Molecular diagnosis of autoimmune skin diseases
Transcription
Molecular diagnosis of autoimmune skin diseases
Rom J Morphol Embryol 2014, 55(3 Suppl):1019–1033 RJME REVIEW Romanian Journal of Morphology & Embryology http://www.rjme.ro/ Molecular diagnosis of autoimmune skin diseases ROXANA CHIOREAN1), MICHAEL MAHLER2), CASSIAN SITARU1,3) 1) Department of Dermatology, University of Freiburg, Germany 2) INOVA Diagnostics, Inc., San Diego, CA, USA 3) BIOSS Centre for Biological Signalling Studies, Albert-Ludwigs University, Freiburg, Germany Abstract A wide range of skin diseases are associated with autoimmune responses against skin-specific or ubiquitous antigens. In many of these diseases, including autoimmune blistering disorders, collagenoses and vasculitides, extensive clinical and experimental evidence shows that autoreactive T-cells and/or autoantibodies play a major pathogenic role, allowing their classification as autoimmune diseases. The presence of tissue-bound and circulating autoantibodies does not only bear relevance for disease pathogenesis, but also allows developing robust diagnostic tools and molecular therapeutic approaches. Thus, various immunofluorescence methods, as well as molecular immunoassays, including enzyme-linked immunosorbent assay and immunoblotting, belong to the modern diagnostic algorithms for these disorders. This review article describes the immunopathological features of autoimmune skin diseases and the molecular assays currently available for their diagnosis and monitoring. Keywords: autoimmunity, molecular diagnosis, blistering skin diseases, collagen diseases. Introduction During the last decades, extensive research has focused on the pathogenesis and diagnosis of autoimmune skin diseases, which show a steadily increasing incidence and prevalence [1]. Criteria to classify a condition as an autoimmune disease were initially modeled on the Koch’s postulates by Ernest Witebsky in the 1950s and further refined by Rose and Bona in 1993 [2, 3]. They include circumstantial evidence from clinical and laboratory findings (e.g., the presence of antibody deposition in the affected tissue), indirect evidence, based on the reproduction of the disease by immunizing animals with the putative autoantigen and a direct proof, provided by disease induction through the passive transfer of autoantibodies and/or autoreactive T-cells [3]. The presence of tissue-bound and circulating autoantibodies does not only bear relevance for pathogenesis, but also allows developing robust diagnostic tools and molecular therapeutic approaches. Various molecular assays show increasing importance for the diagnosis and monitoring of a series of autoimmune skin diseases [4]. While in some diseases, including autoimmune blistering disorders, collagenoses and vasculitides, the detection of autoantibodies is highly important for diagnosis, in others, such as psoriasis, vitiligo or alopecia areata, the diagnosis is primarily made on clinical grounds [5–10]. In this article, we present an overview on the use of molecular immunoassays for the diagnosis and monitoring of autoimmune skin diseases. Overview of diagnostic procedures in autoimmune skin diseases As with other diseases, a thorough patient history and a skillful clinical investigation provide a strong index of suspicion for an autoimmune skin disease and guide the ISSN (print) 1220–0522 further diagnostic work-up. While the histopathological examination of a lesional skin biopsy is an important diagnostic tool, further imaging and laboratory investigations may be needed to support the diagnosis. Direct immunofluorescence (IF) microscopy Importantly, classifying a disease as autoimmune requires detection of tissue-bound and/or circulating autoantibodies. Deposits of immunoreactants (typically immunoglobulins and complement components) in the perilesional skin are detected by direct immunofluorescence (IF) microscopy, which remains the gold standard for the diagnosis of autoimmune bullous diseases and is an important part of the diagnostic work-up in cutaneous lupus and vasculitides [5, 11]. Thus, by direct IF microscopy deposition of different immunoreactants in the skin of the patients is detected using fluorochrome-labeled antibodies (e.g., specific for human IgG, IgA, IgM and C3) (Figure 1). For the direct IF, the site of the biopsy relative to the primary lesion (i.e., lesional or perilesional) should be selected depending on the suspected disease (Table 1). Table 1 – Optimal site of biopsy for direct immunofluorescence microscopy Suspected diagnosis Site of biopsy Autoimmune bullous Perilesional erythematous skin of fresh bullae. skin diseases Lesional skin. Lichen planus Active skin lesions, older than 60 days Collagenoses (exposed/not exposed to sun). Recent lesions, <24 h. Vasculitides While a strict perilesional biopsy is required when autoimmune skin blistering diseases are suspected, in order to avoid false negative results, for other diseases, including vasculitides and connective tissue disease, the biopsy should be performed from the lesion [11]. ISSN (on-line) 2066–8279 1020 Roxana Chiorean et al. Figure 1 – Detection of tissue-bound and serum autoantibodies in autoimmune skin diseases. Direct immunofluorescence (IF) and histopathological examination can be performed on a skin biopsy sample. IIF, ELISA, immunoblotting and immunoprecipitation can be performed using a serum sample. Direct IF microscopy detects presence of antigen deposits in a skin biopsy, using a fluorochrome-labeled antibody that binds to immunoreactant structures from patient’s skin. Indirect immunofluorescence (IIF) microscopy demonstrates presence of circulating autoantibodies. Autoantibodies from patient’s serum bind to the antigenic structures of the substrate (monkey esophagus, rat bladder). A second incubation, with a fluorochrome-labeled antibody, specific for the first antibody takes place after. ELISA method quantifies the serum level of specific autoantibodies. Plate wells are coated with an antigen and incubated with patient’s serum. Binding of specific autoantibodies to the antigenic protein takes place. Subsequently, wells