Circulating Anti-Nuclear Antibodies in Systemic Sclerosis: Diagnosis and Subsetting, Monografías, Ensayos de Reumatología

¡Descarga Circulating Anti-Nuclear Antibodies in Systemic Sclerosis: Diagnosis and Subsetting y más Monografías, Ensayos en PDF de Reumatología solo en Docsity! —Review— Circulating Anti-Nuclear Antibodies in Systemic Sclerosis: Utility in Diagnosis and Disease Subsetting Masataka Kuwana Department of Allergy and Rheumatology, Nippon Medical School, Tokyo, Japan The presence of circulating anti-nuclear antibodies (ANA) is a hallmark of immune dysregulation in patients with systemic sclerosis (SSc). Currently, a variety of SSe-specific ANAs, including anticen- tromere, anti-topoisomerase 1, and anti-RNA polymerase III antibodies, have been well characterized, and their commercial kits are available worldwide. Since these autoantibodies are specifically detected in Sc patients and are associated with unique sets of disease manifestations, they are widely used in routine clinical practice for diagnosis, clinical subgrouping, and prediction of future organ involvements and prognosis. In addition, SSc-specific ANAS are also useful in predicting future development of SSc in patients with Raynaud's phenomenon without any scleroderma skin changes, because their produc- tion often precedes onset of SSc symptoms. Application of circulating SSc-specific ANA measurement to clinical practice has greatly improved patient care, but utility of the autoantibody testing could be maxi- mized by combining other clinical information, such as degree and extent of skin thickness and disease duration. (| Nippon Med Sch 2017; 84: 56-63) Key words: anti-nuclear antibody, biomarker, diagnosis, scleroderma, systemic sclerosis Introduction Systemic sclerosis (SSc) or scleroderma is a connective tissue disease characterized by excessive fibrosis, mi- croangiopathy, and immune dysregulation, including autoimmunity and chronic low-grade inflammation'. Multiple genes contribute to disease susceptibility, but environmental exposures are likely to play a major role in causing and progressing the disease. Since clinical presentation in patients with SSc is highly variable, dis- ease subgrouping as well as prediction of future organ involvement and prognosis are extremely important in clinical setting. One of the distinctive hallmarks of the immune dysregulation is the presence of circulating autoantibodies reactive with various cellular components. The majority of disease-associated autoantibodies in SSc patients are anti-nuclear antibodies (ANAs) that target proteins that play essential roles in transcription, splic- ing, and cell division. It has been shown that ANA speci- ficities specifically detected in SSc patients are associated with unique disease manifestations. Therefore, individual ANASs are attractive biomarkers in routine rheumatology practice. This review features the spectrum of SSe-specific ANAs and their clinical utility. SSc-specific and SSc-related ANAs ANAs detected by indirect immunofluorescence (IF) technique are a hallmark of SSc, and are found in >95% of the patients. The majority of nuclear autoantigens rec- ognized by SSc sera have been already identified to date. ANAs detected in SSc sera can be divided into two groups, including SSc-specific ANAs, which are specifi- cally detected in SSc patients, and SSc-associated ANAs, which are found in patients with SSc but also in those with non-SSc connective tissue diseases. Currently, at least 10 ANA specificities specific to SSc have been re- ported and well characterized. These include anticen- tromere, anti-topoisomerase 1 (topo D), anti-RNA polym- erase (RNAP) III, anti-U3 ribonucleoprotein (RNP), anti- Th/To, anti-Ul1/U12 RNP, anti-PM-Sel, anti-Ku, anti- RuvBL1/2, anti-Ul RNP antibodies. These SSc-specific ANAs are detectable in >80% of Sc patients. Two classic autoantibodies discovered in the late 1970's are anti-topo Correspondence to Masataka Kuwana, MD, PhD, Department of Allergy and Rheumatology, Nippon Medical School, 1-15 Sendagi, Bunkyo-ku, Tokyo 113-8602, Japan E-mail: kuwanamOnms ac jp Journal Website (http: / /www2.nms.acp /jnms/) 56 ] Nippon Med Sch 2017; 84 (2) Anti-Nuclear Antibodies in Scleroderma Table 