Human autoantibodies against the 70-kd polypeptide of U1 small nuclear RNP are associated with HLA-DR4 among connective tissue disease patients

Towards Early Diagnosis of Mixed Connective Tissue Disease: Updated Perspectives

Mixed Connective Tissue Disease (MCTD) is an autoimmune disease first described by Sharp et al in 1972, characterized by the presence of anti-Ribonucleoprotein antibodies directed against the U1 complex (anti-U1RNP). The condition shares clinical characteristics with Systemic Lupus Erythematosus, Rheumatoid Arthritis, and Systemic Sclerosis. Diagnosis is quite difficult due to its rarity, the lack of validated classification criteria, and its heterogeneous clinical presentation. While in the early stages its nuanced clinical features might lead to it being incorrectly classified as other Connective Tissue Diseases (CTDs) or even not recognized, in cases of longstanding disease its classification as a CTD is clear but challenging to discriminate from overlap syndromes. MCTD should be considered a distinct entity due to the presence of a specific genetic substrate and the presence of the high titer of a specific autoantibody, anti-U1RNP, present in all the commercial kits for Extractable Nuclear Antigens, and almost always associated with Antinuclear Antibody positivity with a coarse speckled pattern. Except for anti-U1RNP, no specific biomarkers are available to guide clinicians to a correct classification of MCTD, which is arrived at by the association of clinical, serological and instrumental evaluation. In the first stages, the disease is mainly characterized by Raynaud's phenomenon, inflammatory arthritis, puffy fingers, myalgia and/or myositis, and rarely, trigeminal neuropathy. Longstanding disease is generally associated with the development of Pulmonary Hypertension and Interstitial Lung Disease, which are the two main causes of mortality in MCTD. The aim of this review is to summarize current knowledge on the early recognition of MCTD.

Capillaroscopy as a diagnostic tool in the diagnosis of mixed connective tissue disease (MCTD): a case report

BACKGROUND

The concept of mixed connective tissue disease (MCTD) as a unique connective tissue disease has endured for half a century. Disease onset can be in adulthood (MCTD) or of juvenile onset (jMCTD) and is characterized by overlapping features of systemic lupus erythematosus (SLE), polymyositis or dermatomyositis (PM/DM) and systemic sclerosis (SSc). No universally accepted classification criteria for MCTD exists, however agreed upon overlapping disease features include the presence of high titers of U1 small nuclear ribonucleoprotein particle antibodies (U1snRNP) in the peripheral blood, Raynaud's phenomenon, synovitis, myositis and swollen hands or fingers. Characteristic capillaroscopy findings are commonly seen in MCTD and jMCTD, which may represent a crucial and key clue for classification as well as prognosis in these patients.

CASE PRESENTATION

We present a young male patient, with symptom onset as early as age 13, who was diagnosed with MCTD at age 16 and found to have high titers of anti-U1snRNP antibodies, Raynaud's phenomenon, synovitis, and swollen hands and fingers. Most interestingly, his video capillaroscopy at diagnosis was abnormal and revealed an active SSc-like pattern. His presentation and course are described.

CONCLUSIONS

We conclude that based on existing data, and as highlighted by this case presentation, nailfold video capillaroscopy should be included as an early screening tool for the detection of microangiopathy in patients with the diagnosis MCTD and jMCTD. Additionally, given its prevalence in this population at disease diagnosis, we recommend consideration be given to nailfold video capillaroscopy as a potentially important classification criteria and prognostic tool for jMCTD and MCTD.

"Mixed connective tissue disease": a condition in search of an identity

Mixed connective tissue disease was first described as a new autoimmune rheumatic disease in 1972 based on the claim of a distinct clinical picture associated with anti-RNP antibody positivity. Subsequently, this new entity has divided opinions in the rheumatology community. We have reviewed recent cohort studies with more than 100 patients, comparing the clinical and immunological features, treatment, prognosis and evolution to well-defined autoimmune rheumatic diseases. We also reviewed clinical features of undifferentiated autoimmune rheumatic diseases based on the most recent studies. After gathering and reviewing these data, we discuss whether the designation “mixed connective tissue disease” should be maintained.

Facts and controversies in mixed connective tissue disease

Mixed connective tissue disease (MCTD) is a systemic autoimmune rheumatic disease (SARD) characterised by the combination of clinical manifestations of systemic lupus erythematosus (SLE), cutaneous systemic sclerosis (SSc) and polymyositis-dermatomyositis, in the presence of elevated titers of anti-U1-RNP antibodies. Main symptoms of the disease are polyarthritis, hand oedema, Raynaud's phenomenon, sclerodactyly, myositis and oesophageal hypomobility. Although widely discussed, most authors today accept MCTD as an independent entity. Others, however, suggest that these patients may belong to subgroups or early stages of certain definite connective diseases, such as SLE or SSc, or are, in fact, SARD overlap syndromes.

Conservation of pathogenic TCR homology across class II restrictions in anti-ribonucleoprotein autoimmunity: extended efficacy of T cell vaccine therapy

T cells have been shown to mediate aspects of anti-ribonucleoprotein (RNP) autoimmunity, and are a potential target of therapy in lupus and related diseases. In this study, we assessed the relevance of a conserved class of anti-RNP T cells to autoimmune disease expression and therapy. Our data show that anti-RNP T cell selection induced a limited set of homologous CDR3 motifs at high frequency. Homologous CDR3 motifs have been reported in other autoimmune diseases. Vaccination with irradiated anti-RNP (but not anti-tetanus toxoid) CD4(+) cells induced remission of anti-RNP-associated nephritis in ≥ 80% of treated mice, even with donor/recipient MHC class II mismatch, and in both induced and spontaneous autoimmunity. Vaccine responder sera inhibited anti-70k T cell proliferation and bound hybridomas expressing the conserved CDR3 motifs. Our data indicate that a limited set of TCR CDR3 motifs may be important for the pathogenesis of anti-RNP lupus and other autoimmune diseases. The ability to target a consistent set of pathogenic T cells between individuals and across class II restrictions may allow for the more practical development of a standardized anti-RNP T cell vaccine preparation useful for multiple patients.

The molecular basis for the presence of two autoimmune diseases occurring simultaneously--preliminary observations based on computer analysis

Specific Human Leukocyte Antigen Class II (HLA II) molecules associated with pemphigus vulgaris (PV), mucous membraine pemphigoid (MMP), and mixed connective tissue disease (MCTD) may react with multiple T cell epitopes within desmoglein 3 (Dsg 3), bullous pemphigoid antigen 2 (BPAG 2), and 70 kDa polypeptide small nuclear ribonucleoproteins (snRNP70) in autoantibody production. We report a group of patients with simultaneous occurrences of PV with MCTD, and MMP with MCTD. In one patient group, we performed serological studies to show presence of antibodies to Dsg 3, Dsg 1, and snRNP70 simultaneously. In the second group, we performed serological studies to show presence of antibodies to BPAG 1, BPAG 2, β4 integrin, and snRNP70 simultaneously. In both groups, HLA II genes were analyzed and the observations were consistent with previously described associations with PV, MMP, and MCTD. It is possible that HLA-DQβ1*0301 allele, present in 10 of 17 patients and DRβ1*04 in some of the others, may have the ability to bind to several relevant T cell epitopes in the snRNP70 molecule. We have utilized a computer model to demonstrate that HLA II-restricted T cell epitopes present within the known autoantigens may be capable of eliciting an immune response. While other explanations and mechanisms exist, the authors suggest that epitope spreading may be one possible mechanism, amongst others, that may result in the simultaneous presence of two separate pathogenic autoantibodies.