are incubated with a second antibody, conjugated with an enzyme. A reaction takes place, leading to a change of color, which is directly proportional with the concentration of autoantibodies from patient’s serum. Indirect IF microscopy By indirect IF microscopy, autoantibodies in patient’s sera may be detected. As shown in the Figure 1, this method involves two incubation steps. First, autoantibodies from patient’s sera are incubated with a substrate containing the putative autoantigen(s). The choice of the substrate mainly depends on the disease suspected and on the antigen expression levels in different tissues (e.g., HEp2 cells, rat liver, granulocytes, monkey esophagus, or salt-split skin). Subsequently, in a second incubation step, the sections are incubated with a fluorochromelabeled antibody specific for human immunoglobulins classes [11]. To characterize the molecular specificity of circulating autoantibodies several immunoassays, including ELISA, immunoblotting and immunoprecipiation may be used. The enzyme-linked immunosorbent assay (ELISA) is used to quantify the level of antigen-specific autoantibodies in autoimmune skin diseases. For this purpose, microtiter plate wells are coated with the antigen and incubated with patient’s serum. Binding of specific autoantibodies to the antigenic protein is detected by a subsequent incubation with a secondary antibody specific for human immunoglobulins (e.g., IgG, IgM, IgA or IgE) conjugated with an enzyme. Finally, a chromogenic substrate is added and the ensuing color reaction is measured by spectrophotometry (Figure 1). Immunoblotting Immunoblotting (also referred to as Western blotting) may be also used to identify the molecular target of autoantibodies in autoimmune skin diseases. After separation by SDS-PAGE, the substrate (i.e., recombinant proteins or tissue extracts) are transferred to a nitrocellulose membrane and then incubated with patients’ sera. Subsequently, the membrane is incubated with an enzyme-conjugated secondary antibody and the protein bands are visualized by a color or chemiluminescent reaction [11]. Immunoprecipitation Immunoprecipitation is a technique used to precipitate the autoantigen(s) in solution. An extract of radioactively or biotin-labeled keratinocyte whole cell extracts or supernatant is mixed with patient’s serum or purified IgG. The formed immune complexes containing the autoantigen are precipitated using beads coated with protein A/G. The precipitates are separated by SDSPAGE, visualized by protein staining and/or may be subjected to immunoblotting, using antibodies specific for the putative autoantigen [5, 11]. Autoimmune skin blistering diseases Detection of autoantibodies, as well as characterization of their microscopic binding pattern and of their molecular specificity are obligate requirements for diagnosing an autoimmune blistering disease. The main autoantigens involved in the pathogenesis of autoimmune blistering diseases are depicted in Figure 2. A diagnostic algorithm for autoimmune blistering skin diseases is shown in Figure 3 and detailed below. Molecular diagnosis of autoimmune skin diseases 1021 Figure 2 – Localization of autoantigen in autoimmune dermatoses. In pemphigus diseases, autoantigens are represented by cell junction molecules of keratinocytes. In pemphigoid diseases, the autoantigens mainly belong to hemidesmosomal anchoring complex at the dermo-epidermal junction. In epidermolysis bullosa acquisita, the main autoantigen is collagen VII. Adapted from [4]. Pemphigus diseases Pemphigus vulgaris Pemphigus vulgaris is an autoimmune blistering disease, characterized by intraepidermal acatholytic cleavage and presence of autoantibodies against cell junction molecules of keratinocytes [12]. While several autoantigens have been incriminated as targets of autoantibodies in pemphigus, desmoglein 3 and desmoglein 1 were extensively characterized as autoantigens and are widely used in the routine diagnosis [13–17]. Direct IF microscopy demonstrates presence of intraepidermal deposits of IgG and/or C3, in a “cobblestone” or “fishnet” intercellular pattern [18]. Indirect IF microscopy is usually performed on monkey esophagus and shows binding of autoreactive IgG from patient’s sera to epithelia with an intercellular pattern [11, 18]. ELISA typically demonstrates the presence of autoreactive IgG against desmoglein 3. In addition, autoantibodies against desmoglein 1 may be also detected [5]. Pemphigus foliaceus Pemphigus foliaceus represents a superficial variant of pemphigus, characterized by skin blistering with lack of mucosal involvement, the presence of subcorneal cleavage and of autoantibodies against desmoglein 1 [5]. The main antigen is represented by desmoglein 1 [14]. Direct and indirect IF findings are similar to those in pemphigus vulgaris. Commercially available ELISA kits may be used to detect the presence of autoreactive IgG against desmoglein 1 [17, 19]. Key laboratory diagnostic features for pemphigus vulgaris and foliaceus are shown in Table 2. Table 2 – Key laboratory diagnostic features in pemphigus Investigation Direct IF microscopy Finding Intraepidermal deposits of IgG and/or C3, in a “cobblestone” or “fishnet” intercellular binding pattern. Indirect IF microscopy Intercellular binding pattern of (e.g., monkey autoantibodies (IgG) to epithelial cells. esophagus) Autoantibodies (IgG) against Immunoassay (ELISA) desmoglein 3 and desmoglein 1. Importantly, the profile of autoantibody molecular specificity correlates well with the clinical form of pemphigus [20]. In about 80% of pemphigus patients, detection of autoantibodies against desmoglein 3 alone correlates with a mucosal form of pemphigus vulgaris. Detection of autoantibodies to both desmoglein 3 and 1 is generally seen in patients with the mucocutaneous form of pemphigus vulgaris, while the exclusive reactivity to desmoglein 1 is documented in patients with pemphigus foliaceus [20, 21]. Figure 3 – Algorithm of diagnosis for autoimmune blistering skin diseases. 