[Autoantibody diagnostics in idiopathic inflammatory myopathy]

Idiopathic inflammatory myopathy (IIM) is a group of rare and heterogeneous systemic diseases that manifest not only in the muscles but also in the skin, joints, and lungs. Initial symptoms can be isolated and variable and thus the diagnosis poses challenges to various specialist groups. As autoantibodies are sometimes the only specific findings that lead to the diagnosis and appropriate treatment, basic knowledge of them is essential. This article explains the available test systems, names the clinical indications necessary for the initiation of autoantibody diagnostics, provides information on the etymology, antigens, synonyms, and first descriptors, describes indirect immunofluorescence on HEp‑2 cells induced by myositis antibodies, and provides clinical-serological associations. The comparison of the autoantibody findings with the clinical symptoms and laboratory findings enables the identification of false positive or false negative laboratory findings in the sense of a plausibility check.

[Antinuclear antibodies without connective tissue disease : Antibodies against LEDGF/DSF70]

Testing for antinuclear antibodies (ANA) by the indirect immunofluorescence test (IFT) is regarded as a fundamental serological screening method for diagnosing connective tissue diseases (CTD). In the case of a negative result exclusion of certain CTDs is indicated, especially systemic lupus erythematosus, and a positive ANA result is the starting point for further tests aimed at finding disease-specific autoantibodies. The recently discovered antibodies against lens epithelium-derived growth factor (LEDGF/DSF70) deviate from the normal interpretation pattern in ANA diagnostics. These antibodies give rise to a characteristic dense fine speckled (DSF) immunofluorescence pattern in IFT and target the ubiquitously expressed nuclear stress protector protein LEDGFp75. They can be detected, sometimes in high titers, not only in patients with diverse disorders of the skin or eyes and with neoplasms but also in persons with relatively mild or unspecific complaints and even in apparently healthy individuals; however, they are less frequent in CTD. These anti-LEDGF antibodies can be found in all age groups with a tendency to a higher prevalence in younger people and the frequency does not increase in advanced age. The vast majority of anti-LEDGF carriers are female. The CTDs with isolated anti-LEDGF antibodies, i. e. unaccompanied by autoantibodies typical for the respective CTD, are extremely rare. Detection of ANA exclusively with a DSF immunofluorescence pattern and confirmed by a specific anti-LEDGF binding assay, does not therefore indicate the presence of CTD but is indicative of exclusion of systemic lupus erythematosus, systemic sclerosis and an ANA-associated overlap syndrome, similar to a completely negative ANA result.

Frequency of disease-associated and other nuclear autoantibodies in patients of the German Network for Systemic Scleroderma: correlation with characteristic clinical features

Introduction

In the present study, we analysed in detail nuclear autoantibodies and their associations in systemic sclerosis (SSc) patients included in the German Network for Systemic Scleroderma Registry.

Methods

Sera of 863 patients were analysed according to a standardised protocol including immunofluorescence, immunoprecipitation, line immunoassay and immunodiffusion.

Results

Antinuclear antibodies (ANA) were detected in 94.2% of patients. In 81.6%, at least one of the autoantibodies highly associated with SSc or with overlap syndromes with scleroderma features was detected, that is, anti-centromere (35.9%) or anti-topoisomerase I (30.1%), followed in markedly lower frequency by antibodies to PM-Scl (4.9%), U1-ribonucleoprotein (U1-RNP) (4.8%), RNA polymerases (RNAPs) (3.8%), fibrillarin (1.4%), Ku (1.2%), aminoacyl-transfer RNA synthetases (0.5%), To (0.2%) and U11-RNP (0.1%). We found that the simultaneous presence of SSc-associated autoantibodies was rare (1.6%). Furthermore, additional autoantibodies were detected in 55.4% of the patients with SSc, of which anti-Ro/anti-La, anti-mitochondrial and anti-p25/p23 antibodies were most frequent. The coexistence of SSc-associated and other autoantibodies was common (43% of patients). SSc-associated autoantibodies disclosed characteristic associations with clinical features of patients, some of which were previously not acknowledged.

Conclusions

This study shows that five autoantigens (that is, centromere, topoisomerase I, PM-Scl, U1-RNP and RNAP) detected more than 95% of the known SSc-associated antibody responses in ANA-positive SSc patients and characterise around 79% of all SSc patients in a central European cohort. These data confirm and extend previous data underlining the central role of the determination of ANAs in defining the diagnosis, subset allocation and prognosis of SSc patients.

