Antibodies in Scleroderma: Direct Pathogenicity and Phenotypic Associations Lorinda Chung, MD* and Paul J
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Antibodies in Scleroderma: Direct Pathogenicity and Phenotypic Associations Lorinda Chung, MD* and Paul J. Utz, MD Address pathology manifests as Raynaud’s phenomenon and *Division of Immunology and Rheumatology, Department of Medicine, ischemic digital loss, while the excessive collagen deposi- Stanford University School of Medicine, 1000 Welch Road, tion results in skin thickening and fibrosis in various Suite 203, Stanford, CA 94305, USA. E-mail: [email protected] organs, such as the lungs, heart, kidneys, or gastrointesti- nal tract [3•]. B cells from patients with scleroderma Current Rheumatology Reports 2004, 6:156–163 Current Science Inc. ISSN 1523–3774 overexpress CD19, resulting in hyper-responsiveness and Copyright © 2004 by Current Science Inc. autoantibody formation [4]. Although the pathogenic role of certain autoantibodies associated with sclero- derma can be explained on a molecular level, it is unclear Scleroderma is an autoimmune disease involving endothelial whether other autoantibodies are primary drivers of cell damage and fibroblast overproduction of extracellular pathology or represent a secondary response. A subset of matrix. Several autoantibodies present in the sera of autoantibodies correlates with clinical expression of dis- patients with scleroderma, including anti-endothelial cell, ease and these may serve as prognostic markers. antifibroblast, anti–matrix metalloproteinase, and antifibril- Several clinical subtypes of scleroderma have been lin-1 antibodies, may directly contribute to disease patho- identified and are associated with distinct autoantibody genesis. Scleroderma also is characterized by the presence patterns. Diffuse scleroderma is clinically characterized of antinuclear and antinucleolar antibodies, which correlate by skin thickening involving the face, neck, trunk, and with particular phenotypes. These include antitopoiso- proximal upper and lower extremities, as well as signifi- merase-I, anticentromere, antihistone, anti-polymyositis/ cant internal organ involvement, including the lungs, scleroderma, anti-Th/To, anti-U3-small nucleolar heart, gastrointestinal tract, and kidney. Diffuse sclero- ribonucleoprotein particle, anti-U1-small nuclear ribonucle- derma is classically associated with antitopoisomerase-I oprotein particle, anti-RNA polymerase, and anti-B23 anti- antibodies (anti-topo-I or anti-Scl-70) and the absence of bodies. Other antibodies classically associated with other anticentromere antibodies (ACA) [5]. Limited sclero- autoimmune diseases, such as antiphospholipid, antineutro- derma involves skin thickening in the face, neck, and dis- phil cytoplasmic, and antimitochondrial antibodies, also tal extremities, with frequent development of isolated have been described in patients with scleroderma. This pulmonary hypertension and ischemic digital loss. A review will summarize the various autoantibodies associ- form of limited scleroderma with calcinosis, Raynaud’s ated with scleroderma, their putative pathogenic roles, and phenomenon, esophageal dysmotility, sclerodactyly, and their phenotypic correlations. telangiectasias (CREST) is characterized by the presence of ACA [5]. Overlap syndromes, such as mixed connec- tive tissue disease (MCTD), with features of systemic Introduction lupus erythematosus (SLE), polymyositis (PM), rheuma- Scleroderma is a systemic connective tissue disease char- toid arthritis (RA), and scleroderma are associated with acterized by vascular damage and fibrosis involving the anti-U1-small nuclear ribonucleoprotein particle (U1- skin and other internal organs. Disease course, severity, snRNP) antibodies [5]. This review summarizes the clas- and organ involvement are variable from patient to sical and novel autoantibodies associated with sclero- patient, and overlap syndromes with other autoimmune derma, their putative pathogenic functions, and their conditions can occur [1]. The pathogenesis of this dis- correlation with disease expression. ease is thought to involve three processes: 1) endothelial cell damage and intimal hyperplasia; 2) fibroblast activa- tion and overproduction of extracellular matrix compo- Antibodies Involved in Disease Pathogenesis nents; and 3) stimulation of the immune response, Several autoantibodies have been discovered in the sera leading to production of autoantibodies [2]. The vascular of patients with scleroderma that may be directly patho- Antibodies in Scleroderma: Direct Pathogenicity and Phenotypic Associations • Chung and Utz 157 Table 1. Autoantibodies with direct pathogenicity in scleroderma Autoantibody Role in pathogenesis Clinical associations Study Anti-endothelial cell Incite vascular injury by inducing