1022 Roxana Chiorean et al. Molecular diagnosis of autoimmune skin diseases Paraneoplastic pemphigus Paraneoplastic pemphigus is an autoimmune multiorgan syndrome characterized by a pathogenic autoimmune response to several epithelial proteins occurring in the setting of neoplasia [22, 23]. The autoantigens of paraneoplastic pemphigus include desmoglein 1 and 3, the bullous pemphigoid antigen of 230 kDa (BP230), periplakin, evoplakin, desmoplakin and the alpha-2macroglobulin-like-1 [22, 24]. Direct IF microscopy shows an association between IgG and/or C3 deposits in the epidermis, with an intercellular pattern and also along the dermal–epidermal junction, with a linear pattern. Indirect IF microscopy demonstrates binding of autoreactive IgG from patient’s sera to epithelial cells on monkey esophagus, in an intercellular pattern and might also show linear deposits in the basement membrane zone. A more specific analysis may be performed on transitional epithelia (e.g., rat bladder), a substrate rich in plakins, which facilitates detection of binding autoreactive IgG [5, 25]. The methods used for the characterization of the molecular specificity of autoantibodies in paraneoplastic pemphigus include immunoprecipitation using radioactively-labeled keratinocytes, ELISA and immunoblotting [5]. By ELISA or immunoblotting, specific autoantibodies may be detected using recombinant antigens (desmoglein 1 and 3, BP230, periplakin, evoplakin) or epidermal extracts (Table 3). Table 3 – Key laboratory diagnostic features in paraneoplastic pemphigus Investigation Finding IgG and/or C3 deposits in the epidermis Direct IF with an intercellular binding pattern and microscopy linear at the dermal–epidermal junction. Binding of autoantibodies (IgG) in an Indirect IF microscopy (e.g., intercellular pattern and linear deposits monkey esophagus) along the basement membrane. Immunoassay Evoplakin, periplakin, plectin, desmoglein (ELISA, immuno1 and 3, desmocollin 1 and 3, BP230, blotting, immunoalpha-2-macroglobulin-like-1. precipitation) Immunoprecipitation was the gold diagnostic standard, but, due to the costs and required time, it remained reserved to a couple of specialized laboratories worldwide [5, 26]. IgA pemphigus IgA pemphigus is a pemphigus variant characterized by the presence of autoreactive IgA against antigens on the surface of keratinocytes [27]. Two types of disease are distinguished, including the intraepidermal neutrophilic IgA dermatosis and the subcorneal pustular dermatosis. In the subcorneal pustular dermatosis subtype, the main autoantigen is represented by desmocollins 1–3 [5, 27]. While autoantibodies against desmoglein 1 and 3 may be found in a few patients with intraepidermal neutrophilic IgA dermatosis, the major autoantigen of this pemphigus variant is still elusive [28–30]. Direct IF microscopy demonstrates the presence of IgA deposits in the epidermis, with an intercellular pattern. By indirect IF microscopy on monkey esophagus, binding of autoreactive IgA from patient’s sera to epithelial cells with an intercellular pattern may be documented. To characterize the molecular 1023 specificity of autoreactive IgA, an indirect IF microscopy assay using desmocollin-transfected COS-7 cells was developed [5, 27]. Pemphigoid diseases Bullous pemphigoid. Pemphigoid gestationis Bullous pemphigoid is a blistering disease mostly affecting elderly, characterized by subepidermal cleavage and presence of autoantibodies against hemidesmosomal antigens [5, 11]. Pemphigoid gestationis is a subepidermal blistering disease associated with pregnancy or gestational trophoblastic diseases and presence of autoantibodies against hemidesmosomal proteins [31–33]. The major targets of autoantibodies in patients with bullous pemphigoid and pemphigoid gestationis are the hemidesmosomal components collagen XVII/BP180 and BP230 [34, 35]. Direct IF microscopy demonstrates presence of linear deposits of IgG and C3 at the dermo-epidermal junction [5, 11]. Indirect IF microscopy on salt-split skin demonstrates the presence of IgG and C3 antibodies that bind to the epidermal site of the artificial cleavage [36]. By ELISA or immunoblotting, autoantibodies against BP180 and BP230 may be detected. Key laboratory diagnostic features for bullous pemphigoid and pemphigus gestationis are shown in Table 4. Table 4 – Key laboratory diagnostic features of bullous pemphigoid and pemphigoid gestationis Investigation Direct IF microscopy Indirect IF microscopy (on salt-split skin) Immunoassay (e.g., ELISA or immunoblotting) Findings Linear IgG and/or C3 deposits along the dermal–epidermal junction. Binding of autoantibodies (IgG) to the epidermal side of the artificial cleavage. Autoantibodies (IgG) targeted against BP180 and/or BP230. Commercially available ELISA systems allow for easy quantitative detection of autoantibodies against the immunodominant region of BP180 and BP230 and are widely used as diagnostic and monitoring tools in pemphigoid diseases [37, 38]. Mucous membrane pemphigoid Mucous membrane pemphigoid is a subepithelial autoimmune blistering disease, primarily involving the mucosae [39, 40]. The main autoantigens are localized at the dermal–epidermal junction and include laminin 332 [41], α6β4 integrin [42] and BP180 [42, 43]. Direct IF microscopy reveals linear deposits of IgG, IgA and C3 antibodies at the dermal–epidermal junction. Patients with mucous membrane pemphigoid often show low serum autoantibody reactivity; binding of autoreactive IgG or IgA on the dermal or epidermal side may not be detected in up to 50% of the cases by indirect IF performed on human salt-split skin [5, 11]. Immunoblotting performed on extracellular matrix of keratinocytes and immunoprecipation of cultured keratinocytes are two highly sensitive methods used for anti-laminin 332 antibody detection [44]. Key laboratory diagnostic features for mucous membrane pemphigoid are shown in Table 5. Roxana Chiorean et al. 1024 Table 5 – Key laboratory diagnostic features in mucous membrane pemphigoid Investigation Direct IF microscopy Indirect IF microscopy (on salt-split skin) Immunoassay (e.g., ELISA or immunoblotting) Finding Linear deposits of IgG, A and/or C3 along the dermal–epidermal junction. Binding of autoantibodies (IgG/IgA) to the epidermal/dermal