Autoantibody detection using indirect immunofluorescence on HEp-2 cells

The detection of autoantibodies is an important element in the diagnosis and monitoring of disease progression in patients with autoimmune diseases. In laboratory diagnostic tests for connective tissue and autoimmune liver diseases, indirect immunofluorescence on HEp-2 cells plays a central role in a multistage diagnostic process. Despite the high quality of diagnostics, findings at different laboratories can differ considerably due to a lack of standardization, as well as subjective factors. The present paper formulates recommendations for the standardized processing and interpretation of the HEp-2 cell test for the detection of non-organ-specific (especially antinuclear) antibodies. It provides requirements regarding the diagnostic tests used, instructions for laboratory procedure and evaluation, and recommendations for interpretation. For an optimal laboratory diagnostic process, it is useful to have an informative, tentative clinical diagnosis and an experienced laboratory diagnostician. In addition, the following key elements are recommended: initial screening using indirect immunofluorescence on carefully chosen HEp-2 cells beginning with a serum dilution of 1:80 and evaluation under a microscope with powerful illumination; results from a titer of 1:160 upwards being considered positive; internal laboratory quality control; and standardized interpretation. The aim is to improve diagnostic tests and care of patients with autoimmune diseases as a central concern of the European Autoimmunity Standardization Initiative (EASI).

No association between systemic sclerosis and C77G polymorphism in the human PTPRC (CD45) gene

OBJECTIVE

The functional variant C77G (rs17612648) of PTPRC (CD45) was described to confer risk for systemic sclerosis (SSc) in German Caucasians. We analyzed this association in an independent, larger German cohort.

METHODS

We genotyped 171 cases and 179 controls. Cases were subgrouped according to sex, autoantibody profiles, or clinical subsets.

RESULTS

No association of SSc with C77G was detected in the whole dataset, in subgroups, or in combined analyses with a previous study.

CONCLUSION

The results do not confirm PTPRC C77G as a general and independent risk factor for development of SSc.

Clinical diagnosis compared to classification criteria in in a cohort of 54 patients with systemic sclerosis and associated disorders

OBJECTIVE

To compare clinical diagnosis with two validated classification criteria for systemic sclerosis (SSc) in a cohort of Swiss patients with SSc and associated disorders.

METHODS

Charts of 54 patients with SSc and associated disorders were reviewed and compared with data obtained at a thorough clinical examination using a standardised protocol (Raynaud's phenomen [RP], skin involvement, nailfold capillary microscopy and determination of autoantibody pattern).

RESULTS

According to patient records 6 patients had diffuse cutaneous SSc (dcSSc), 23 limited cutaneous SSc (lcSSc) and 20 were not classified. Two patients had mixed connective tissue disease (MCTD) and 3 overlap syndromes. At the time of clinical examination, 7 patients showed dcSSc (6 plus 1 patient originally classified as lcSSc), 26 lcSSc (20 plus 6 originally not classified) and 16 patients had severe RP which was arbitrarily classified as Raynaud's syndrome (RS). 15 of the latter 16 were antinuclear antibody positive and 7 exhibited pathological nailfold capillaries. On the basis of LeRoy and Medsger's criteria, 6 of these patients could be further classified as limited SSc (lSSc). Of 49 sera tested, 14 contained centromere antibodies at clinical examination, 16 Scl-70, 5 RNA-pol, 1 Ku, 12 antibodies with unknown specificity, and one serum was autoantibody negative.

CONCLUSIONS

A substantial number of patients with minor cutaneous manifestations do not fulfil ACR classification criteria, though they have typical clinical signs of SSc. Characteristic features in these patients are presence of Raynaud's phenomenon, antinuclear antibodies and pathological changes in nailfold capillary microscopy. Application of the diagnostic criteria recently proposed by LeRoy and Medsger makes it possible to name many of these patients. The use of these criteria is recommended for clinical management.

Clinical diagnosis compared to classification criteria in in a cohort of 54 patients with systemic sclerosis and associated disorders

OBJECTIVE

To compare clinical diagnosis with two validated classification criteria for systemic sclerosis (SSc) in a cohort of Swiss patients with SSc and associated disorders.

METHODS

Charts of 54 patients with SSc and associated disorders were reviewed and compared with data obtained at a thorough clinical examination using a standardised protocol (Raynaud's phenomen [RP], skin involvement, nailfold capillary microscopy and determination of autoantibody pattern).