Antiphospholipid syndrome plus rheumatic fever: a higher risk factor for stroke?

To compare clinical and laboratory findings between patients with primary antiphospholipid syndrome (PAPS) versus secondary APS due to rheumatic fever (APS-RF) (according to Jones criteria). Seventy-three APS patients (Sapporo criteria) were enrolled, and demographic, clinical, and laboratory data were collected. Exclusion criteria were heart congenital abnormalities and previous infectious endocarditis. Patients were divided into two groups: PAPS (n = 68) and APS-RF (n = 5). The mean current age, disease duration, frequencies of female gender, and Caucasian race were similar in APS-RF and PAPS patients (P > 0.05). Remarkably, the frequency of stroke was significantly higher in APS-RF compared to PAPS patients (80% vs. 25%, P = 0.02). Of note, echocardiogram of these patients did not show intracardiac thrombus. No significant differences were found in peripheral thromboembolic events (P = 1.0), pulmonary thromboembolism (P = 1.0), miscarriage (P = 0.16), thrombocytopenia (P = 0.36), arterial events (P = 0.58), and thrombosis of small vessels (P = 1.0). There were no differences in the frequencies of comorbidities such as diabetes mellitus, hypertension, smoking, and hyperlipidemia in both groups (P > 0.05). The frequencies of lupus anticoagulant, IgG, and IgM anticardiolipin were similar in two groups. APS patients associated with rheumatic fever without infective endocarditis may imply a high stroke risk as compared with PAPS, and future studies are needed to confirm this finding.

Potential role of molecular mimicry between human U1-70 kDa and fungal proteins in the development of T-cell mediated anti-U1-70 kDa autoimmunity

CONTEXT

Molecular mimicry between human and microbial antigens is a possible trigger of autoimmunity. The possible role of this mechanism in the onset of autoimmunity against the human autoantigen U1-70 kDa, typical of mixed connective tissue disease, is not fully elucidated.

OBJECTIVE

We aimed to identify microbial proteins highly similar to U1-70 kDa and potentially triggering anti-U1-70 kDa autoimmunity.

MATERIALS AND METHODS

We compared in silico the amino acid sequence of human U1-70 kDa and those of all the sequenced fungal, viral and bacterial proteins.

RESULTS

Human U1-70 kDa shares highly significant (E<10(-20)) amino acid sequence homology, spanning a segment containing T-cell epitopes, with 13 fungal (but no viral or bacterial) proteins, belonging to human pathogens. Nine of these proteins include the amino acid sequence VLVDVERGRTV, identical to the most frequent U1-70 kDa T-cell epitope in anti-U1-70 kDa positive patients, and sequences highly similar to the epitope DAFKTLFVARVN (identical residues or conservative residue substitutions in positions crucial for epitope binding).

DISCUSSION AND CONCLUSION

Cross-reactivity between human U1-70 kDa and microbial proteins was demonstrated for B-cell epitopes, but never investigated before for T-cell epitopes. Our data identify some fungal proteins as possible triggers of anti-U1-70 kDa autoimmunity via molecular mimicry. Research in this field could improve the understanding of the mechanisms leading to anti-U1-70 kDa autoimmunity, with potential consequences on prevention.

Immune pathogenesis of Mixed Connective Tissue Disease: a short analytical review

Mixed Connective Tissue Disease (MCTD) was first described 35 years ago by Gordon C. Sharp and his colleagues. In the ensuing decades, a clearer understanding of the clinical and serologic features of MCTD has emerged. Classification criteria now exist to define MCTD for study purposes, the long-term outcome of the disease has been established, and novel genetic associations within the major histocompatibility complex on chromosome 6 and select regions on chromosome 3 have been identified. Studies on immune pathogenesis have made substantial progress in advancing our understanding of MCTD. In MCTD, there is a complex interaction of the innate and adaptive immune system that culminates in autoimmune disease. Antigenic structural modification occurring during apoptosis or other modifications of self antigens leads to an autoantigen driven immune process with innate immune activation, immunoglobulin G autoantibody production directed against select components of the spliceosome, B lymphocyte activation, and CD4 and CD8 T lymphocyte participation.

Mixed connective tissue disease: what is behind the curtain?

Although there is still an emotional debate over the existence of mixed connective tissue disease, the evidence from animal models suggests that anti-U1RNP antibodies, similar to other autoantibodies in other connective tissue diseases (such as antisynthetase, anticentromere, and antitopoisomerase), play a pathophysiological role in this disease. Despite an antiendothelial effect of anti-U1RNP antibodies, which is reminiscent of anticentromere antibodies, patients with high-titer autoantibodies to U1RNP in the absence of anti-Sm antibodies do not usually have or develop typical systemic sclerosis. Instead, their severe Raynaud's syndrome is commonly accompanied by arthritis, which can be erosive, and by swollen/puffy hands and myositis. Pulmonary arterial hypertension is the major life-threatening complication in these patients and regular screening for this condition is essential.

Immunogenetic mechanisms for the coexistence of organ-specific and systemic autoimmune diseases

Background

Organ-specific autoimmune diseases affect particular targets in the body, whereas systemic diseases engage multiple organs. Both types of autoimmune diseases may coexist in the same patient, either sequentially or concurrently, sustained by the presence of autoantibodies directed against the corresponding autoantigens. Multiple factors, including those of immunological, genetic, endocrine and environmental origin, contribute to the above condition. Due to association of certain autoimmune disorders with HLA alleles, it has been intriguing to examine the immunogenetic basis for autoantigen presentation leading to the production of two or more autoantibodies, each distinctive of an organ-specific or systemic disease. This communication offers the explanation for shared autoimmunity as illustrated by organ-specific blistering diseases and the connective tissue disorders of systemic nature.

Presentation of the hypothesis

Several hypothetical mechanisms implicating HLA determinants, autoantigenic peptides, T cells, and B cells have been proposed to elucidate the process by which two autoimmune diseases are induced in the same individual. One of these scenarios, based on the assumption that the patient carries two disease-susceptible HLA genes, arises when a single T cell epitope of each autoantigen recognizes its HLA protein, leading to the generation of two types of autoreactive B cells, which produce autoantibodies. Another mechanism functioning whilst an epitope derived from either autoantigen binds each of the HLA determinants, resulting in the induction of both diseases by cross-presentation. Finally, two discrete epitopes originating from the same autoantigen may interact with each of the HLA specificities, eliciting the production of both types of autoantibodies.

Testing the hypothesis

Despite the lack of immediate or unequivocal experimental evidence supporting the present hypothesis, several approaches may secure a better understanding of shared autoimmunity. Among these are animal models expressing the transgenes of human disease-associated HLA determinants and T or B cell receptors, as well as in vitro binding studies employing purified HLA proteins, synthetic peptides, and cellular assays with antigen-presenting cells and patient's lymphocytes. Indisputably, a bioinformatics-based search for peptide motifs and the modeling of the conformation of bound autoantigenic peptides associated with their respective HLA alleles will reveal some of these important processes.