side of the artificial cleavage. Autoantibodies (IgG/A) against collagen XVII/BP180, laminin 332, α6β4 integrin. Linear IgA disease Table 6 – Key laboratory diagnostic features in linear IgA disease Direct IF microscopy Indirect IF microscopy (on salt-split skin) Immunoassay (e.g., ELISA or immunoblotting) Investigation Direct IF microscopy Indirect IF microscopy (on salt-split skin) Immunoassay (e.g., ELISA or immunoblotting) Finding Linear IgG and C3 deposits along the dermal–epidermal (DEJ) junction. Binding of autoantibodies to the dermal side of the artificial cleavage. Autoantibodies (IgG) targeted against laminin γ1. Epidermolysis bullosa acquisita Linear IgA disease is a subepidermal blistering disease showing linear IgA deposits along the epidermal basement membrane [45]. The main antigens are the 97 kDa protein (LABD97) and 120 kDa (LAD-1), which represent proteolytic cleavage products of BP180 protein [46, 47]. In some patients, the main antigen is represented by collagen VII. For this subtype of LAD, the name of IgA-mediated epidermolysis bullosa acquisita has been proposed [46]. Direct IF microscopy shows linear IgA deposits at the DEJ. Indirect IF microscopy on saltsplited skin demonstrates presence of autoreactive IgA binding to the epidermal or dermal side. Presence of specific autoreactive IgA is evidenced by ELISA and immunoblotting. Immunoblotting using recombinant BP180 ectodomain or supernatant of cultured keratinocytes demonstrates the presence of autoreactive IgA targeting the shed ectodomain of BP180 [47]. ELISA using recombinant BP180 or collagen VII can be performed, in order to measure the titer of autoreactive IgA [48]. Key laboratory diagnostic features for linear IgA disease are shown in Table 6. Investigation Table 7 – Key laboratory diagnostic features of antip200 pemphigoid Finding Linear IgA deposits along the dermal– epidermal junction. Autoantibodies (IgA) binding to the epidermal side of the artificial cleavage. Autoantibodies (IgA) specific the shed ectodomain of collagen XVII/BP-180 (LAD-1). Anti-p200 pemphigoid Anti-p200 pemphigoid is an autoimmune blistering disease, characterized by subepidermal blisters and autoantibodies targeting a 200 kDa protein (p200) [49]. The main antigen is represented by a dermal p200 protein, which has been recently identified as the laminin γ1 chain [50]. Direct IF microscopy demonstrates linear deposits of IgG and C3 at the dermal–epidermal junction. Indirect IF microscopy shows autoreactive IgG binding to the dermal side. Immunoblotting on dermal extracts demonstrates presence of specific antibodies against the 200 kDa protein [49, 51]. ELISA reveals presence of specific autoantibodies against laminin γ1 [52]. Key laboratory diagnostic features for anti-p200 pemphigoid are shown in Table 7. Epidermolysis bullosa acquisita is a chronic autoimmune blistering disease, characterized by subepidermal cleavage and presence of autoantibodies against collagen VII [5, 11, 53]. Key laboratory diagnostic features of epidermolysis bullosa acquisita are summarized in Table 8. Table 8 – Key laboratory diagnostic features in epidermolysis bullosa acquisita Investigation Direct IF microscopy Indirect IF microscopy (on salt-split skin) Immunoassay (e.g., ELISA or immunoblotting) Finding Linear IgG and/or C3 deposits along the DEJ. Binding of autoantibodies at the dermal side of the DEJ. Autoantibodies (IgG and/or IgA) targeted against collagen VII. Direct IF microscopy shows linear IgG and C3 at the dermal–epidermal junction. Indirect immunofluorescence on human salt-split skin demonstrates binding of autoreactive IgG or IgA to the dermal side. Immunoblotting using dermal recombinant proteins or dermal extract reveals presence of autoantibodies targeted against different epitopes of collagen VII. Levels of collagen VII-specific autoantibodies may be measured by ELISA, using various recombinant forms of the autoantigen [54–57]. Dermatitis herpetiformis Dermatitis herpetiformis is a chronic subepidermal autoimmune blistering disease, associated with a glutensensitive enteropathy and characterized by typical clinical and immunopathological findings [58, 59]. Direct IF microscopy demonstrates the presence of granular deposits along the dermal–epidermal junction, with an accentuation at the dermal papillae. Indirect IF microscopy on monkey esophagus reveals autoreactive IgA binding to endomysium. ELISA demonstrates presence of autoreactive IgA targeting the epidermal and tissue transglutaminase [60–62]. Key diagnostic features of dermatitis herpetiformis are shown in Table 9. Table 9 – Key laboratory diagnostic features in dermatitis herpetiformis Investigation Finding Direct IF microscopy Granular IgA deposits along the DEJ. Indirect IF microscopy IgA anti-endomysial autoantibodies. (e.g., monkey esophagus) Autoantibodies (IgA) against tissue/ Immunoassay epidermal transglutaminase. (e.g., ELISA) Connective tissue diseases Anti-nuclear antibodies (ANA) represent a serological Molecular diagnosis of autoimmune skin diseases hallmark for a group of systemic autoimmune diseases, including systemic lupus erythematosus (SLE), systemic sclerosis, idiopathic inflammatory myopathies (IIM), Sjögren’s syndrome and overlap syndromes [63, 64]. In addition, ANA may test positive in a series of additional autoimmune diseases, including autoimmune hepatitis, primary billiary cirrhosis and rheumatoid arthritis [65– 67]. However, ANA usually in low titers and generally showing specific binding patterns may be found also in 10–20% of the general population [68–70]. The majority of healthy individuals with positive ANA test have antibodies to dense fine speckled antigen. Using a specific assay for anti-DFS70 antibodies, it was demonstrated that these antibodies can be used to differentiate apparently healthy individuals from patients with connective tissue disease [71]. While, by definition, ANA comprise autoantibodies against components of the nucleus and mitotic apparatus, in practice, autoantibodies targeting further cellular components, including cytoplasmic organelles, cytoskeleton and cell membrane, which may be detected on the same substrate, are also reported [72]. Coining a more appropriate term for designating autoantibodies against ubiquitous cellular components with diagnostic relevance is a still unmet need in the field of autoimmune diagnostics. Although several methods for detection of ANA antibodies have been developed, indirect IF assay on HEp-2 cells (a cell line of laryngeal carcinoma cells) is considered the gold standard [73]. Table 10 summarizes the major autoantibody binding patterns on HEp-2 cells and their clinical correlations. 