1 Staining patterns on IIF and clinical correlation of SSc-specific ANAs ANA specificity Staining pattern on IIF Disease subset Organ manifestations Anticentromere Discrete speckled LeSSc PAH, DU in late disease (ACA) Anti-topo 1 Speckled deSSe ILD, DU in early disease (with or without nucleolar) Anti-RNA Speckled deSSe Rapid progression of skin thickening, SRC, polymerase III (with or without nucleolar) GAVE, Malignancy at diagnosis Anti-U3 RNP Nucleolar deSSe/1eSSc ILD, PAH, SRC, Lower Gl involvement in early disease, Myopathy Anti-Th/To Nucleolar LeSSc ILD, PAH Anti-Ul /Ul2 RNP Speckled deSSe/1eSSc ILD Anti-PM-Scl Nucleolar LeSSc Myositis, DM rash (myositis overlap) Anti-Ku Speckled LeSSc Myositis (myositis overlap) Anti-RuvBL1/2 Speckled deSSe Myositis (myositis overlap) Anti-Ul RNP Speckled LeSSc Inflammatory arthritis, Myositis, PAH (MCTD”) DM: dermatomyositis, DU: digital ulcer, GAVE: gastric antral vascular ectasia, Gl: gastrointestinal tract, ILD: interstitial lung disease, MCTD: mixed connective tissue disease, PAH: pulmonary arterial hypertension, SRC: scleroderma renal crisis T antibody and anticentromere antibody (ACA). Another group of antibodies, including anti-Ul RNP, anti-Ku, anti-PM-Scl antibodies, were first identified using double immunodiffusion technique. The remaining ANA speci- ficities were discovered using RNA or protein immuno- precipitation (IP) assay. SSc-specific ANAS target various nuclear components involved in essential cellular proc- esses, such as cell division, splicing, and transcription. These autoantibodies are rarely seen in patients with other connective tissue diseases without SSc features and thus are important diagnostic markers. In addition, de- tection of SSc-specific ANAs is clinically useful in classi- fying SSc patients into subtypes that are almost exclu- sively associated with characteristic clinical phenotypes (Table 1). SSe-specific ANAS are usually present at diag- nosis of SSc or even precede appearance of SSc-related clinical manifestations such as Raynaud's phenomenon. In addition, these autoantibodies do not switch from one antibody to another, and typically remain detectable throughout the disease course, regardless of the treat ment regimen. Patients rarely have two or more SSc- specific ANA together, indicating mutual exclusiveness. On the other hand, SSc-associated ANAs include anti- nucleolar organizing region 90 (NOR-90) and anti-B23 antibodies. Anti-NOR-90, also termed the human up- stream binding factor of RNAP L, was first reported in patients with cancer, but later in patients with connective tissue diseases, including SSc, Sjógren's syndrome, and ] Nippon Med Sch 2017; 84 (2) rheumatoid arthritis”. B23 is a nucleolar phosphoprotein overexpressed in many cancer cells, and is also targeted by cancer sera. Anti-B23 antibody is detected in <11% of SSc patients, and is associated with pulmonary arterial hypertension (PAH), often coexisting with anti-U3 RNP or anti-U1 RNP antibodies'. Anti-SSA/Ro and anti-SSB/ La can occur in SSc patients, but are usually associated with concomitant Sjógren's syndrome. Recently, it has been shown that tripartite motif family of protein 21 (TRIM21) or Ro52, which is one of components of the SSA/Ro autoantigen, is targeted by sera from patients with various connective tissue diseases in the absence of antiSSA/Ro antibody. A recent multicenter cohort study involving 963 patients with SSc has found that anti-TRIM21 antibodies are present in 20% of the patients and are associated with interstitial lung disease (ILD) and overlapping features with other connective tissue diseases" There are a small proportion of SSc patients who are negative for ANA by IIF. In a recent cohort study involv- ing 3,249 patients with SSc from a multicenter registry in North America, only 6.4% were negative for ANA!. ANA-negative SSc patients constitute a distinct subset with a greater proportion of males, less frequent and less severe vasculopathy, and more frequent lower gastroin- testinal (Gl) involvement. 