antibody titres in human autoimmune sera is described. In this assay, a total HeLa nuclear protein fraction, immobilized on nitrocellulose blot strips, was used as source of antigens and immunoreactive species of autoantibodies were quantitated by an enzyme linked second antibody procedure. Besides being more discriminative, QIBA appeared to be up to 500 times more sensitive than immunodiffusion or immunoelectrophoresis. In this study we used 21 sera from patients with SLE or MCTD for a quantitative analysis of their specific autoantibody content. Within this group, a very diverse spectrum of antibody populations was observed; anti-RNP sera appeared to contain, among others, high tired antibody versus 70K and 31K polypeptides while all (n = 6) anti-Sm sera recognized a 25kD protein doublet. In a follow-up study of two MCTD patients significant flares in specific antibody content could be observed.

Using the immunoblotting technique, sera from 433 patients with rheumatic diseases were screened for the presence of antibodies against several nuclear and cytoplasmic antigens, such as RNP, Sm, Ro(SSA), La(SSB), CR-19 (centromeric antigen), Topo-1 (Scl-70), Jo-1, histone and 56 kD. At the same time clinical data from these patients were collected without prior knowledge of the immunoblotting results. Syndrome-specific autoantibodies were found for mixed connective tissue disease (antibodies against the RNP related 70 kD antigen), for CREST (anti-CR-19 antibodies), for diffuse scleroderma (anti-Topo-1 antibodies) and for polymyositis (anti-Jo-1 antibodies). Almost all specific autoantibodies were present exclusively in patients with a connective tissue disease. Controls were only in a few cases positive for antihistone and anti-56 kD antibodies. Associations of specific autoantibodies with clinical and laboratory features of the patients were mostly as expected. However, some unexpected associations were found, for example polymyositis and calcinosis with anti-Sm antibodies, sicca symptoms with anti-centromere antibodies and leucopenia with Ro(SSA) and La(SSB).

Specific nuclear proteins, separated according to their molecular weight (mol. wt) by polyacrylamide gel electrophoresis (PAGE) and subsequently transferred to nitrocellulose sheets, are able to bind antibodies in sera from patients suffering from different types of connective tissue diseases. Antibodies against a characteristic set of nuclear protein antigens are found in sera from patients with mixed connective tissue disease (MCTD). Screening of 21 MCTD sera revealed a typical immunoblot pattern with major protein antigens of mol. wt 70,000 (20/21) (not identical with the Scl-70 antigen characteristic for scleroderma), mol. wt 31,000 (17/21), two proteins around mol. wt 23,000 (15/21) and two around mol. wt 19,000 (10/21). The 70,000, 23,000 and 19,000 antigens appeared to be rather insoluble nuclear proteins (i.e. components of the nuclear matrix). On behalf of their structural character they were present in nuclei from several types of cells but only in low amounts detectable in salt extracts of thymus acetone powder. The presence of antibodies directed against the mol. wt 70,000 antigen correlated strongly with the diagnosis of MCTD. This 70,000 antigen is not identical with the RNP antigen, a soluble ribonuclease sensitive ribonucleoprotein, since antibodies against nuclear RNP can be separated from anti-nuclear matrix antibodies by affinity chromatography using immobilized thymus salt extract. The distinct character of soluble nuclear RNP and structural nuclear matrix antigens is further supported by the fact that from 14 other anti-RNP sera obtained from patients with systemic lupus erythematosus (SLE), only three contained antibodies against the mol. wt 70,000 protein. Since the immunoblot pattern obtained with MCTD sera mostly was clearly distinguishable from the patterns obtained with sera from patients with related connective tissue diseases our results suggest that the immunoblotting technique might be useful as a diagnostic tool and support the concept of MCTD as a distinct entity.