RESULTS

According to patient records 6 patients had diffuse cutaneous SSc (dcSSc), 23 limited cutaneous SSc (lcSSc) and 20 were not classified. Two patients had mixed connective tissue disease (MCTD) and 3 overlap syndromes. At the time of clinical examination, 7 patients showed dcSSc (6 plus 1 patient originally classified as lcSSc), 26 lcSSc (20 plus 6 originally not classified) and 16 patients had severe RP which was arbitrarily classified as Raynaud's syndrome (RS). 15 of the latter 16 were antinuclear antibody positive and 7 exhibited pathological nailfold capillaries. On the basis of LeRoy and Medsger's criteria, 6 of these patients could be further classified as limited SSc (lSSc). Of 49 sera tested, 14 contained centromere antibodies at clinical examination, 16 Scl-70, 5 RNA-pol, 1 Ku, 12 antibodies with unknown specificity, and one serum was autoantibody negative.

CONCLUSIONS

A substantial number of patients with minor cutaneous manifestations do not fulfil ACR classification criteria, though they have typical clinical signs of SSc. Characteristic features in these patients are presence of Raynaud's phenomenon, antinuclear antibodies and pathological changes in nailfold capillary microscopy. Application of the diagnostic criteria recently proposed by LeRoy and Medsger makes it possible to name many of these patients. The use of these criteria is recommended for clinical management.

Labordiagnostik bei systemischer Sklerose

For systemic sclerosis, laboratory tests can play a supplementary role to clinical investigations, imaging techniques and functional tests. Typical autoantibodies support early diagnosis and help in assigning patients to subgroups of the disease; negative results for antinuclear antibodies suggest exclusion of the diagnosis. To detect organ involvement and comorbidity, the laboratory contributes by clinical chemistry, in certain cases by histopathological findings and by the cytological assessment of broncho-alveolar lavage fluid. Inflammatory parameters are of minor importance. Multiple autoantibody determinations in the course of the disease are not yet helpful. Numerous additional laboratory parameters are of value for investigating pathogenesis, but have not yet been generally introduced into the routine diagnostics of systemic sclerosis.

Sklerodermie-assoziierte Autoantikörper – klinische und diagnostische Relevanz

In systemic sclerosis (SSc) and its variants, autoantibodies are the best known immunological aberration. In more than 95% of the patients, antinuclear antibodies or other autoantibodies can be detected. In about 90% of SSc patients with antinuclear antibodies, scleroderma associated autoantibodies highly specific for systemic sclerosis are found. These autoantibodies usually exclude each other in individual patients, and they are detectable early, persisting during the course of the disease. SSc patients characterized by scleroderma associated autoantibodies belong to disease subsets which are relatively homogeneous in clinical, genetic and prognostic terms. Besides these diagnostically relevant autoantibodies, numerous additional ones have also been described. These are neither SSc specific nor mutually exclusive, and their antigens have only been partially characterized. Some, however, are thought to be relevant to the as yet unanswered question of whether autoantibodies are directly involved in SSc pathogenesis.

Diagnosis and prognosis of early rheumatoid arthritis, with special emphasis on laboratory analysis

Diagnosis of rheumatoid arthritis (RA) is mainly based on clinical criteria of symmetric polyarthritis of the hands and feet, with morning stiffness lasting usually more than 1 h. Autoantibodies typical for RA, i.e., rheumatoid factors and anti-cyclic citrullinated peptide, and measurements of inflammation add more specific information, especially for early diagnosis, where clinical presentation may be oligosymptomatic involving only a few joints. These laboratory parameters are also relevant for prognosis of disease persistence, functional impairment and radiological progression.

[New aspects in autoantibody diagnosis in collagen diseases]

Distinct, especially non-organ specific autoantibodies are closely associated with connective tissue diseases and in many cases are vital elements of the laboratory diagnostics of these disorders. Their inclusion into the common classification criteria is quite heterogeneous. None of the autoantibodies is 100% specific for a certain disease, and diagnostic specificity is usually reduced when application of the test is broadened and when more sensitive methods are used. In individual patients with scleroderma and/or myositis related diseases, typical autoantibodies usually exclude each other; however, there are characteristical exceptions from that rule. Evidence is accumulating that autoantibodies are detectable early during disease course and often even in preclinical stages. Variations of antibody levels during disease course are different in different systems and in some cases have been shown to correlate with disease activity. Negative results in sensitive screening assays are often essential to exclude a connective tissue disease. Although it has certain drawbacks and is being disputed, the indirect immunofluorescence assay with HEp-2 cells still serves as a standard first step in connective tissue disease-related antibody detection. In case of positive results in this assay, further steps should be performed carefully, considering the signs and symptoms of the suspected disease as well as the immunofluorescence pattern, and being aware of the peculiarities and limitations of the assay methods used.