57 M. Kuwana Anti-PM-Scl antibody produces a homogenous nucleolar pattern, and is rarely found in non-Caucasian patients”. Anti-PM-Scl-positive patients often present with the sub- acute myositis, but also have typical Raynaud's phe- nomenon and scleroderma skin changes, usually 1cSSc”. They are most frequently diagnosed as having SSc- polymyositis (PM) overlap, but a significant proportion of the patients have rashes consistent with dermato- myositis (DM). This antibody is found in more than 25% of SSc patients with myositis overlap, but in only 2% of SSc patients overall. Serious internal organ involvement is rare, leading to a favorable prognosis. Myositis is usu- ally mild and shows a good response to corticosteroids. In a recent large cross-sectional study of patients with idiopathic inflammatory myopathies, 9% had anti-PM- Sel antibody in the absence of any scleroderma skin changes”. 8. Anti-Ku Antibody Anti-Ku antibody was first identified by double immu- nodiffusion assay. The Ku autoantigen is now recognized as a heterodimer of 70-kD and 80-kD subunits. The prevalence of anti-Ku antibody in SSc patients is -2%”. Anti-Ku antibody is primarily detected in patients with SSc in overlap. The majority of patients have typical Ray- naud's phenomenon and scleroderma skin changes, usu- ally IcSSc. Concomitant inflammatory myopathy is com- mon, but some have additional features of lupus. Anti- Ku antibody is occasionally detected in patients with sys- temic lupus erythematosus (SLE) without SSc features, but additional lupus-associated autoantibodies such as anti-DNA antibodies are always positive. Disease onset in anti-Ku-positive patients is usually younger than 40 years. Internal organ involvement is infrequent and usu- ally mild if present, but arthritis is common. Anti-Ku an- tibody is associated with fewer vascular manifestations, such as DU or telangiectasia””, . Myositis is usually mild and shows a good response to corticosteroids, leading to favorable prognosis. 9. Anti-RuvBL1/2 Antibody This newly identified antibody recognizes a double hexamer consisting of RuvBL1 and RuvBL2, which is lo- cated in the nucleoplasm, by protein-IP assay”. Anti- RuvBL1/2 antibody is a rare antibody specificity de- tected in 12% of patients with SSc. This antibody pro- duces speckled nuclear staining with a high antibody titer on TIE. Patients with this antibody are mostly males and have a unique combination of clinical features, in- cluding deSSc and myositis overlap. Internal organ in- volvement is mild in general, but some develop signifi- 60 cant myocardial involvement. 10. Anti-U1 RNP Antibody Anti-Ul RNP antibody was first identified by double immunodiffusion assay, in association with anti-Sm anti- body, a lupus-specific ANA. Anti-Ul RNP antibodies are directed against the 70 K, A and C proteins associated with Ul RNA, while anti-Sm antibodies are directed against the B/B' and D proteins that are core compo- nents of the U series small nuclear RNAs involved in pre-messenger RNA splicing (Ul, U2, U4/U6, U5, and others)". Anti-Ul RNP antibody, which produces a pure speckled pattern with a high antibody titer, is primarily detected in patients with SSc in overlap. This antibody is preferentially found in African Americans and Orientals. Anti-Ul RNP antibody was first described as a serologic marker for mixed connective tissue disease (MCTD)”, but is also found in sera from patients with SSc, SLE, PM/ DM, or primary Sjógren's syndrome. Disease onset is at a relatively young age with mid 30's. SSc patients with this antibody usually present with inflammatory symptoms, such as myositis and arthritis. Raynaud's phenomenon and puffy fingers occur early in the disease, but later these patients develop typical manifestations of Sc. Most of them have IcSSc, although approximately 20% develop deSSc. Serious complications are relatively uncommon, but pulmonary complications, including PAH and ILD, are sometimes life-threatening. Prognosis is favorable in general, but PAH is the most common cause of death. Screening and Detection of SSc-specific ANAs in Routine Clinical Practice A conventional method for ANA detection is TIF on cul- tured HEp-2 cell slides. This technique is recommended as the autoantibody screening test because it is highly sensitive and provides additional information on the an- tibody titer and staining pattern. Speckled staining is often detected in patients with deSSc and