Implications of the hypothesis

The elucidation of HLA-restricted immune recognition mechanisms prompting the production of two or more disease-specific autoantibodies holds significant clinical ramifications and implications for the development of more effective treatment protocols.

A murine model of mixed connective tissue disease induced with U1 small nuclear RNP autoantigen

OBJECTIVE

To test whether immunizing mice with autoantigens closely linked to mixed connective tissue disease (MCTD) could induce an MCTD-like clinical syndrome distinguishable from systemic lupus erythematosus (SLE).

METHODS

Transgenic and knockout C57BL/6-derived mice were immunized subcutaneously at age 8-12 weeks with U1-70-kd small nuclear RNP (70K) fusion protein along with either Freund's complete adjuvant (CFA) or U1 RNA. After 2 months, mice were killed and analyzed histologically and serologically.

RESULTS

Immunization of C57BL/6-derived mice transgenic for human HLA-DR4 with 70K and either CFA or U1 RNA led to anti-70K antibodies in 62% of mice (21 of 34), and diversified anti-RNP immune responses. MCTD-like lung disease also developed in 50% of immunized mice (17 of 34), and anti-70K antibodies were strongly correlated with lung disease. CFA and U1 RNA were comparably able to induce this syndrome. Mice deficient in Toll-like receptor 3 (TLR-3) also developed this same syndrome when immunized with 70K and CFA. However, TLR-3(-/-) mice failed to develop MCTD-like lung disease when treated with 70K and U1 RNA. Rather, TLR-3(-/-) mice immunized with 70K and U1 RNA developed an autoimmune syndrome characterized by glomerulonephritis typical of SLE.

CONCLUSION

Exposure to 70K in an appropriate context is sufficient to induce autoimmunity and target organ injury consistent with MCTD. This system represents a new model of autoimmune interstitial lung disease, and establishes a closer link between anti-70K immunity and MCTD-like lung disease. Of note, changes in innate immune signaling can cause the same trigger to lead to the development of SLE-like nephritis rather than MCTD-like lung disease.

Autoantibodies in the Pathogenesis of Mixed Connective Tissue Disease

Antibodies to U1-RNP are part of the clinical definition of mixed connective tissue disease (MCTD). These antibodies and other well-defined antibodies tend to arise together in affected patients. Although still speculative, hypotheses that link U1-RNP antibodies to the development of autoimmunity in MCTD and that associate U1-RNP antibodies with mechanisms of tissue injury in MCTD have emerged and are being tested. Salient features of these hypotheses include: (1) an antigen-driven response that is due to impaired clearance of potentially immunogenic self-antigens, (2) inadequate B- and T-cell tolerance to RNP autoantigens, and (3) immunogenic properties of the RNA component of targeted ribonucleoproteins. Further studies are needed to establish whether anti-RNP antibodies have prognostic importance that is relevant to practicing clinicians.

Genetics and proteomics in scleroderma

The pathogenesis of systemic sclerosis (SSc; scleroderma) is still enigmatic. Genetic, familial, and twin studies suggest that SSc occurs in genetically susceptible individuals. Recent high-throughput technologies, including gene expression profiling and proteomics, have accelerated the rate of information acquired on possible mechanisms involved in SSc pathogenesis. The potential of the data obtained lies in their use for identifying new disease markers, monitoring disease activity, and developing tailored therapies. The result is an era of unprecedented advance that will benefit SSc and many other diseases.

Enfermedad mixta del tejido conjuntivo, conectivopatía indiferenciada y síndromes de superposición

Mixed connective tissue disease (MCTD), undifferentiated connective tissue disease and overlap syndromes are autoimmune systemic diseases that must be differentiated. Antibodies against the U1-ribonucleoprotein complex --spliceosome-- allows the diagnosis of mixed connective tissue disease. Links between the immunologic and clinical phenomena are emerging. Longitudinal studies of patients with MCTD highlight the impact of pulmonary hypertension and contribute to define the disease. Immunogenetic studies hold MCTD as an independent disease.

A Major B Cell Epitope Present on the Apoptotic but Not the Intact Form of the U1-70-kDa Ribonucleoprotein Autoantigen

Apoptotically modified forms of autoantigens have been hypothesized to participate in lupus immunopathogenesis. This study identifies a major B cell epitope present on the apoptotic but not the intact form of the U1-70-kDa ribonucleoprotein lupus autoantigen (70k). Human autoimmune sera with strong recognition of apoptotic 70k and minimal recognition of intact 70k were identified and tested for reactivity to truncated forms of 70k by immunoblot and ELISA. Patient sera that preferentially recognized apoptotic 70k were specific for an epitope dependent on residues 180-205 of the protein. This epitope was also recognized by 19 of 28 (68%) intact anti-70k-positive autoimmune human sera with Abs also recognizing apoptotic but not the intact form 70k, but only 1 of 9 (11%) intact 70k-positive sera without such Abs (Fisher's exact, p = 0.0055). Immunization of HLA-DR4-transgenic C57BL/6 mice with a peptide containing this epitope induced anti-70k immunity in 13 of 15 mice, including Abs recognizing apoptotic but not intact forms of autoantigens in 12 of 15 mice. Anti-70k responder mice also developed spreading of immunity to epitopes on the endogenous form of 70k, and proliferative lung lesions consistent with those described in patients with anti-70k autoimmunity. Thus, a major epitope in the B cell response to U1-70 kDa localizes to the RNA binding domain of the molecule, overlaps with the most common T cell epitope in the anti-70k response, and is not present on the intact form of the 70k molecule. Immunization of mice against this epitope induces an immune response with features seen in human anti-70k autoimmune disease.

T cell immunity in connective tissue disease patients targets the RNA binding domain of the U1-70kDa small nuclear ribonucleoprotein

Although the T cell dependence of autoimmune responses in connective tissue diseases has been well established, limited information exists regarding the T cell targeting of self Ags in humans. To characterize the T cell response to a connective tissue disease-associated autoantigen, this study generated T cell clones from patients using a set of peptides encompassing the entire linear sequence of the 70-kDa subunit of U1 snRNP (U1-70kDa) small nuclear ribonucleoprotein. Despite the ability of U1-70kDa to undergo multiple forms of Ag modification that have been correlated with distinct clinical disease phenotypes, a remarkably limited and consistent pattern of T cell targeting of U1-70kDa was observed. All tested T cell clones generated against U1-70kDa were specific for epitopes within the RNA binding domain (RBD) of the protein. High avidity binding of the RBD with U1-RNA was preserved with the disease-associated modified forms of U1-70kDa tested. The high avidity interaction between the U1-RBD on the polypeptide and U1-RNA may be critical in immune targeting of this region in autoimmunity. The T cell autoimmune response to U1-70kDa appears to have less diversity than is seen in the humoral response; and therefore, may be a favorable target for therapeutic intervention.

