A highly sensitive and simple assay for the detection of circulating autoantibodies against full-length bullous pemphigoid antigen 180

The Diagnosis and Blistering Mechanisms of Mucous Membrane Pemphigoid

Mucous membrane pemphigoid (MMP) is a mucous membrane-dominated autoimmune subepithelial blistering disease that is caused by autoantibodies against various autoantigens in basement membrane zone (BMZ) proteins, including collagen XVII (COL17). Clinicians face diagnostic problems in detecting circulating antibodies and targeted antigens in MMP. The diagnostic difficulties are mainly attributed to the low titers of MMP autoantibodies in sera and to heterogeneous autoantigens. Additionally, no unanimous diagnostic criteria have been drawn for MMP, which can result in delayed diagnoses or misdiagnoses. This review aims to integrate and present currently available data to clarify diagnostic strategies and to present diagnostic criteria for MMP. The ultimate blistering mechanism in MMP has not been elucidated, and such mechanism is especially obscure in COL17-type MMP. In bullous pemphigoid (BP), which is the most common autoimmune subepidermal blistering disease, some patients show oral lesion as well as predominant skin lesions. However, there is no fundamental explanation for the onset of oral lesions in BP. This article summarizes innovative research perspectives on the pathogenesis of oral lesions in pemphigoid. Finally, we propose a potential pathogenesis for COL17-type MMP.

Diagnostic procedures for autoimmune vesiculobullous diseases: A review

Oral soft tissues are affected by numerous pathologic conditions of variable etiology and hence their appropriate management relies on their accurate diagnosis. Clinical identification of intact vesicle and bulla in the oral cavity is really a challenge due to the regular irritation and the friable nature of oral mucosa. Rupture of these lesions leads to erosions or ulcerations on the surface, hence making the diagnosis of vesiculobullous (VB) lesions is even more difficult due to the fact that the differential diagnosis along with VB lesions will also include ulcerative, immunological-mediated diseases, and neoplasms and systemic diseases. Hence, knowledge of the clinical presentation of these disorders and the relevant diagnostic procedures is important not just for dermatologists, but also for general practitioners and dentists. In this article, the various procedures have been explained that can be used for the diagnostic purpose of VB lesions.

Serological diagnosis of autoimmune bullous skin diseases: prospective comparison of the BIOCHIP mosaic-based indirect immunofluorescence technique with the conventional multi-step single test strategy

BACKGROUND

Various antigen-specific immunoassays are available for the serological diagnosis of autoimmune bullous diseases. However, a spectrum of different tissue-based and monovalent antigen-specific assays is required to establish the diagnosis. BIOCHIP mosaics consisting of different antigen substrates allow polyvalent immunofluorescence (IF) tests and provide antibody profiles in a single incubation.

METHODS

Slides for indirect IF were prepared, containing BIOCHIPS with the following test substrates in each reaction field: monkey esophagus, primate salt-split skin, antigen dots of tetrameric BP180-NC16A as well as desmoglein 1-, desmoglein 3-, and BP230gC-expressing human HEK293 cells. This BIOCHIP mosaic was probed using a large panel of sera from patients with pemphigus vulgaris (PV, n=65), pemphigus foliaceus (PF, n=50), bullous pemphigoid (BP, n=42), and non-inflammatory skin diseases (n=97) as well as from healthy blood donors (n=100). Furthermore, to evaluate the usability in routine diagnostics, 454 consecutive sera from patients with suspected immunobullous disorders were prospectively analyzed in parallel using a) the IF BIOCHIP mosaic and b) a panel of single antibody assays as commonly used by specialized centers.

RESULTS

Using the BIOCHIP mosaic, sensitivities of the desmoglein 1-, desmoglein 3-, and NC16A-specific substrates were 90%, 98.5% and 100%, respectively. BP230 was recognized by 54% of the BP sera. Specificities ranged from 98.2% to 100% for all substrates. In the prospective study, a high agreement was found between the results obtained by the BIOCHIP mosaic and the single test panel for the diagnosis of BP, PV, PF, and sera without serum autoantibodies (Cohen's κ between 0.88 and 0.97).