suggests the presence of anti-topo 1 in case of a high ANA titer (21 : 320) or anti-RNAP III in case of a low ANA titer (<1 : 160). Anti-Ul RNP and anti-RuvBL1/2 antibodies, which are associated with SSc in overlap, also produce a high- titer speckled pattern. A nucleolar pattern is fairly spe- cific to SSc, and three major SSc-related anti-nucleolar an- tibodies are anti-U3 RNP, anti-Th/To, and anti-PM-Scl antibodies. Anti-RNAP III antibody also produces a nu- cleolar pattern when anti-RNAP 1 antibody coexists, but a concomitant speckled staining is always present. A dis- crete speckled pattern is often detected in patients with 1cSSc and suggests the presence of ACA. ] Nippon Med Sch 2017; 84 (2) Anti-Nuclear Antibodies in Scleroderma Identification of individual SSc-specific ANAS requires additional techniques, such as double immunodiffusion assay and/or IP assay, but convenient immunoassays such as enzyme immunoassays (EIA) are widely used in routine clinical practice, because of simplicity, reproduci- bility, speed, and ability to handle many samples at the same time. The majority of commercially available immu- noassays utilize recombinant autoantigens, which are ex- pressed in the bacterial or eukaryotic system, while some assays still use native proteins purified from cellular ex- tracts. It is necessary to use validated kits, since false- positive and false-negative results can occur. If the results obtained from ElA were inconsistent with clinical presen- tation, re-evaluation using original detection methods, such as IP assay, is highly recommended. Clinical Utility of SSc-specific ANAs 1. SSc Diagnosis SSc-specific ANAs are useful in diagnosis of SSc be- cause of their highly specific nature. In fact, the presence of ACA, anti-topo 1 antibody, or anti-RNAP III antibody is included in one of the classification criteria for SSc, which has been proposed by the American College of Rheumatology (ACR) and the European League against Rheumatism (EULAR)”. In addition, the presence of SSc- specific ANA and nailfold capillary abnormalities are identified as independent predictors for future develop- ment of Sc in patients with Raynaud's phenomenon, but without any features suggestive of connective tissue dis- eases", indicating that SSc-specific ANA are also useful in identifying patients with pre-SSc efficiently. 2. Disease Subsetting Classification of patients into deSSc and IeSSc subsets is useful in predicting future organ involvement and prognosis, but more precise subgrouping is feasible by considering SSc-specific ANAs because of their strong correlation with main organ manifestations (Table 1). For example, three major deSSc-specific ANAS, including anti-topo Í, anti-RNAP IIL, and anti-U3 RNP antibodies, cover >80% of deSSc patients, but major organ involve- ments linking to poor prognosis are apparently different. The presence of anti-topo 1 antibody in deSSc patients provides independent prognostic information with regard to a risk for progression of ILD and a greater risk of mortality”. In contrast, anti-RNAP III antibody has also been associated with increased mortality, primarily due to an increased prevalence of SRC”, but with improve- ment in the management of SRC, such associations may not be replicated in the future. On the other hand, PAH ] Nippon Med Sch 2017; 84 (2) still remains intractable condition with poor long-term survival even after introduction of a series of pulmonary vasodilators, and can occur in deSSc patients with anti- U3 RNP antibody. In addition, it is often difficult to classify patients into deSSc or leSSc early in the course of the disease when skin thickness is restricted to the distal portion of ex- tremities. In this case, information on SSc-specific ANAS is useful in predicting the future extent of skin involve- ment. If one of deSSc-associated ANA, including anti- topo L, antiRNAP II, and anti-U3 RNP antibodies, is present in circulation, disease modifying treatment should be indicated for preventing future organ damage at an early stage of deSSc. Conclusions In summary, circulating ANA. specificities are the best biomarkers for diagnosis and clinical subgrouping of SSc patients. 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