Lack of autoantibody production associated with cytomegalovirus infection

To confirm an association between cytomegalovirus (CMV) infection and the presence of antibodies to Smith (Sm), to ribonucleoprotein (RNP), and to a component of the U1 ribonucleoproteins (U1-70 kD), we measured antibodies to these protein antigens using an enzyme immunoassay and an immunoblot. The antibodies were measured in the sera of 80 healthy subjects, one-half of whom were naturally CMV seropositive and one-half were CMV seronegative, and in eight subjects immunized with a live attenuated strain of CMV. None of the vaccinees developed antibodies to Sm, to RNP, or to U1-70 kD at either 4 or 12 months after immunization. Additionally, there was no statistically significant association between levels of antibodies to Sm or to RNP and between sera obtained from vaccinees, natural CMV seropositive individuals, and CMV seronegative individuals. One CMV seropositive serum and one CMV seronegative serum tested positive for antibodies to U1-70 kD. These data indicate that neither wild-type infection nor the live-attenuated Towne vaccine frequently induce autoantibody production.

T cell epitope mapping of the Smith antigen reveals that highly conserved Smith antigen motifs are the dominant target of T cell immunity in systemic lupus erythematosus

B cell and T cell immunity to the Smith Ag (Sm) is a characteristic feature of systemic lupus erythematosus (SLE). We have shown that T cell immunity against Sm can be detected in SLE patients, and that T and B cell immunity against Sm are linked in vivo. TCR usage by Sm-reactive T cells is highly restricted and characteristic of an Ag-driven immune response. Sm is a well-characterized complex Ag consisting of proteins B1, B2, D1, D2, D3, E, F, and G. A unique feature of all Sm proteins is the presence of homologous motifs, Sm motif 1 and Sm motif 2. We used limiting dilution cloning and synthetic peptide Ags to characterize the human T cell immune response against Sm in seven SLE patients. We sought to determine the precise antigenic peptides recognized, the common features of antigenic structure recognized, and the evolution of the T cell response against Sm. We found there was a highly restricted set of Sm self-peptides recognized by T cells, with three epitopes on Sm-B and two epitopes on Sm-D. We found that T cell immunity against Sm-B and Sm-D was encoded within the highly conserved Sm motif 1 and Sm motif 2, and that immunity against these epitopes appeared stable. The present study supports the concept that T cell immunity to Sm is an Ag-driven immune response directed against a highly restricted set of self-peptides, encoded within Sm motif 1 and Sm motif 2, that is shared among all Sm proteins.

HLA antigens in Malay patients with systemic lupus erythematosus: association with clinical and autoantibody expression

BACKGROUND

Studies have shown that certain genes within the major histocompatibility complex predispose to systemic lupus erythematosus (SLE) and may influence clinical and autoantibody expression. Thus, we studied the frequency of HLA-DR, -DQA, -DQB and -DPB alleles in ethnic Malays with SLE to determine the role of these genes in determining disease susceptibility and their association with clinical and immunological manifestations.

METHODS

Fifty-six Malay SLE patients were enrolled into the study. Demographic, clinical and immunological findings were obtained from medical records. HLA-DR, DQ and DP typing were done using modified PCR-RELP. Controls were from ethnically-matched healthy individuals.

RESULTS

We found a strongly significant association of the DR2 and DQB1 *0501 and DQB1*0601 (pcorr = 0.03, rr = 3.83, pcorr = 0.0036, rr = 4.56 and pcorr = 0.0048 and rr = 6.0, respectively). There was also a weak increase of DQB1*0.201 and DPB1*0.0901 with a weak decrease of DQA1*0601 and DQB1*0503 and *0301 which were not significant after corrections for multiple comparisons were made. There was a significant positive association of DR2 and DQB1*0501 with renal involvement and DR8 with alopecia. A nonsignificant increase of DQB1*0503 in patients with photosensitivity was noted. Significant autoantibody associations were also found: DQB1*0601 with anti-Sm/RNP, DR2 with antiSSA (Ro)/SSB (La), and DR2, DQB1*0501 and *0601 with antibodies to ds DNA. There was no specific DR, DQ or DP associations with age of disease onset (below 30 years or those at or above 30 years).

CONCLUSION

Our data suggests the role of the HLA class II genes in conferring SLE susceptibility and in clinical and autoantibody expression.

Immunization with a bacterial ATP-binding cassette transporter fragment suppresses autoimmunity and prolongs survival in MRL/lpr lupus-prone mice

The present study was undertaken to better define the role of the U1 70 kDa antigen in a spontaneous murine model of systemic lupus erythematosus (SLE) by testing whether immunization with the U1 70 kDa polypeptide could alter the production of antibodies against U1 70 kDa or against other small nuclear ribonucleoproteins (snRNP), modify disease expression or alter survival. We found that, while immunization with a U1 70 kDa derived fusion protein (70 KFP) tended to delay the development of anti-snRNP antibodies in the sera of MRL/lpr mice, it had no effect on autoimmune-mediated renal disease or survival. Unexpectedly, it was found that MRL/lpr mice immunized with a 367 amino acid fragment of a bacterial ATP-binding cassette transporter, MFP, had prolonged survival compared to saline injection or U1 70 kDa immunization and that this was associated with a delay in the onset of SLE-like proliferative glomerulonephritis. This is the first study, to our knowledge, in which a bacterial ATP-binding cassette transporter was shown to be beneficial in treating a murine model of SLE. We report that MFP significantly prolonged longevity in the MRL/lpr murine model of SLE compared to saline injection or 70 KFP immunization and that improved survival was associated with a delay in the onset of SLE-like glomerulonephritis.

Mixed connective tissue disease: overlap syndromes

Since the original description of mixed connective tissue disease (MCTD) as an apparently unique syndrome by Sharp and co-workers, the concept of MCTD has been highly controversial. In this chapter, a quarter of a decade later, we examine the evidence that MCTD is a distinctive entity rather than a haphazard association of clinical and serological features and that the presence of high titres of autoantibodies to UIRNP influences the expression of connective tissue disease in ways that are relevant to prognosis and treatment. Results of longterm clinical studies are presented, which show that the clinical phenotype of MCTD is robust and can be defined by classification criteria that show reasonable sensitivity and specificity. In addition, the chapter addresses the results of immunogenetic and serological studies that demonstrate that MCTD is quite distinctive from systemic lupus erythematosus and systemic sclerosis. Indeed, there is good evidence that the clinical and serological features of MCTD are not just a haphazard association but that these patients represent a distinctive subset of connective tissue disease in which the specific autoimmune response is relevant to clinical expression and to understanding the underlying pathogenesis.