Development of a CENP-A/CENP-B-specific immune response in a patient with systemic sclerosis

Antibodies directed against an epitope motif on CENP-A have been shown to cross-react with mimotopes on other autoantigens and on Epstein-Barr nuclear antigen 1 (EBNA-1), suggesting a molecular mimicry. We describe here the gradual development of an anticentromere immune response in a patient with systemic sclerosis, which started from an antihistone response and was not mediated by molecular mimicry. Via an epitope on histone H3, the antibody response spread to a homologous epitope in the H3 homology domain of CENP-A. This was followed by an intramolecular epitope spreading to N-terminal peptides of CENP-A containing the known epitope motif G-P-X(1)-R-X(2). From there it spread to corresponding epitopes on CENP-B and to mimotopes of the major CENP-A epitope motif on other autoantigens including EBNA-1. Whether the D-penicillamine treatment received by this patient was involved in the triggering of this cascade remains a matter of speculation.

Coexistence of antitopoisomerase I and anticentromere antibodies in patients with systemic sclerosis

BACKGROUND

Antibodies targeting DNA topoisomerase I (ATA) or centromere proteins (ACA) are associated with clinical subsets of patients with systemic sclerosis (SSc). The occurrence of those autoantibodies is considered to be mutually exclusive.

OBJECTIVE

To describe the clinical and immunogenetic data of three patients who are co-expressing both antibodies, and then review previous publications.

METHODS

Both antibodies were detected by different methods, including indirect immunofluorescence technique, enzyme linked immunosorbent assay, immunodiffusion, and immunoblot. Patients were HLA typed by serological and molecular genetic methods. Data were extracted from published reports for comparison. The search for published studies was through Medline and other database research programmes.

RESULTS

During routine laboratory diagnostics over several years three patients with scleroderma and coincidence of ATA and ACA were identified: patient 1 with diffuse SSc, Raynaud's phenomenon, puffy fingers and fingertip necrosis, contractures, and calcinosis; patient 2 with diffuse SSc, Raynaud's phenomenon, oedema of the hands, and interstitial calcinosis of hands, knees, and shoulders, and pulmonary fibrosis; patient 3 with scleroderma of hands, forearms, and face, Raynaud's phenomenon, puffy fingers, finger contractures, fingertip necrosis, and calcinosis. All three patients studied were carriers of HLA alleles known to be associated with these autoantibodies. In serial measurements the concentrations of the two antibodies showed independent or even reverse fluctuations. Screening of 100 patients with ACA for ATA and vice versa disclosed no further patients with coincidence of these antibodies. Twenty eight cases of ACA/ATA coexistence in 5423 patients (0.52%) with SSc or SSc associated symptoms were found in an analysis of published studies.

CONCLUSION

The expression of ATA and ACA is not totally mutually exclusive, but coincidence is rare (<1% of patients with SSc). Patients with both autoantibodies often have diffuse scleroderma and show immunogenetic features of both antibody defined subsets of SSc.

Autoantibodies directed to novel components of the PM/Scl complex, the human exosome

The autoantigenic polymyositis/scleroderma (PM/Scl) complex was recently shown to be the human homologue of the yeast exosome, which is an RNA-processing complex. Our aim was to assess whether, in addition to targeting the known autoantigens PM/Scl-100 and PM/Scl-75, autoantibodies also target recently identified components of the PM/Scl complex. The prevalence of autoantibodies directed to six novel human exosome components (hRrp4p, hRrp40p, hRrp41p, hRrp42p, hRrp46p, hCsl4p) was determined in sera from patients with idiopathic inflammatory myopathy (n = 48), scleroderma (n = 11), or the PM/Scl overlap syndrome (n = 10). The sera were analyzed by enzyme-linked immunosorbent assays and western blotting using the affinity-purified recombinant proteins. Our results show that each human exosome component is recognized by autoantibodies. The hRrp4p and hRrp42p components were most frequently targeted. The presence of autoantibodies directed to the novel components of the human exosome was correlated with the presence of the anti-PM/Scl-100 autoantibody in the sera of patients with idiopathic inflammatory myopathy (IIM), as was previously found for the anti-PM/Scl-75 autoantibody. Other clear associations between autoantibody activities were not found. These results further support the conception that the autoimmune response may initially be directed to PM/Scl-100, whereas intermolecular epitope spreading may have caused the autoantibody response directed to the associated components.