endothelial Ischemic digital infarcts; Worda et al. [6] and cell apoptosis pulmonary arterial Negi et al. [7] hypertension Antifibroblast Induce fibroblast production of ICAM-1 and Limited scleroderma Chizzolini et al. [8] IL-6, leading to vascular damage and ECM production Anti–matrix Inhibit MMP-1 collagenase activity Diffuse scleroderma Sato et al. [9] metalloproteinase Antifibrillin-1 Induce instability of microfibrils resulting in Choctaw American Indian and Tan et al. [11] and ECM accumulation Japanese ethnic backgrounds Wallis et al. [12] ECM—extracellular matrix; ICAM-1—intercellular adhesion molecule-1; IL-6—interleukin-6; MMP-1—matrix metalloproteinase-1. genic (Table 1). These include anti-endothelial cell, anti- increased levels of anti-MMP-1 immunoglobulin (Ig) G in fibroblast, anti–matrix metalloproteinase (MMP), and sera from patients with scleroderma compared with antifibrillin antibodies. Currently, these autoantibodies healthy control subjects and patients with other auto- are not routinely analyzed in the clinical setting. Further immune diseases. The antibody titers correlated with the studies on large cohorts of scleroderma patients need to degree of fibrosis in the involved tissues, with higher titers be performed to define the sensitivity and specificity of in patients with diffuse compared with limited disease, these autoantibodies. presumptively by inhibiting MMP-1–mediated collagenase activity [9]. Anti-endothelial cell antibodies Anti-endothelial cell antibodies have been found in 28% Antifibrillin-1 antibodies to 71% of sera from patients with scleroderma [6] and are Elastic microfibrils of the extracellular matrix are partially clinically associated with ischemic digital infarcts and pul- composed of a glycoprotein component called fibrillin-1. monary arterial hypertension [7]. These antibodies may The tight skin mouse represents a genetic model for have a direct pathogenic role by inciting vascular injury. human scleroderma. These mice have a mutation within Worda et al. [6] recently demonstrated that transfer of anti- the fibrillin-1 gene that is thought to be responsible for endothelial cell antibody–positive sera into normal increased collagen deposition and thickening of the skin. chicken embryos induced endothelial cell apoptosis in The tight skin mice also generate autoantibodies to fibril- vivo. However, a sclerodermatous phenotype did not lin-1, implicating this protein as a possible target in disease develop in these animals, implying that factors other than pathogenesis [10]. Tan et al. [11] reported the presence of anti-endothelial cell antibodies are required for disease antifibrillin antibodies in approximately 80% of sera from expression [6]. scleroderma patients of Choctaw American Indian and Jap- anese ethnic backgrounds; however, less than 50% of Cau- Antifibroblast antibodies casian patients possessed antibodies to fibrillin-1 antigens. Autoantibodies directed against fibroblasts have been Wallis et al. [12] showed that microfibrils from fibroblasts recently observed in 58% of sera from 69 patients with dif- of patients with scleroderma are unstable, possibly because fuse and limited scleroderma. These antibodies were of antibodies against fibrillin-1, with resultant dysregula- reported to induce fibroblast activation in vitro, resulting tion of extracellular matrix accumulation. in increased expression of intercellular adhesion molecule- 1 and production of the proinflammatory cytokine inter- leukin-6 [8]. Intercellular adhesion molecule-1 mediates Antibodies Associated adhesion and transendothelial migration of mononuclear with Clinical Phenotypes cells, leading to vascular damage and inflammation, Antinuclear antibodies whereas interleukin-6 release is associated with increased Antinuclear antibodies (ANA) are present in the sera of extracellular matrix production [8]. more than 95% of scleroderma patients, with certain clin- ical phenotypes associated with specific ANAs [13•]. Anti–matrix metalloproteinase antibodies Anti-topo-I and ACA are classically associated with sclero- The degradation of extracellular matrix is dependent on a derma, and respectively demonstrate nucleolar/homo- family of endopeptidases referred to as the MMP. MMP-1 is geneous and centromeric staining patterns on ANA responsible for initiating the breakdown of collagen types screening by immunofluorescence [14]. Antihistone anti- I, II, and III, which are overexpressed in the skin of patients bodies (AHA), most commonly associated with drug- with scleroderma [9]. Sato et al. [9] demonstrated induced lupus, can occur in patients with scleroderma, 158 Scleroderma and demonstrate a homogenous staining pattern on Antinucleolar antibodies immunofluorescence [14]. These three autoantibodies Antinucleolar antibodies have been reported in 15% to are widely available in the