Scleroderma overlap syndromes

The most common scleroderma overlap syndromes are mixed connective tissue disease (MCTD), scleromyositis and synthetase syndrome. There is controversy concerning MCTD as a separate entity due to heterogeneous clinical manifestations, not infrequent transformation into definite CTD and various classification criteria. Our study of 94 adult patients and 20 children, classified according to the criteria of Alarcon-Segovia, and especially a 5, 9-year follow-up showed transformation into SLE or SSc in over 20% of patients, less frequently than reported by others, whereas over half of the cases remained undifferentiated CTD. In several cases ARA criteria for both SSc and SLE were fulfilled, and there is no consensus whether such cases should be recognized as coexistence of both definite diseases or as MCTD. High titers of U1 RNP antibodies to 70 kD epitope were invariably present, whereas, by transformation into distinctive CTD there appeared, in addition, antibodies characteristic of these CTD. Of 108 cases positive for PM-Scl antibody, 83% were associated with scleromyositis. This scleroderma overlap syndrome differed from MCTD by coexistent features of dermatomyositis (myalgia, myositis, Gottron sign, heliotrope rash, calcinosis) with no component of SLE, characteristic of MCTD. The course was also chronic and rather benign, as in MCTD, and all cases responded to low or moderate doses of corticosteroids. A not infrequent complication was deforming arthritis of the hands. Our immunogenetic study showed an association of cases positive for PM-Scl antibody with HLA-DQA1x0501 alleles in 100% and with HLA-DRB1x0301 in 94% of cases. Synthetase syndrome, associated with anti-histidyl-tRNA synthetase antibodies, studied in 29 patients with myositis and interstitial lung disease (ILD), only in single cases had scleroderma-like features. These cases differed from SSc by acute onset with fever, and by response to moderate doses of corticosteroids. We also studied overlap of localized scleroderma with other CTD: 21 cases of progressive facial hemiatrophy and linear scleroderma, and 55 (39.5%) of atrophoderma Pasini-Pierini (APP) and morphea. As in other autoimmune disorders, two or more connective tissue diseases (CTD) may develop concurrently or sequentially in the same patient. In such overlap syndromes ARA criteria must be fulfilled for each of the disease, and the clinical presentation has features of both. However more frequently overlap syndromes only combine some manifestations of more than one CTD, and present a highly heterogeneous group of disorders with prevailing clinical features of SSc.

Long-term outcome in mixed connective tissue disease: longitudinal clinical and serologic findings

OBJECTIVE

To determine the long-term clinical and immunologic outcomes in a well-characterized cohort of 47 patients with mixed connective tissue disease (MCTD), including reactivity with U small nuclear RNP (snRNP) polypeptides.

METHODS

Patients were followed up over a period of 3-29 years with immunogenetic and systematic clinical and serologic analysis. Sera were analyzed for reactivity with snRNP polypeptides U1-70 kd, A, C, B/B', and D, for anti-U1 RNA, and for anticardiolipin antibodies (aCL).

RESULTS

The typical core clinical features of MCTD tended to develop over time; features of inflammation as well as Raynaud's phenomenon and esophageal hypomotility diminished, while pulmonary hypertension, pulmonary dysfunction, and central nervous system disease persisted, following treatment. A favorable outcome was observed in 62% of patients; 38% had continued active disease or had died, with death associated with pulmonary hypertension and aCL. All patients had autoantibodies to the U1-70 kd polypeptide of snRNP, and most were positive for anti-U1 RNA. An orderly progression of intramolecular spreading of autoantibody reactivity against snRNP polypeptides was observed, as was the novel finding of "epitope contraction" followed by disappearance of anti-snRNP autoantibodies during prolonged remission.

CONCLUSION

These patients demonstrated the typical immunogenetic, clinical, and serologic findings of MCTD, and the condition rarely evolved into systemic lupus erythematosus or systemic sclerosis. The majority of patients had favorable outcomes, with pulmonary hypertension being the most frequent disease-associated cause of death. Intramolecular spreading of autoantibody reactivity against snRNP polypeptides was observed, followed by "epitope contraction" and ultimate disappearance of anti-snRNP autoantibodies during prolonged disease remission.

Long-term outcome in mixed connective tissue disease: longitudinal clinical and serologic findings

OBJECTIVE

To determine the long-term clinical and immunologic outcomes in a well-characterized cohort of 47 patients with mixed connective tissue disease (MCTD), including reactivity with U small nuclear RNP (snRNP) polypeptides.

METHODS

Patients were followed up over a period of 3-29 years with immunogenetic and systematic clinical and serologic analysis. Sera were analyzed for reactivity with snRNP polypeptides U1-70 kd, A, C, B/B', and D, for anti-U1 RNA, and for anticardiolipin antibodies (aCL).

RESULTS

The typical core clinical features of MCTD tended to develop over time; features of inflammation as well as Raynaud's phenomenon and esophageal hypomotility diminished, while pulmonary hypertension, pulmonary dysfunction, and central nervous system disease persisted, following treatment. A favorable outcome was observed in 62% of patients; 38% had continued active disease or had died, with death associated with pulmonary hypertension and aCL. All patients had autoantibodies to the U1-70 kd polypeptide of snRNP, and most were positive for anti-U1 RNA. An orderly progression of intramolecular spreading of autoantibody reactivity against snRNP polypeptides was observed, as was the novel finding of "epitope contraction" followed by disappearance of anti-snRNP autoantibodies during prolonged remission.

CONCLUSION

These patients demonstrated the typical immunogenetic, clinical, and serologic findings of MCTD, and the condition rarely evolved into systemic lupus erythematosus or systemic sclerosis. The majority of patients had favorable outcomes, with pulmonary hypertension being the most frequent disease-associated cause of death. Intramolecular spreading of autoantibody reactivity against snRNP polypeptides was observed, followed by "epitope contraction" and ultimate disappearance of anti-snRNP autoantibodies during prolonged disease remission.

T cell receptor beta-chain third complementarity-determining region gene usage is highly restricted among Sm-B autoantigen-specific human T cell clones derived from patients with connective tissue disease

OBJECTIVE

To determine the structure of T cell receptors (TCR) used by Sm-B-reactive human T cell clones, to map T cell epitopes on the Sm-B autoantigen, and to determine the HLA restriction element used in the recognition of Sm-B by T cells.

METHODS

Sm-B-reactive T cell clones were generated from patients with connective tissue disease by using either a recombinant fusion protein or synthetic peptides. The TCR structure was defined with the use of polymerase chain reaction and DNA sequencing. Synthetic peptides were used to map T cell epitopes on Sm-B. HLA restriction element usage was defined by using monoclonal antibody blocking.

RESULTS

Usage of the TCR third complementarity-determining region (CDR3) was highly restricted among Sm-B autoantigen-specific human T cell clones. Only amino acids 48-96 of the Sm-B2 autoantigen were recognized by T cells, and this occurred in the context of HLA-DR.

CONCLUSION

TCR CDR3 gene usage is highly conserved by Sm-B autoantigen-specific T cell clones, and this appears to be related to the recognition of a limited number of T cell epitopes on the Sm-B autoantigen presented in the context of HLA-DR.

Analysis of T cell receptors specific for U1-70kD small nuclear ribonucleoprotein autoantigen: the alpha chain complementarity determining region three is highly conserved among connective tissue disease patients

The U1-70kD autoantigen is a major target of B cell responses in patients with connective tissue diseases (CTD). T cell responses are important in the pathogenesis of CTD, however little is known about autoantigen-specific T cells in these diseases. We have recently proven that U1-70kD-reactive human T cells exist. To further characterize these autoreactive T cells, U1-70kD-reactive T cell clones have been generated from patients with CTD using either a recombinant fusion protein or synthetic peptides spanning the U1-70kD polypeptide. T cell receptors (TCR) isolated from the U1-70kD-reactive T cell clones were sequenced and the third complementarity-determining region (CDR3) compared to determine if a common motif was present. mAb blocking of antigen-induced proliferation was done to determine the HLA restriction element used in recognition of the U1-70kD autoantigen by T cells. The results presented here indicate that TCRAV CDR3 usage is highly restricted among U1-70kD autoantigen-specific human T cells clones derived from CTD patients with distinctive structural features. Furthermore, the recognition of the U1-70kD autoantigen occurs in the context of HLA-DR.