A population of autoantibodies against a centromere-associated protein A major epitope motif cross-reacts with related cryptic epitopes on other nuclear autoantigens and on the Epstein-Barr nuclear antigen 1

Autoimmune diseases arise from a host's immune response against self-antigens. The triggering events ultimately resulting in such a break of tolerance are largely unknown. It is also not known why certain molecular structures become autoantigenic. The hypothesis has long been proposed that autoimmune diseases arise from molecular mimicry followed by an epitope spreading mechanism. Recently we have shown that the anti-centromere-associated protein A (CENP-A) immune response is directed against an autoantigenic motif, G/A-P-R/S-R-R, that occurs three times in the N-terminal amino acids of CENP-A. In the present study we used mutational analyses with immobilized oligopeptide arrays to identify the amino acids in this motif that are responsible for antibody binding. In particular, we found that surprisingly mimotopes of this motif are present in a vast number of autoantigens and in the Epstein-Barr nuclear antigen 1. With affinity-purified antibodies we show that the antibodies against this motif are polyclonal and cross-react with several autoantigens. However, in these autoantigens this motif often represents a cryptic epitope explaining the obvious conflict between our results and the known high specificity of autoantibodies. The presence of such an ubiquitous structure on autoantigens suggests a novel peptide-driven mechanism for the evolution of autoantibodies.

Fine-specificity of the anti-CENP-A B-cell autoimmune response

The major targets recognized by anti-centromere autoantibodies are the three centromere-associated proteins (CENPs) A, B, and C, with apparent molecular masses of 19, 80, and 140 kDa, respectively. Previously a major epitope region on the 19-kDa CENP-A antigen was identified by synthesis of a soluble synthetic 15-mer peptide (amino acids 3-17) to be used in enzyme-linked immunosorbent assay and western blot competition assays. However, no systematic experimental scanning for epitope regions on the CENP-A autoantigen has yet been performed. In this study we scanned the complete CENP-A amino acid sequence for epitopes using 19 previously characterized autoimmune-sera. Overlapping peptides 15 amino acids in length and offset by three amino acids were synthesized on activated membranes, covering the whole CENP-A autoantigen. Probing of the membranes with various anti-centromere sera showed that all epitopes are clustered in the N-terminal 45 amino acids. For fine-mapping of this autoreactive region the N-terminus of CENP-A (amino acids 1-45) was scanned again by probing overlapping 15-mer, 12-mer, 10-mer, 8-mer, 7-mer, 6-mer, and 5-mer peptides, all offset by one amino acid, with anti-centromere sera. In this way we localized two epitope core regions within the N-terminal 45 amino acids, one covering amino acids 2-17, recognized by 17 sera, and the other covering amino acids 22-38, recognized by 18 sera. One serum did not react with CENP-A at all. Several sera seem to recognize overlapping individual epitopes within these two epitope core regions. All sera, however, recognize a sequence motif G/A-P-R/S-R-R.

Clinical and serological aspects of patients with anti-Jo-1 antibodies--an evolving spectrum of disease manifestations

The aim of this study was to compare ELISA, immunodiffusion and immunoblot for the detection of anti-Jo-1 antibodies, and to investigate the association of the results with clinical manifestations. In two medical centres for rheumatology and one for pulmonology, all patients with suspected connective tissue disease were screened over a 5-year period for anti-Jo-1 antibodies by ELISA. Positive sera were controlled in another laboratory by immunodiffusion. If immunodiffusion was negative, sera were controlled again by ELISA. ELISA-positive immunodiffusion-negative sera were tested by immunoblotting. The patients were characterised clinically, and their clinical signs and symptoms were compared with those of 257 patients with anti-Jo-1 antibodies published in 15 case series and 30 case reports. Twenty-five patients had a positive ELISA test. Fifteen sera were positive by ELISA and immunodiffusion (group 1). Three sera showed high titres in both ELISA tests with negative immunodiffusion and immunoblot (group 2). Seven sera showed low titres in both ELISA tests. The results were negative in the other tests (group 3). Patients in groups 1 and 2 could be classified as Jo-1 syndrome patients. Of these 18 patients, 15 had arthritis, 14 had myositis and 14 had interstitial lung disease. Only four patients had myositis at disease onset. We describe four unusual patients with Jo-1 syndrome in detail: 1. Long history of seronegative rheumatoid arthritis; 2. Sjögren's syndrome with Ro- and La-antibodies; 3. Scleroderma and bronchial carcinoma with centromere antibodies; 4. Corticoid-sensitive psychosis. Patients with suspected connective tissue disease may be screened for anti-Jo-1 antibodies by ELISA. It detects some patients that are missed by immunodiffusion. Especially lower ELISA titres should be controlled by another method because of the low specificity of the test. The clinical picture is variable. Most patients have features other than myositis at disease onset.