CONCLUSIONS

The BIOCHIP mosaic contains sensitive and specific substrates for the indirect IF diagnosis of BP, PF, and PV. Its diagnostic accuracy is comparable with the conventional multi-step approach. The highly standardized and practical BIOCHIP mosaic will facilitate the serological diagnosis of autoimmune blistering diseases.

Clinical features and practical diagnosis of bullous pemphigoid

Bullous pemphigoid (BP) represents the most common autoimmune subepidermal blistering disease. BP typically affects the elderly and is associated with significant morbidity. It has usually a chronic course with spontaneous exacerbations. The cutaneous manifestations of BP can be extremely protean. While diagnosis of BP in the bullous stage is straightforward, in the non-bullous stage or in atypical variants of BP signs and symptoms are frequently non-specific with eg, only itchy excoriated, eczematous, papular and/or urticarial lesions that may persist for several weeks or months. Diagnosis of BP critically relies on immunopathologic examinations including direct immunofluorescence microscopy and detection of serum autoantibodies by indirect immunofluorescence microscopy or BP180-ELISA.

The diagnosis and treatment of autoimmune blistering skin diseases

BACKGROUND

Autoimmune blistering skin diseases are a heterogeneous group of disorders associated with autoantibodies that are directed against desmosomal structural proteins (in pemphigus diseases) or hemidesmosomal ones (in pemphigoid diseases and epidermolysis bullosa acquisita), or else against epidermal/ tissue transglutaminases (in dermatitis herpetiformis). Knowledge of the clinical presentation of these disorders and of the relevant diagnostic procedures is important not just for dermatologists, but also for general practitioners, ophthalmologists, ENT specialists, dentists, gynecologists, and pediatricians.

METHODS

The literature on the subject was selectively reviewed. There are no existing guidelines available in Germany.

RESULTS

The recently developed sensitive and specific assays for circulating autoantibodies in these diseases now enable a serological diagnosis in about 90% of cases. The incidence of autoimmune blistering skin diseases in Germany has doubled in the last 10 years, to a current figure of about 25 new cases per million persons per year, because of improved diagnostic techniques as well as the aging of the population. Accurate and specific diagnosis is the prerequisite for reliable prognostication and appropriate treatment. For severe and intractable cases, more effective treatments have recently become available, including immunoadsorption, high-dose intravenous immunoglobulin, the anti-CD20 antibody rituximab, and combinations of the above.

CONCLUSION

The diagnostic assessment of autoimmune blistering skin diseases can be expected to improve in the near future as new serological testing systems are developed that employ recombinant forms of the target antigens. The treatments currently in use still need to be validated by prospective, controlled trials.

Enzyme-linked immunosorbent assay using multimers of the 16th non-collagenous domain of the BP180 antigen for sensitive and specific detection of pemphigoid autoantibodies

Bullous pemphigoid (BP) and pemphigoid gestationis (PG) are acquired autoimmune subepidermal blistering diseases characterized by autoantibodies against the hemidesmosomal proteins BP180/type XVII collagen and BP230. In the vast majority of BP and PG patients, these autoantibodies bind to epitopes clustered within the 16th non-collagenous domain of BP180. An ELISA system for the detection of these autoantibodies was developed and evaluated using 16th non-collagenous domain (NC16A) tetramers instead of monomers. In contrast to antigens fused to large proteins used in the past for the detection of autoantibodies against type XVII collagen, tetrameric antigen fragments bearing a small hexahistidine tag allow for high expression levels without the need to cleave off the fusion partner. Using tetrameric BP180 NC16A, positive reactions were found in 106 (89.8%) of 118 randomly selected BP sera and in all of 20 (100%) randomly selected PG sera, whereas only 2.2% of a large cohort of control subjects were positive in this assay, including patients with rheumatoid arthritis (two of 107), progressive systemic sclerosis (two of 50), systemic lupus erythematosus (one of 72), and healthy blood donors (10 of 494). Thus, the sensitivity and specificity of the new anti-tetrameric NC16A ELISA were 89.9% and 97.8% respectively. Levels of circulating autoantibodies against BP180 paralleled disease activity in the pemphigoid patients. In conclusion, the use of tetrameric NC16A in ELISA results in a sensitive and specific tool for diagnosis and monitoring of BP and PG.

Autoimmune subepidermal blistering diseases in Uganda: correlation of autoantibody class with age of patients

BACKGROUND

No data are available on the incidence and immunoreactivity of autoimmune subepidermal blistering skin diseases in East Africa.