1025 In addition to their diagnostic significance, ANA may help to predict the course of the autoimmune disease. Thus, similar to other autoimmune diseases such as autoimmune diabetes mellitus, occurrence of ANA may precede with months or years the onset of clinical SLE. Furthermore, the appearance of autoantibodies in patients with SLE tends to follow a predictable course, with a progressive accumulation of specific autoantibodies before the onset of SLE, while patients are still asymptomatic [74]. Lupus erythematosus Lupus erythematosus encompasses a spectrum of clinical conditions, ranging from cutaneous disease to systemic manifestations [75]. Dermatologists distinguish several forms of cutaneous lupus, including erythematosus chronic cutaneous lupus erythematosus (CCLE), subacute lupus eythematosus (SCLE) and acute lupus erythematosus (ACLE; Figure 4) [76]. Table 10 – Immunofluorescent autoantibody binding patterns on HEp2 cells in systemic autoimmune diseases HEp-2 pattern Nuclear homogenous Autoantigen Clinical association dsDNA SLE SLE, drug-induced lupus Histones Nuclear rim (membranous) with metaphase staining dsDNA Nuclear matrix Heterogenous ribonuclear proteins (hnRNP) Coarse speckled Sm, U1,2,4,6-snRNP Fine speckled SSA/Ro, SSB/La, Mi-2, RNA-polymerase II SLE SLE Scleroderma Mixed connective tissue disease SLE Systemic sclerosis SLE Systemic sclerosis Dermatomyositis Nucleolar staining Pleomorphic speckled Centriole staining Midbody Centromere staining DFS70 Clumpy nucleolar SSc, SLE PCNA SLE Centriole/centrosome proteins Scleroderma Mitotic spindle agent (MSA2) Centromere proteins (CENP) DFS70/LEDGF CREST Scleroderma CREST syndrome Low likelihood of systemic autoimmune rheumatic disease Figure 4 – Main subtypes of lupus erythematosus. ACLE: Acute cutaneous lupus erythematosus; DLE: Discoid cutaneous lupus erythematosus; CCLE: Chronic cutaneous lupus erythematosus; SCLE: Subacute cutaneous lupus erythematosus; SLE: Systemic lupus erythematosus. Modified from Walling & Sontheimer, Am J Clin Dermatol, 2009 [76]. CCLE is defined by the presence of chronic, localized, circumscribed, hyperkeratotic and erythematous plaques, which often demonstrate healing with scars [77, 78]. Cutaneous discoid lupus erythematosus (CDLE) represents the most common subtype of CCLE [76]. The diagnosis of CCLE and CDLE is strongly suggested by the typical clinical appearance. Histopathological examination confirms the diagnosis and correlates well with the clinical picture [79]. While not strictly required for diagnosis, the direct IF microscopy may strengthen the suspected diagnosis, by documenting the presence of broad deposits of immunoglobulins and complement at the dermal– epidermal junction (the lupus band), more often found in the sun-exposed areas [18]. SCLE may be seen as an intermediate form of lupus in patients having extensive cutaneous involvement and some signs of systemic involvement, but without meeting enough criteria to be classified as SLE [76]. The main clinical features are photosensitivity and presence of skin lesions that heal without scarring [76, 80]. Histopathological examination confirms the diagnosis. Limited systemic involvement is often present. Up to 60–80% of 1026 Roxana Chiorean et al. the patients show positivity of ANA, more often specific for Ro/SS-A antigens. ACLE includes two forms: localized ACLE and generalized ACLE. While localized ACLE presents as a “butterfly malar rash”, generalized ACLE might present as a photosensitive maculopapular rash, often associated with systemic involvement [76]. Diagnosis of cutaneous lupus erythematosus is based on clinical, histo- and immunopathological findings [81]. The histology of the diseased skin of LE patients shows some typical characteristics, including vacuolar degeneration of the basal layer with thickened subepidermal basement membrane, as well as perivascular and periadnexal lymphocytic infiltrates, which may help to establish the diagnosis [76, 82]. The lupus band test is defined by the presence of linear deposits of IgG, A, M and/or C3 at the dermal–epidermal junction [18, 83]. Cytoid bodies and deposits in the keratinocyte nuclei may also be present [18]. Altogether, the lupus band may be documented in about 70–80% of patients with SLE, when sun-exposed non-lesional skin is tested and in about 55% cases, when sun-protected non-lesional skin is studied. In patients with CLE, the lupus band test of non-lesional skin is usually negative, although the lesional skin may frequently show immune deposits at the DEJ [84]. Systemic lupus erythematosus Systemic lupus erythematosus (SLE) represents a multiorgan disease associated with systemic autoimmunity [6]. The diagnosis is guided by criteria developed for clinical studies by the American College of Rheumatology (ACR) [85, 86], which propose that the presence of four out of the 11 listed criteria establish the SLE diagnosis (Table 11). Table 11 – ACR criteria for diagnosis of SLE 1. Malar rash. 2. Discoid rash. 3. Photosensitivity. 4. Oral ulcers (usually painless). 5. Nonerosive arthritis (involving two or more peripheral joints). 6. Pleuritis or pericarditis. 7. Renal disorder [(1) Persistent proteinuria >0.5 g/day or more than 3+ OR (2) Cellular casts – red cell, hemoglobin, tubular, granular, mixed]. 8. Neurological disorders (seizures or psychosis, in the absence of other offending causes). 9. Hematological disorder [(1) Hemolytic anemia with 3 reticulocytosis OR (2) Leukopenia <4000/mm on ≥2 3 occasions OR (3) Lymphopenia <1500/mm on ≥2 occasions) 3 OR (4) Thrombocytopenia <100.000/mm in the absence of offending drugs]. 