Strong association of dermatomyositis-specific Mi-2 autoantibodies with a tryptophan at position 9 of the HLA-DR beta chain

OBJECTIVE

To characterize the clinical and immunogenetic features of patients with Mi-2 autoantibodies.

METHODS

Eighteen adult white patients with Mi-2 antibodies were clinically characterized and compared with 41 Mi-2-negative dermatomyositis (DM) patients. HLA class I and class II typing for DRB alleles was done by microcytotoxicity assay and for DQA and DQB alleles by polymerase chain reaction-based oligotyping.

RESULTS

Seventeen of the 18 Mi-2-positive patients had DM. Symptoms of scleroderma, lung involvement, and arthritis were less common in this group than in the Mi-2-negative DM patients; the V-sign rash and nailfold involvement were found more frequently. Mi-2 antibodies were strongly associated with HLA-DR7 (88% versus 24% in healthy controls), HLA-DQA1*0201 (86% versus 23%), and DR7 "homozygosity" (31% versus 0%). A tryptophan residue at position 9 of the HLA-DR beta chain was present in all Mi-2-positive patients (100% versus 62%; homozygous in 81% versus 15%).

CONCLUSION

Our results reemphasize the specificity of Mi-2 antibodies for DM, and extend previous reports that Mi-2 antibody production is associated with certain HLA class II antigens. We propose beta 9-Trp as a candidate epitope on the HLA-DR beta chain as a prerequisite for this type of autoimmune response.

[Diagnostic significance of scleroderma and myositis-associated autoantibodies]

In more than 95% of patients with systemic sclerosis and in about 60% of patients suffering from idiopathic inflammatory myopathies autoantibodies directed at different nuclear or cytoplasmic antigens can be detected with different methods. Scleroderma-associated autoantibodies can be visualized as antinuclear antibodies (ANA) by immunofluorescence assays using cultured monolayer cells. In case of a negative ANA result the diagnosis of systemic sclerosis is unlikely. In individual patients the different autoantibodies (against DNA topoisomerase I (Scl-70), centromeric antigens, fibrillarin, To (Th), RNA polymerases, NOR-90, U1-nRNP, PM-Scl, Ku) are mutually exclusive. They can be detected early in the course of diseases, most often are persistent, and are closely associated with immunogenetic markers. They are characteristic for distinct subsets of patients homogeneous in clinical manifestations as well as in disease outcome. Myositis-associated autoantibodies are directed to nuclear (about 60% of myositis patients; PM-Scl, Mi-2) or cytoplasmic antigens (about 35-40%; Jo-1 and other aminoacyl-tRNA-synthetases, signal recognition particle (SRP), KJ and others) and likewise are related to distinct clinical, prognostic, and immunogenetic traits leading to the description of characteristic antibody-based syndromes. Based on published results and on our own investigations, the diagnostic potential of scleroderma- and myositis-associated antibodies is evaluated and a new classification of systematic myositic and sclerodermatous disease is proposed.

Clinical relevance and HLA association of autoantibodies against the nucleolus organizer region (NOR-90)

OBJECTIVE

NOR-90 autoantibodies directed against the nucleolus organizer region (NOR) have been described as rare scleroderma associated antibodies. We studied the clinical features of patients with NOR-90 antibodies as well as their HLA phenotype.

METHODS

NOR-90 antibodies were detected by indirect immunofluorescence assay using HEp-2 cells, by chromosome spreads as a substrate and in addition by Western blot analysis with HeLa-S3 nucleolar extract. HLA antigens of the NOR-90 antibody positive patients were typed with the standard NIH complement dependent microcytotoxicity test.

RESULTS

Nine sera selected by means of the indirect immunofluorescence revealed a typical double band pattern of about 90 kDa identical with the pattern of 2 NOR-90 reference sera by Western blot analysis. Only one patient positive for NOR-90 antibodies suffered from systemic sclerosis (limited cutaneous scleroderma). The other patients with NOR-90 antibodies showed no signs of systemic sclerosis. All patients with NOR-90 antibodies were women and 8 of 9 patients (89 versus 13% of healthy controls, Pcorr < 0.001) were positive for the HLA-DR1 allele.