Analysis of autoantibodies against RNA polymerases using immunoaffinity-purifed RNA polymerase I, II, and III antigen in an enzyme-linked immunosorbent assay

Autoantibodies against RNA polymerases (RNAP) have been reported to occur in patients with a wide variety of connective tissue diseases (CTD), including systemic sclerosis (SSc), systemic lupus erythematosus (SLE), and mixed connective tissue disease (MCTD). The frequency of anti-RNAP antibodies has been reported to vary widely between different CTD diseases in studies examining different patient populations. Furthermore, these studies have been limited by the fact that methods have not previously been available for detecting antibodies against RNAP which are both rapid and quantitative. We have developed an enzyme-linked immunosorbent assay (ELISA) for rapidly quantitating antibodies against RNAP I, II, and III. We have utilized both the ELISA and the immunoprecipitation of 35S-labeled HeLa cells to analyze sera from a large cohort of well-characterized Caucasian CTD patients for the presence of anti-RNAP antibodies. We found excellent concordance for the presence of anti-RNAP antibodies using immunoprecipitation and ELISA. Anti-RNAP antibodies occurred predominantly among female patients with the diffuse form of SSc and were detected in 8/36 (22%) of Caucasian patients with diffuse SSc and 1/53 (2%) with limited SSc. Anti-RNAP antibodies occurred in 1/42 (2%) of patients with SLE. Anti-RNAP antibodies did not occur in MCTD (0/49). Antibodies against RNAP were rare among antinucleolar-reactive sera, occurring in only 3/200 (1.5%). The RNAP ELISA provides a validated method which can be rapidly utilized in a clinical diagnostic laboratory setting to identify SSc patients who are at risk for developing diffuse SSc with multiorgan involvement and hypertensive renal crisis.

Clinical correlates, serum autoantibodies and the role of the major histocompatibility complex in French Canadian and non-French Canadian Caucasians with SLE

OBJECTIVE

To investigate the predisposing role of major histocompatibility complex (MHC) genes to autoantibody production and clinical manifestations comparing French Canadian and Non-French Canadian Caucasians with systemic lupus erythematosus (SLE) METHODS: Ninety-one Caucasian patients with SLE were studied. Clinical manifestations, autoantibody expression and HLA-A, B, (serology), DR, DQ and C4A gene deletion (restriction fragment length polymorphism [RFLP] typing) were determined.

RESULTS

Photosensitivity was present in all SLE subjects with anti-Ro antibodies (P=0.001, RR=13.1, CI=1.8, 564). Photosensitivity was further associated with the HLA-A1, C4A gene deletion haplotype. More strikingly, C4A gene deletion was associated with anti-Ro (P=0.008, RR=4.6, CI=1.4, 16.2) and anti-La (P=0.02, RR=11.7, CI=1.4, 549) autoantibodies. This relationship was also significant for anti-Ro antibody in the French Canadian patients (P=0.01, RR=21.3, CI=1.7, 105.3). In contrast, anti-dsDNA autoantibodies were negatively associated with photosensitivity (P=0.02, RR=0.3, CI=0.07, 0.8) and correlated with HLA-DR15 (P=0.006, RR=4.2, CI=1.5, 12.8) and Dw2 (P=0.009, RR=3.9, CI=1.4, 11.9).

CONCLUSION

C4A gene deletion has a previously unrecognized powerful association with anti-Ro and anti-La autoantibodies. These results support the concept of divergent MHC gene associations with autoantibody expression and emphasize the influence of ethnicity on the immunogenetic study of SLE.

Course of mixed connective tissue disease in children

Mixed connective tissue disease (MCTD) was first reported 25 years ago. This report provides an assessment of the course of juvenile (J) MCTD in 224 patients available in the literature until 1996, including our own 33 patients. Most patients improved and remissions were observed in 3-5% (up to 27%). Among the long-term problems, a loss in joint function was seen in up to 29% of the cases, renal involvement in up to 47%, restrictive lung disease in up to 54% and gastrointestinal manifestations consisting of oesophageal dysmotility in up to 29%. Cerebral involvement was rare but severe. Cardiovascular problems observed include cardiomyopathy, myopericarditis and pulmonary hypertension. Among other long-term problems were Raynaud's phenomenon and scleroderma-like skin changes in up to 86% of the patients. Seventeen of the 224 patients had died (7.6%) because of sepsis or infection (7), cerebral complications (3), heart failure (2), pulmonary hypertension (2), renal failure (2) or gastrointestinal bleeding (1). The mortality rate of JMCTD seems to be in the same range as that of juvenile systemic lupus erythematosus, dermatomyositis and scleroderma. When compared with the other connective tissue diseases, however, mainly minor long-term problems are seen in the surviving patients.

Analysis of human T cell and B cell responses against U small nuclear ribonucleoprotein 70-kd, B, and D polypeptides among patients with systemic lupus erythematosus and mixed connective tissue disease

OBJECTIVE

To analyze T and B cell reactivity with U small nuclear RNP (snRNP) 70-kd, B, and D polypeptides among patients with connective tissue disease (CTD) and to examine the functional characteristics of snRNP-reactive T cell clones.

METHODS

We used an snRNP enzyme-linked immunosorbent assay and immunoblotting to characterize antibodies in patients' sera. We used human recombinant fusion proteins 70 kd, B, and D to stimulate and clone snRNP-reactive T cells from CTD patients. We analyzed the cell surface phenotype, antigenic specificity, and cytokine profiles of T cell clones.

RESULTS

Patients showed T cell responsiveness to snRNP polypeptides that paralleled their autoantibody reactivities. A total of 256 clones were generated, and clones were identified which were specific for the 70-kd, B, or D polypeptides. Clones expressed a T helper cell phenotype, and were found to produce substantial quantities of both interleukin-4 (IL-4) and interferon-gamma, and lesser quantities of IL-2 and IL-6.

CONCLUSION

These results show that CTD patients have clonable circulating snRNP-reactive T cells that parallel the specificity of snRNP-reactive antibodies in their sera. The snRNP-reactive T cells exhibit a helper cell phenotype and produce cytokines which are important in B cell help and differentiation.

Blotting patterns of IgG anti-(U1)RNP antibodies in mixed connective tissue disease

Serum reactivities towards individual U1 snRNP proteins were determined by immunoblotting in 32 patients with mixed connective tissue disease (MCTD). Time persistence of immunoblot profiles and clinical significance of anti-(U1)RNP antibody specificities were also investigated. IgG anti-(U1)RNP antibodies were found in the sera of 29 out of 32 patients (90.6%): 21 (65.6%) reacted with the 70-kD protein, 25 (78.1%) with A, 23 (71.9%) with C and 20 (62.5%) with B/B' proteins. None were reactive with the Sm-D peptide. Seventy kilodalton antibody specificity was strongly associated with a higher antinuclear antibody titre (> 160) and slightly associated with disease activity; anti-B/B' specificity was associated with lymphadenopathy. Anti-A, -C and -B/B' antibodies were negatively associated with systemic lupus erythematosus (SLE) skin rashes. Two types of anti-(U1)RNP blotting patterns were selected: "full spectrum" (53.1% of cases) and a "partially/no reactive" one (46.9%). Such patterns were unchanged over time in 14 out of 16 cases prospectively examined (87.5%), while the pattern shifted from "full spectrum" to "partially/no reactive" in 2 cases (12.5%): in 1 after a prolonged clinical remission (> or = 4 years) and in the other following immunosuppressive therapy. The anti-(U1)RNP antibody immunoblot profile in MCTD patients consisted of various reactivities and remained unchanged over time in most cases. Antibody reactivity against the 70-kD protein represented the major U1 snRNP specificity. The various anti-(U1)RNP specific reactivities demonstrated poor clinical significance within MCTD. Thus, MCTD seems to be characterized by a longstanding serological heterogeneity whose reactivities do not apparently correspond to distinct features within the broad clinical spectrum of MCTD.