10. Immunological disorder: Anti-DNA positive autoantibodies OR Anti-Sm positive autoantibodies OR Positive finding of antiphospholipid autoantibodies [(1) Abnormal serum level of IgM or IgG anticardiolipin antibodies OR (2) A positive test result for lupus anticoagulant OR (3) A false positive result for at least six months confirmed by immobilization of Treponema pallidum or FTA absorption test]. 11. An abnormal titer of ANA (antinuclear autoantibodies), at any time point, in the absence of drugs. Two of these criteria include the detection of autoantibodies, namely the presence of ANA and autoantibodies specific to certain antigens, which show a high association with SLE. The main types of autoantibodies detected in SCLE and SLE are shown in Table 12. Table 12 – Main targets of autoantibodies in lupus erythematosus Autoantibodies against Clinical association dsDNA Sm Ribosomal P SS-A/Ro-60 Ro-52/TRIM21 SS-B/La Nucleosomes SLE SCLE SLE SLE SLE SCLE SLE SLE SCLE SLE Positivity [percentage] 40–90% 40% 10–30% 10–30% 40–60% 60–90% 50–80% 20–30% 40% 60–90% High titers of ANA and/or the presence of autoantibodies specific to dsDNA, Sm, nucleosomes, PCNA are highly suggestive of SLE [64, 87–89]. Presence of an antiphospholipid syndrome should be ruled out by performing the lupus anticoagulant and testing for autoantibodies specific for cardiolipin and β2-glycoprotein I [90, 91]. Monoclonal gammopathies, which tend to occur more frequently in SLE patients [92], should be investigated by measuring serum concentrations of IgG, IgA and IgM, as well as by performing a serum electrophoresis and/or immunofixation in serum and urine. Scleroderma Scleroderma represents an autoimmune disease, with cutaneous and systemic involvement, characterized by the presence of an inflammatory reaction, followed by thickening and tightening of the dermis and damage of internal organs. Scleroderma may present as skinlocalized or systemic disease. Localized scleroderma Localized scleroderma (morphea) is a term encompassing a spectrum of sclerotic autoimmune diseases that primarily affect the skin, but also might involve underlying structures such as the fat, fascia, muscle, and bones [93, 94]. While the direct IF microscopy is usually negative, occasionally it may reveal the presence of granular IgM deposits along basement membrane zone [18]. Although ANA are sometimes positive, they are not specific for the localized scleroderma [93]. Systemic sclerosis Systemic sclerosis (SSc) is a clinically heterogeneous disease, characterized by dysfunction of fibroblasts (determining increased deposition of extracellular matrix), small vessel vasculopathy and production of autoantibodies [95]. Systemic sclerosis may present as a limited cutaneous systemic sclerosis (acrosclerosis-sclerodactyly) and diffuse cutaneous systemic sclerosis. CREST syndrome is considered a limited form. The ACR/EULAR criteria for classification of systemic sclerosis are shown in Table 13. Diagnostic criteria include the presence of specific autoantibodies. ANA are present in approximately 90% of patients with systemic sclerosis. While autoantibodies with several molecular specificities such as anti-centromere, anti-Scl-70 and anti-RNA Pol III antibodies are highly suggestive for systemic sclerosis, autoimmunity against a Molecular diagnosis of autoimmune skin diseases range of further antigens may associated with scleroderma and overlap syndromes (Table 14) [96–101]. Autoantibodies against PM-Scl75 Table 13 – The American College of Rheumatology/ European League Against Rheumatism criteria for the classification of systemic sclerosis Item/Sub-items Weight/ Score Skin thickening of the fingers of both hands extending proximal to the metacarpophalangeal joints (sufficient criterion) Skin thickening of the fingers (only count to the higher score) ▪ Puffy fingers ▪ Sclerodactyly of the fingers distal to the metacarpophalangeal joints, but proximal to the proximal interphalangeal joints Fingertip lesions (only count to the higher score) ▪ Digital tip ulcers ▪ Fingertip pitting scars Teleangiectasia Abnormal nailfold capillaries Pulmonary arterial hypertension and/or interstitial lung disease (maximum score is 2) ▪ Pulmonary arterial hypertension ▪ Interstitial lung disease Raynaud’s phenomenon Systemic sclerosis-related autoantibodies ▪ Anticentromere ▪ Anti-topoisomerase I ▪ Anti-RNA polymerase III 9 2 4 2 3 2 2 Clinical associations Specific antibodies Centromere (CENPA; CENPB) Scl-70 RNA-polymerase III Th/To-RNP Fibrillarin Associated antibodies U3-RNP B23 Ku U1-RNP Ro-52/TRIM-21 PDGFR NOR90 Clinical associations Dematomyositis/polymyositis Younger patients Active disease Joint contractures Increased myopathy Decreased GI involvement Arthritis Myositis Joint contractures Limited cutaneous systemic sclerosis Association with SLE Limited clinical utility Limited clinical utility Immunoblotting and ELISA kits for detection of autoantibodies associated with systemic sclerosis are commercially available and broadly used in clinical practice. Idiopathic inflammatory myopathies 2 2 3 3 Table 14 – Autoantibodies in systemic sclerosis Autoantibodies against PM-Scl100 1027 Limited cutaneous systemic sclerosis CREST syndrome Digital ischemia Risk of HTAP Esophageal involvement Diffuse systemic sclerosis Pulmonary fibrosis Cardiac involvement Neoplasms Diffuse systemic sclerosis Renal crisis Severe cutaneous involvement Limited cutaneous systemic sclerosis Pulmonary involvement Kidney involvement Gut involvement Severe prognosis Limited cutaneous systemic sclerosis Diffuse systemic sclerosis Cardiac involvement Skeletal muscle involvement Limited cutaneous systemic sclerosis Diffuse systemic sclerosis Pulmonary involvement HTAP Idiopathic inflammatory myopathies (IIM), including dermato- (DM) and polymyositis (PM) are chronic autoimmune diseases, which involve primarily the muscles and the skin, may be associated with neoplasia and may demonstrate systemic involvement [102, 103]. Diagnosis is guided by criteria published by Bohan and Peter (Table 15). Table 15 – Bohan and Peter criteria for diagnosis of dermatomyositis 1. Symmetric proximal muscle weakness. 