CONCLUSION

In contrast to the first report on NOR-90 antibodies we demonstrated no association of these antibodies with systemic sclerosis; however, we found strong evidence for an immunogenetic background of NOR-90 antibody formation.

Persistence of a rheumatoid factor (RF)-producing B cell clone with a somatically mutated Ig kappa chain in a patient with rheumatoid arthritis

The V kappa IV gene encoding the light chain of an IgA has been shown to have undergone 31 somatic mutations compared with the single existing V kappa IV germ-line gene. We now show the persistence of the rearranged and mutated DNA coding for this RF over a period of 5 years in the peripheral blood lymphocytes (PBL) of the patient with rheumatoid arthritis (RA). The sequence of the RF has been conserved to identity over this period. These results raise the possibility that the particular antigenic stimulus leading to RF production in this RA patient is active over a long period of time.

A somatically mutated V kappa IV gene encoding a human rheumatoid factor light chain

The light chain of an IgA kappa rheumatoid factor (RF) produced by a hybridoma derived from a patient with rheumatoid arthritis (RA) has been shown to belong to the V kappa IV family. This RF light chain has 31 nucleotide differences compared with the single V kappa IV germline gene reported for the human genome. The patient's V kappa IV germline gene was sequenced, using the polymerase chain reaction (PCR), and shown to be identical to that previously reported. This demonstrates that the RF light chain is the product of a somatically mutated gene. A comparison with other known V kappa IV sequences shows that the RF light chain has more replacement mutations than most of the known V kappa IV light chains.

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

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

Immunogenetic associations of scleroderma-related antinuclear antibodies

Patients selected for the presence of scleroderma-related antibodies (anti-DNA-topoisomerase I [anti-topo I; n = 43], anticentromere antibody [ACA; n = 63], or anti-Pm-Scl [n = 12]) were studied for class I and class II major histocompatibility complex antigens, as well as for Gm and Km allotypes. Anti-topo I was associated with HLA-DR5 (70% of patients versus 30.6% of controls; Pcorr = 0.0018, relative risk [RR] = 5.3). All patients with anti-Pm-Scl were positive for HLA-DR3 (versus 23.5% of controls; Pcorr less than 0.001); 6 of these patients were DR3/4 heterozygous (50% versus 3.5% of controls; Pcorr less than 0.001, RR = 27.3). Patients with ACA were frequently positive for HLA-DR1, DR4, or DRw8, with 73.7% demonstrating at least 1 of these alleles (versus 41.2% of controls; Pcorr = 0.0152, RR = 4.0). This group of ACA-positive patients who had DR1, DR4, and/or DRw8 consisted mainly of a subgroup of patients with rheumatoid arthritis. We conclude that different class II major histocompatibility complex antigens influence the formation of anti-topo I and anti-Pm-Scl. Important clinical differences between these patient groups and the immunogenetic heterogeneity support the notion of different antibody-defined scleroderma subsets.

Immunoglobulin allotype Gm(1,2;21) in ankylosing spondylitis with peripheral arthritis

Frequencies of immunoglobulin G (Gm) allotypes were determined in 240 patients with ankylosing spondylitis (AS). The uncommon phenotype Gm(1,2;21) was increased in frequency in 55 patients with AS and peripheral arthritis (14.5% v 3.5% of healthy blood donors; p less than 0.05). In 16 patients with arthritis only of wrist/hand or ankle/forefoot, or both, the Gm(1,2;21) frequency was even higher (31.3%; p less than 0.0005). Patients with AS negative for the HLA antigen B27 (n = 28) differed from the B27 positive patients (n = 205) with regard to the frequency of the Gm(1,2,3;5,21) phenotype (39.3% v 9.3%; p less than 0.0005). These findings support the notion of genetic heterogeneity among patients with AS.

Antigenic determinants shared between HLA-A, -B, -C antigens and H-2 class I molecules modified by bovine beta-2 microglobulin

The specificity of the mouse class I-specific antibody COB6-3 was examined in detail. It was found to react with the mouse class I molecules H-2Db, Kd, and Qa-2, and with human HLA-A, -B, -C antigens. The specificity pattern of COB6-3, despite its different origin, was similar to that of the monomorphic HLA class I-specific antibody W6/32. Cross-inhibition studies show that on human cells the antigenic determinants recognized by the two antibodies are situated close together and may be identical. On mouse cells, reactivity of both antibodies was generated upon replacement of mouse beta-2 microglobulin (B2m) with its bovine counterpart, but differences in specificity were observed using human B2m.