Long term follow-up of children with mixed connective tissue disease

Mixed connective tissue disease (MCTD) is characterized by features of more than one of the rheumatic disorders with antinuclear antibodies in a speckled pattern and with antibodies to nuclear ribonucleoprotein (nRNP). MCTD is uncommon in children and long-term follow-up studies in children are infrequently reported. A retrospective review of clinical experience at five pediatric rheumatology centers provided 11 patients who met the following inclusion criteria: (1) Kasukawa's criteria for MCTD1; (2) presentation younger than 18th birthday; (3) greater than five years of follow-up; (4) completion of data collection form. The widely varying outcomes of these 11 children with MCTD on long-term follow-up may lend doubt that this is a unique and distinctive rheumatologic disorder.

Clinical correlations with HLA type in Japanese patients with connective tissue disease and anti-U1 small nuclear RNP antibodies

OBJECTIVE

To elucidate the roles of HLA genes in the clinical presentation of patients with connective tissue disease and serum anti-U1 small nuclear RNP antibody.

METHODS

HLA class I antigens and HLA class II alleles were determined in 43 Japanese patients with anti-U1 RNP antibody alone, by microcytotoxicity testing and DNA typing, respectively. Prospectively recorded clinical and laboratory features were analyzed in relation to HLA class I and class II types.

RESULTS

DQB1*0303 was associated with lupus-related symptoms including fever, malar rash, oral ulcers, hypocomplementemia, and high-titer anti-double-stranded DNA antibody. Other HLA-clinical associations included DR2 with pleuritis, DR4 with hand swelling, and DRB1*0405 with arthritis.

CONCLUSION

These HLA-clinical associations explain, in part, the heterogeneous clinical presentation in patients with anti-U1 RNP antibody.

Association between polymorphisms in the TNF region and systemic lupus erythematosus in the Italian population

The purpose of this work was to the hypothesis that MHC encoded susceptibility factors for SLE lie in the TNF region. An association study was performed by analyzing 123 northern Italian SLE patients and 199 matched controls for three TNF markers: two polymorphisms in the TNFA promoter and the TNFa microsatellite. Haplotypic combinations of TNF markers were also compared in patients and controls. No significant association was observed considering either the whole SLE panel or SLE clinical and immunological subtypes. Three TNF-238/A homozygous patients were detected, while no homozygote was present in controls. The clinical and immunological phenotype of the three -238/A homozygotes suggests that the -238/AA genotype is a marker of a particular clinical subtype.

Analysis of anti-U1 RNA antibodies in patients with connective tissue disease. Association with HLA and clinical manifestations of disease

OBJECTIVE

To determine the prevalence of anti-U1 RNA antibodies in connective tissue disease (CTD) patients and evaluate immunogenetic and clinical features of patients possessing these antibodies.

METHODS

RNA immunoprecipitation was used to analyze patient and healthy control sera for the presence of anti-R1 RNA antibodies. Enzyme-linked immunosorbent assay and immunoblotting were used to determine small nuclear RNP (snRNP) polypeptide antibodies. HLA polymorphisms were determined by microcytotoxicity and DNA typing.

RESULTS

Anti-U1 RNA IgM and IgG antibodies were found in 60% of anti-RNP positive patients. All of the anti-U1 RNA positive patients had anti-70K, and most had anti-A, (U1)snRNP polypeptide antibodies. HLA-DR2/DR4, as well as Raynaud's phenomenon and synovitis, were significantly increased in the anti-U1 RNA positive group.

CONCLUSION

The presence of anti-U1 RNA antibodies correlates with anti-70K and anti-A polypeptide antibodies. In addition, the anti-U1 RNA positive CTD patient group is immunogenetically and clinically distinctive from the anti-U1 RNA negative patient group.

T cell lines recognizing the 70-kD protein of U1 small nuclear ribonucleoprotein (U1snRNP)

In sera of patients with mixed connective tissue disease (MCTD) high titres of IgG autoantibodies to U1snRNP-specific proteins (70 kD, A, C) are found, suggesting an antigen-driven and T-cell-dependent process. In order to establish U1snRNP-specific T cell lines we cultured under various culture conditions mononuclear cells from MCTD patients and healthy donors with a highly purified UsnRNP preparation from HeLa cells. Nine T cell lines were established by limiting dilution cloning from two MCTD patients and five T cell lines from a healthy individual. All T cell lines expressed the TCR alpha beta/CD3 complex. Surprisingly, most of the T cells lines exhibited the CD8 phenotype. Irrespective of this phenotype, all T cell lines showed a proliferative response to an N-terminal part (aa 51-195) of recombinant U1-specific 70-kD protein. One CD8+ T cell clone exhibited cytotoxic activity against an autologous B cell line pulsed with snRNP or recombinant fragments (aa 51-95 and aa 51-88). Interestingly, two T cell lines proliferated in response to four recombinant polypeptides representing different parts of the U1snRNP 70-kD protein. Since regions of sequence homology are distributed over the 70-kD molecule, it is suggested that conserved motifs may be recognized by the T cell lines.

Neonatal lupus erythematosus: discordant disease expression of U1RNP-positive antibodies in fraternal twins--is this a subset of neonatal lupus erythematosus or a new distinct syndrome?

Neonatal lupus erythematosus (NLE) is an uncommon disease that is manifested by cutaneous lesions, cardiac conduction defects, or both, that appear in utero or shortly after birth. In approximately 95% of patients, anti-Ro antibody (Ro[SS-A]) has been identified and has become the serologic marker for NLE. Since 1987 there have been four reported cases of Ro- and anti-La antibody (La[SS-B])-negative, U1RNP antibody-positive, NLE. Our affected twin, as well as all other infants with U1RNP-positive NLE, had cutaneous lesions similar to those in Ro-positive NLE, although they lacked systemic abnormalities, including cardiac conduction defects. HLA typing of mothers with infants with U1RNP-positive NLE revealed the presence of HLA-DR4, DQw1, or DQw3 phenotypes. Our typing confirms these findings. As with Ro-positive NLE, no distinct HLA associations were demonstrated in the infants. Unlike Ro-positive mothers, all mothers with a U1RNP-positive infant with NLE had connective tissue disease at the time of the diagnosis and had a different spectrum of disease. We describe the clinical, serologic, and immunogenetic findings in the first reported case of U1RNP-positive NLE in dizygotic twins in whom the NLE disease expression was discordant.