METHODS

All patients with frank blisters/erosions on the skin and/or mucous membranes that attended the Department of Dermatology at Mbarara University, Uganda, from May 2000 to June 2002, were investigated. The diagnosis was based on the clinical presentation and on the presence of circulating autoantibodies detected by indirect immunofluorescence microscopy on 1 m NaCl-split human skin and by Western blotting of recombinant and cell-derived forms of BP180, BP230, and type VII collagen.

RESULTS

Twenty-two patients with autoimmune subepidermal blistering skin disorders were identified, including nine with bullous pemphigoid (41%), four with linear immunoglobulin A (IgA) disease (18%), three with mucous membrane pemphigoid (14%), two with linear IgG/IgA bullous dermatosis (9%), and one each with cicatricial pemphigoid and epidermolysis bullosa acquisita (5%). In addition, two patients with immunoreactivity to both the epidermal and dermal side of salt-split skin by indirect immunofluorescence microscopy, who were unreactive to type VII collagen, were provisionally diagnosed as "mixed pemphigoid" (9%). In patients with subepidermal blistering diseases, IgG reactivity correlated significantly with old age, whereas younger patients preferentially developed IgA autoantibodies (P = 0.024).

CONCLUSIONS

The age of patients with autoimmune subepidermal blistering diseases appears to influence the immunoglobulin class of autoantibodies. The high frequency of IgA autoantibodies in Ugandan patients may be explained by the age distribution of the Ugandan population.

Number III Mucous membrane pemphigoid

Mucous membrane pemphigoid (MMP) is a sub-epithelial vesiculobullous disorder. It is now quite evident that a number of sub-epithelial vesiculobullous disorders may produce similar clinical pictures, and also that a range of variants of MMP exist, with antibodies directed against various hemidesmosomal components or components of the epithelial basement membrane. The term immune-mediated sub-epithelial blistering diseases (IMSEBD) has therefore been used. Immunological differences may account for the significant differences in their clinical presentation and responses to therapy, but unfortunately data on this are few. The diagnosis and management of IMSEBD on clinical grounds alone is impossible and a full history, general, and oral examination, and biopsy with immunostaining are now invariably required, sometimes supplemented with other investigations. No single treatment regimen reliably controls all these disorders, and it is not known if the specific subsets of MMP will respond to different drugs. Currently, apart from improving oral hygiene, immunomodulatory-especially immunosuppressive-therapy is typically used to control oral lesions. The present paper reviews pemphigoid, describing the present understanding of this fascinating clinical phenotype, summarising the increasing number of subsets with sometimes-different natural histories and immunological features, and outlining current clinical practice.

Trehalose conserves expression of bullous pemphigoid antigen 180 during desiccation and freezing

Bullous pemphigoid antigen 180 (BP180) is targeted by autoantibodies in a variety of subepidermal blistering skin diseases. We have recently developed a simple, highly specific and sensitive immunofluorescence (IF) assay for the detection of circulating antibodies against BP180. This novel assay involves the expression of full-length (FL) BP180 in Sf21 insect cells that are then examined under IF microscopy after staining with anti-BP180 antibodies. Application of this assay as a routine diagnostic tool requires long-term storage of FL-BP180, which can result in substantial loss of expression. Here, we show that the disaccharide trehalose, a natural cryo- and lyoprotectant, is capable of preserving the FL-BP180 antigen expressed in Sf21 insect cells under various (dry) storage conditions including 40 degrees C, room temperature (RT), 4-8, -20, and -80 degrees C. The protective effect was dose-dependent reaching a maximum at about 200 mM trehalose. Trehalose was superior to other sugars or conventional cryoprotective agents (e.g. sucrose, myo-inositol, DMSO) in preventing greatly reduced antigen expression. Trehalose conserved the expression of both extra- and intracellular epitopes of FL-BP180. Interestingly, protection of the intracellular domain was only observed when trehalose was introduced into the cytosol. Trehalose significantly prolonged the storage time of FL-BP180 expressed in Sf21 insect cells, thus permitting the routine use of the IF assay in clinics for the detection of serum antibodies. The method described here has potential applications for the preservation of other transmembrane proteins.