HLA-DR4 and Gm 1;21 haplotypes are associated with pseudolupus induced by venopyronum dragées

The phenotypic frequencies of human major histocompatibility complex class I, II, and III antigens and immunoglobulin allotypes (Gm factors) were determined in 56 patients (55 women, 1 man) who had lupus-like disease induced by venopyronum dragées. The findings in these patients were compared with those of a control group. We found a significant increase of HLA-DR4 (57.1% versus 26.5%, relative risk [RR] 3.7) and a decrease of HLA-DR3 (3.6% versus 19.1%, RR 0.16) in the patient group. In addition, the haplotype Gm 1;21 (60.7% versus 32.9%, RR 3.2), and the phenotype Gm 1,3;5,21 (46.4% versus 25.8%, RR 2.5) were significantly increased. Both the haplotype Gm 1;21 and the phenotype Gm 1,3;5,21 are associated with HLA-DR4 in pseudolupus patients but not in controls. The coincidence of HLA-DR4 and Gm 1;21 markedly increases the risk of acquiring pseudolupus (RR 6.9). We conclude that the pathogenesis of pseudolupus is influenced by at least 2 independent genetic factors. A similar HLA association has been described in hydralazine-induced lupus, and this suggests a common pathogenic mechanism.

HLA-DR4 and Gm(1,3;5,21) are associated with U1-nRNP antibody positive connective tissue disease

Patients with U1-nRNP antibodies (n = 35, 31 female, four male) were typed for HLA-A, -B, -C, and -DR antigens and IgG heavy chain allotypes G1m(1), -(2), -(3), G3m(5), and -(21). The patient group was clinically heterogeneous. Four met the American Rheumatism Association criteria for systemic lupus erythematosus, six for progressive scleroderma, and 14 for rheumatoid arthritis. Sicca syndrome was present in seven cases. Twenty three had overlapping features compatible with mixed connective tissue disease (MCTD). Healthy blood donors served as controls for HLA typing (n = 64), Gm typing (n = 228), or both (n = 56). Sixty six per cent of the patients with U1-nRNP antibodies were DR4 positive compared with 28% of the controls (relative risk = 4.9, p = 0.00053). The Gm(1,3;5,21) phenotype was found in 46% of the patients and 25% of the controls (relative risk = 2.47, p = 0.0247). Within the patient group Gm(1,3;5,21) was found only in DR4 positive individuals. The coincidence of HLA-DR4 and Gm(1,3;5,21) increases the relative risk values to 8.0 (compared with the group with neither risk factor). DR4 and Gm(1,3;5,21) primarily seem to be related to U1-nRNP antibody formation and not to disease expression. Patients with or without MCTD did not differ with respect to DR4 or Gm(1,3;5,21) frequency. Disease onset was earlier in patients with HLA-DR4/Gm(1,3;5,21) than in patients without both markers (mean 27.9 v 40.1 years; p less than 0.05).

Increased frequency of Gm(1,2;21) phenotype in HLA-DR4 positive seropositive rheumatoid arthritis

Ninety-four patients with seropositive rheumatoid arthritis (RA) were typed for HLA-A, B, C and DR antigens and for immunoglobulin G (Gm) allotypes. Isolated IgG from patient serum was used to avoid interference of IgM rheumatoid factor (RF) with Gm typing in sera with high IgM-RF titer. Besides the association of seropositive RA with the antigen DR4 and an earlier disease onset in DR3/DR4 heterozygotes, we found the uncommon Gm phenotype Gm(1,2;21) significantly more often in our patient group than in healthy controls. Combination of HLA-DR and Gm data shows that individuals with both DR4 and Gm(1,2;21) are at a particularly high disease risk.

Interference of IgM rheumatoid factor with nephelometric C-reactive protein determinations

Different nephelometric assay systems for quantitation of C-reactive protein (CRP) were compared with radial immunodiffusion (RID) and tested for their susceptibility to interference by serum IgM rheumatoid factor (RF). In 3 nephelometric assays, RF was found to elevate CRP values. Sera with high RF content from patients with rheumatoid arthritis gave significantly higher CRP values by nephelometric assay than by RID; the addition of purified RF to RF-negative sera increased CRP values markedly; and removal of RF from sera corrected falsely elevated CRP values. This interference by RF is explained by the action of human RF as a (secondary) antibody reacting with complexed mammalian IgG anti-human CRP in the assay. In this way the nephelometric signal is enhanced to give falsely elevated CRP values. In contrast, the gel diffusion RID method does not suffer from this non-specific interference.