Autoantibodies in the diagnosis of systemic rheumatic diseases

Distinct profiles of autoantibodies directed to intracellular antigens can be detected in the systemic connective tissue diseases. They aid in establishing the correct diagnosis and are included in many sets of diagnostic criteria, such as the ones developed for systemic lupus erythematosus (anti-Smith antigen and anti-double-strand DNA antibodies), mixed connective tissue disease (anti-U1-nuclear ribonucleoprotein antibodies), and Sjögren's syndrome (SS) (anti-SS-A/Ro and anti-SS-B/La antibodies). They are useful prognostic markers in some situations and facilitate clinical and treatment follow-up. Autoantibodies have also been used as probes to gain insights into cell biology, helping to isolate and purify intracellular proteins involved in key cellular functions. We give detailed information on two of the most useful techniques for the detection of autoantibodies in the clinical and research laboratory settings, indirect immunofluorescence and immunoblotting. We also discuss several of the antigen-autoantibody systems found in systemic lupus erythematosus (Smith antigen, U1-nuclear ribonucleoprotein, SS-A/Ro, SS-B/La, proliferating cell nuclear antigen ribosomal ribonucleoprotein, double-strand DNA, histones, antiphospholipids, Ku, Ki/SL), systemic sclerosis (centromere, topo I, RNA polymerases, fibrillarin, polymyositis-Scl, Th/To), polymyositis/dermatomyositis (transferRNA synthetases, signal recognition particle, and others), and SS (SS-A/Ro, SS-B/La, nucleolar organizing region-90, p80-coilin), addressing their clinical significance, common detection methods, immunogenetic associations, and the molecular and cellular biology of the cognate antigens.

Major histocompatibility complex class II gene associations with anti-U1 small nuclear ribonucleoprotein antibody. Relationship to immunoreactivity with individual constituent proteins

OBJECTIVE

To better define immunogenetic associations with the anti-U1 ribonucleoprotein (U1 RNP) autoantibody response.

METHODS

HLA class II alleles were determined by genotyping in 49 Japanese rheumatic disease patients with anti-U1 RNP antibody and 43 race-matched healthy controls. Immunoreactivities to U1 RNP constituent proteins (70K, A, B/B', and C) were detected by immunoblots using purified HeLa cell Sm antigen, and antibody titer was determined by passive hemagglutination assay.

RESULTS

DQB1*0302 was significantly more frequent in anti-U1 RNP-positive patients than in controls (43% versus 14%; odds ratio [OR] = 4.6, corrected P = 0.03). All anti-U1 RNP-positive patients had either a DQB1*0601, *0602, *0301, *0302, or *0303 allele, which share tyrosine at position 30, and the amino acid sequence Thr, Arg, Ala, Glu, Leu, Asp, and Thr at positions 71-77 in the DQB1 beta 1 domain. In contrast, one of these alleles was found in 81% of the controls (OR = 24, P = 0.002). In addition, anti-U1 RNP antibody was associated with unique DQB1*0302; DRB1*0401 haplotype. Anti-70K reactivity and antibody titer were positively associated with a basic amino acid residue, arginine or histidine, at position 13 (DR2 or DR4) and were negatively associated with the amino acid sequence Ile, Leu, Glu, and Asp at positions 67-70, which was present in some of the DR5-, DR6-, and DR8-associated alleles, in the DRB1 beta 1 domain. Anti-C reactivity was strongly associated with DR2, particularly with DRB1*1502.

CONCLUSION

The several shared epitopes located on HLA-DRB1 and DQB1 genes control the anti-U1 RNP autoantibody response.

HLA type as a predictor of mixed connective tissue disease differentiation. Ten-year clinical and immunogenetic followup of 46 patients

OBJECTIVE

To determine any clinical or genetic markers of differentiation and outcome in a previously described cohort of 46 patients with mixed connective tissue disease (MCTD).

METHODS

Patients were clinically evaluated, chart notes reviewed, and HLA subtyping and immunology profiles performed where possible. Eleven had died and 7 were lost to followup.

RESULTS

MCTD had differentiated into systemic lupus erythematosus in 12 patients and into systemic sclerosis in 13. The latter was associated with HLA-DR5 (P = 0.038), and nondifferentiation was associated with HLA-DR2 or DR4 (P = 0.007). Three HLA-DR4 positive patients had MCTD that evolved into rheumatoid arthritis. Erosive and/or deforming arthritis was associated with HLA-DR1 or DR4 (P = 0.015). HLA-DR3 was associated with interstitial lung fibrosis (P = 0.044) and keratoconjunctivitis sicca (0.001 < P < 0.01). Severe Raynaud's phenomenon predicted higher mortality (0.01 < P < 0.05).

CONCLUSION

We suggest that MCTD is, for most patients, an intermediate stage in a genetically determined progression to a recognized connective tissue disease. Those whose disease remains undifferentiated might be considered a distinct subset.

HLA class II genes and antibodies against recombinant U1-nRNP proteins in patients with systemic lupus erythematosus. SLE Study Group

To investigate a possible involvement of HLA-class II alleles in the genetic predisposition for the formation of anti-U1-nRNP antibody-in systemic lupus erythematosus (SLE), genomic DNA of 178 patients was typed for the DRB1, DQA1 and DQB1 alleles using a polymerase chain reaction (PCR) and non-radioactive-oligonucleotide typing. Antibodies against recombinant U1-nRNP proteins (U1-A-, U1-C- and 70K-protein) were determined by ELISA. Anti-U1-C antibody was found in 26 (14.7%), anti-U1-A in 34 (19.2%) and anti-70K in 17 (9.6%) patients. A joint occurrence was observed for these antibodies against the recombinant U1-nRNP proteins: anti-U1-C and anti-U1-A antibodies occurred together more frequently than alone and than together with anti-U1-70K antibodies. The frequency of DRB1*04 was slightly increased in the patients with anti-U1-C as compared to the patients without anti-U1-C (P < 0.05, Pcorr = n.s., RR = 2.4). The DQA1*0301 allele, which is in linkage disequilibrium with DRB1*04, is found more frequently in anti-U1-C-positive than in antibody-negative patients. The DQB1*0303 allele, detected in 12 of 176 SLE patients, was absent in the patients with any of the antibodies against the U1-nRNP proteins. All these deviations may be due to chance alone. We concluded that the presence of antibodies against recombinant U1-nRNP proteins was not significantly associated with any HLA DRB1, DQA1 and DQB1 allele in our group of SLE patients.

Racial differences in the distribution of systemic sclerosis-related serum antinuclear antibodies

OBJECTIVE

To determine racial differences in the frequencies of systemic sclerosis (SSc)-related serum antinuclear antibodies (ANA).

METHODS

We tested serum samples from 275 Japanese, 416 North American Caucasian, and 24 North American black SSc patients for 8 SSc-related serum ANA, using indirect immunofluorescence, double immunodiffusion, and radioimmunoprecipitation assays.

RESULTS

In comparing the 3 racial groups, we found that anti-U1 RNP, anti-RNA polymerase I, II, and III, and anti-U3 RNP antibodies were the most frequently detected antibodies in Japanese, Caucasian, and black patients, respectively. Anti-PM-Scl antibody was found exclusively in Caucasians.

CONCLUSION

The production of SSc-related serum ANA is related to immunogenetic background.