2. Muscle biopsy. 3. Increased level of serum skeletal muscle enzymes. 4. Characteristic pattern on electromyography. 5. Typical cutaneous findings. Dermatomyositis may be associated with interstitial lung disease (ILD), in this case often labeled as antisynthetase syndrome (ASS), a condition characterized by myositis, interstitial lung disease, fever, arthritis, mechanic’s hands and Raynaud phenomenon [104]. Although direct IF microscopy occasionally reveals the presence of C5-9 deposits in small blood vessels or along the basement membrane zone, this feature is not characteristic for dermatomyositis [18]. Autoantibodies with different molecular specificities are involved in the pathogenesis of idiopathic inflammatory myopathies and associated disorders, several being specific for myositis, while others being also found in other systemic autoimmune diseases (Table 16). Table 16 – Autoantibodies in idiopathic inflammatory myopathies Myositis-specific antibodies Mi-2 SRP Jo-1, PL-7, PL-12, EJ, OJ, KS, YRS, Zo Clinical associations Characteristic skin involvement Photosensitivity Good prognosis Aggressive necrotizing myositis Low therapy response Antisynthetase syndrome Roxana Chiorean et al. 1028 Myositis-specific antibodies CADM-140/MDA-5 MJ/NXP-2 P155/140 (TIF1-γ) SAE HMGCR Myositis-associated antibodies Ro-52/TRIM-21 Ku PM/Scl Clinical associations Amyopathic dermatomyositis Rapidly progressive interstitial lung disease Juvenile dermatomyositis Calcinosis Good response at therapy Association with malignancy Severe skin disease Mild myopathy Necrotizing myopathy Statin-associated myopathy Clinical associations Association with Jo-1 positivity Interstitial lung disease Photosensitivity Joint involvement Overlap dermatomyositis/SLE Overlap systemic sclerosis/dermatomyositis Myositis-specific antibodies are highly selective, being found predominantly in patients with idiopathic inflammatory myopathies. They target nuclear and cytoplasmic components involved in gene transcription, protein synthesis and translocation [105–107]. Detection of autoantibodies to one or more of the eight aminoacyltransfer RNA synthetases – the most well recognized of which is anti-histidyl (Jo-1) – is necessary to establish the diagnosis of an antisynthetase syndrome [104]. Myositis-associated antibodies are found also in patients with overlap syndromes and other connective tissue diseases [107]. Other autoantibodies in idiopathic inflammatory myopathies are directed to the signal recognition particle (SRP), 3-hydroxy-3-methylglutaryl coenzyme (HMGCR), chromodomain helicase DNA binding protein 4 (Mi-2), SAE/small ubiquitin-related modifier (SUMO-1), MJ/nuclear matrix protein 2 (NXP2), melanoma differentiation-associated gene 5 (MDA5)/clinically amyopathic dermatomyositis p140 (CADM-140), transcription intermediary factor (TIF-1) gamma (p155/140) [106]. Immunoblotting/ELISA kits for detection of these autoantibodies are commercially available and are routinely used by physicians in clinical practice. Vasculitides Vasculitis is defined as an inflammation of blood vessels, characterized by destruction of the vessel wall [7]. According to the Chapel Hill Consensus, vasculitides have been classified in three main subtypes, depending on the vessel’s type involved, including large-, mediumand small-vessel vasculitis (SVV). Large-vessel vasculitides include Takayasu disease and giant cell temporal arteritis. Medium-sized vessel vasculitides encompass Kawasaki disease and polyarteritis nodosa. Small-vessel vasculitides include Churg–Strauss syndrome, (Wegener’s) granulomatosis with polyangitis, microscopic polyangiitis, cutaneous leukocytoclastic angiitis, essential cryoglobulinemic vasculitis and Henoch–Schönlein purpura [108]. A subgroup of small-vessel vasculitides are associated with autoreactive IgG against the cytoplasm of neutrophils (ANCA) [109]. Erythema elevatum et diutinum is increasingly regarded as a vasculitis variant associated with ANCA of the IgA class [110, 111]. Cutaneous vasculitis present with protean manifestations, including urticaria, infiltrative erythema, petechiae, purpura, purpuric papules, hemorrhagic vesicles and bullae, nodules, livedo racemosa, deep (punched out) ulcers and digital gangrene. Guided by clinical data, histopathological information coupled with direct IF microscopy and detection of ANCA greatly facilitate a precise and accurate diagnosis of localized and systemic vasculitis syndromes [7, 18, 109, 112]. A diagnostic algorithm in primary cutaneous vasculitides is shown in Figure 5 [113]. Figure 5 – Diagnostic algorithm in primary cutaneous vasculitides. Modified from Kawakami, J Dermatol, 2010 [113]. Molecular diagnosis of autoimmune skin diseases These varied morphologies are a direct reflection of size of the vessels and extent of the vascular bed affected, ranging from a vasculitis affecting few superficial, small vessels in petechial eruptions, to extensive pan-dermal small vessel vasculitis in hemorrhagic bullae, to muscular vessel vasculitis in lower extremity nodules with livedo racemosa [112]. Skin biopsy, extending to subcutis and taken from the earliest, most symptomatic, reddish or purpuric lesion is crucial for obtaining a high-yielding diagnostic sample. Based on histology, vasculitis can be classified on the size of vessels affected and the dominant immune cell mediating the inflammation (e.g., neutrophilic, granulomatous, lymphocytic, or eosinophilic) [112]. Disruption of small vessels by inflammatory cells, deposition of fibrin within the lumen and/or vessel wall coupled with nuclear debris allows for the confident recognition of small vessel, mostly neutrophilic vasculitis (also known as leukocytoclastic vasculitis). Direct IF microscopy typically reveals IgG, IgA and C3 deposits in the walls of dermal blood vessels [18, 112]. Measurement of ANCA is a rationale extension of the diagnostic work-up. While p-ANCA mainly target the myeloperoxidase and are often found in patients with Churg–Strauss syndrome or microscopic polyangiitis, c-ANCA often target the proteinase 3 (PR3) and are characteristic for granulomatosis with polyangiitis [109]. Cryoglobulins are immunoglobulins that precipitate in vitro, at temperatures less than 370C and produce organ damage by increased blood hyperviscosity and immunemediated mechanisms. Three types of cryoglobulinemia are recognized, according to the clonality and type of immunoglobulins. Type I consists of monoclonal immunoglobulin, generally either IgM or IgG. Type II cryoglobulins are a mixture of monoclonal IgM and polyclonal IgG. The IgM component of type II cryoglobulins has rheumatoid factor activity (i.e., these immunoglobulins bind to the Fc portion of IgG). Type III cryoglobulins are a mixture of polyclonal IgM and IgG [114]. Detection of cryoglobulins and/or cryofibrinogen is a mandatory diagnostic step when suspecting a cryoglobulinemic vasculitis [115, 116]. Cryoglobulinemia and cryofibrinogenemia may be primary (essential) or secondary to other underlying disorders, such as carcinoma, infection, vasculitis, collagen disease, or associated with cryoglobulinemia. Therefore, in this case, the presence of an underlying cause, such as hepatitis B, C, SLE, Sjögren’s syndrome or neoplasia should be ruled out. Laboratory diagnosis in further autoimmune skin diseases The autoimmune nature of further chronic skin diseases, including psoriasis, vitiligo, and alopecia areata is supported by extensive clinical and experimental evidence. Psoriasis is a T-cell-mediated inflammatory skin disorder, multifactorial in its etiology [8, 117]. It affects about 2% of the worldwide population. There is a wide range of clinical presentations of the disease, but the most common variety is the chronic plaque psoriasis. The evolution of a psoriatic lesion entails a complex interplay between environmental and genetic factors, which sets the scene for a cascade of events that activate 1029 dendritic cells and T-cells [8, 118]. Alopecia areata appears to be T-cell-dependent autoimmune disease with typical clinical manifestation [10, 119]. Vitiligo is a skin disease that causes patchy depigmentation of the epidermis and afflicts approximately 0.5% of the population, without preference for race or gender [120]. Its pathogenesis appears to involve both autoantibodies and T-cells, which may induce tissue damage by several mechanisms [121– 123]. The diagnosis of these dermatoses is primarily made on clinical grounds and the laboratory work-up plays an ancillary function. However, inflammation, liver and kidney parameters may be used to monitor the response to treatment and the side effects of the systemic antiinflammatory therapies. In further inflammatory dermatoses, including chronic ulcerative stomatitis, lichen planus and erythema multiforme, an autoimmune ethiopathogenesis is suspected, but not yet proven by clinical and experimental data. In lichen planus, in addition to histopathology, the direct IF microscopy is a useful diagnostic tool, which may show the presence of cytoid bodies and shaggy fibrinogen deposition at the dermal–epidermal junction [18, 124, 125]. Chronic ulcerative stomatitis manifests more frequently in Caucasian middle-aged women with painful, exacerbating and remitting oral erosions, and ulcerations. The histological features are non-specific, with a chronic inflammatory infiltrate, often appearing similar to oral lichen planus. Diagnosis of chronic ulcerative stomatitis requires surgical biopsy with immunofluorescence microscopic examination. Immunofluorescence studies show circulating and tissue-bound autoantibodies to a protein, DeltaNp63alpha, which is a normal component of stratified epithelia [126, 127]. Perspectives and conclusion The future development of state-of-the-art diagnostic tests for autoimmune diseases is directly linked to sustained and extensive fundamental and translational research. A detailed definition of pathogenic human autoantibodies would allow the development of quantitative tests, which would ideally reflect disease activity in patients [5, 11]. A further important avenue for improvement is related to the use of multiplex technologies, which allow multiple antibodies to be analyzed simultaneously, contributing to diagnosis and patient stratification in the field of autoimmune diseases. The need for standardization may be addressed by robotic preparation of slides and development of a computer-aided IF pattern analysis system [128, 129]. Advanced systems are currently being developed, that provide fully automated readings of IF images and software algorithms for the mathematical description of the IF patterns. These tests, using collections of up to hundreds of antigens are amenable to full automation and high-throughput screening for autoantibodies and should greatly reduce the costs involved [5]. Detection of tissue-bound and circulating autoantibodies plays an essential role in the diagnosis of autoimmune skin diseases. The target antigens of these autoantibodies have been extensively characterized over the past decades. Detection of tissue-bound and serum auto- 1030 Roxana Chiorean et al. antibodies and characterization of their molecular specificity allows for a rapid and accurate diagnosis of autoimmune skin diseases. Various IF methods, as well as molecular immunoassays, including ELISA and immunoblotting, became an essential part of the modern diagnostic algorithms for these disorders. Fundamental and translational research combining pathogenetic studies, bioinformatic analyses, automation and high throughput approaches will greatly facilitate the development of a next generation of improved diagnostic tools [5, 11]. Acknowledgments The work of the authors is supported by grants from the Deutsche Forschungsgemeinschaft SI-1281/5-1 (CS), from the European Community’s Seventh Framework Programme [FP7–2007–2013] under grant agreement No. HEALTH–F4–2011–282095 (CS). 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Corresponding author Cassian Sitaru, MD, PhD, Department of Dermatology, University of Freiburg, Hauptstrasse 7, D–79104 Freiburg, Germany; Phone +49–(0)761–27067690, Fax +49–(0)761–27068290, e-mail: cassian@mail.sitaru.eu, cassian. sitaru@uniklinik-freiburg.de Received: December 10, 2013 Accepted: November 5, 2014