Erythema multiforme associated human autoantibodies against desmoplakin I and II: biochemical characterization and passive transfer studies into newborn mice

Desmoplakin I/II immunohistochemical staining may be a helpful tool in differentiating cutaneous graft versus host disease from the erythema multiforme, Stevens-Johnson syndrome, and toxic epidermal necrolysis spectrum disorders

Cutaneous graft versus host disease (cGVHD) has substantial clinical and histopathologic overlap with erythema multiforme (EM), Stevens-Johnson syndrome (SJS), and toxic epidermal necrolysis (TEN). This overlap can make it difficult to distinguish these disorders in patients who have received hematopoietic transplants. We sought to evaluate the utility of Dp I/II immunohistochemical stain in differentiating EM/SJS/TEN and cGVHD in a large cohort. Skin biopsy specimens from patients with cGVHD (n = 58) and EM/SJS/TEN (n = 60) were evaluated for Dp I/II expression by immunohistochemistry. We found a statistically significant difference in Dp I/II staining between cGVHD (all grades) and EM/SJS/TEN (mean scores 1.62 and 2.14, respectively; p < 0.005), as well as between Grades 2 + 3 cGVHD and EM/SJS/TEN (mean scores 2.26 and 1.62, respectively; p < 0.005), while we did not find a significant difference between Grade 4 cGVHD and EM/SJS/TEN (mean scores 1.69 and 1.62, respectively; p = 0.71). Dp I/II immunostain may be useful for differentiating EM/SJS/TEN from Grade 2 and Grade 3 cGVHD, especially in clinically ambiguous cases without extracutaneous GVHD.

Indirect immunofluorescence on rat bladder epithelium in patients with pemphigus vulgaris with an extended follow-up

Background

Indirect immunofluorescence (IIF) on rat bladder epithelium (RBE) has been widely used to detect anti-plakin antibodies present in paraneoplastic pemphigus (PNP). However, anti-plakin antibodies have also been found in a group of patients with pemphigus vulgaris (PV).

Objectives

To assess the reactivity rate of PV sera in IIF using RBE as substrate and the diagnostic usefulness of the aforementioned test.

Methods

Patients diagnosed with PV presenting to Razi Hospital, Tehran, Iran, were recruited. The patients' demographics, disease severity, and response to the initial treatment were recorded. Sera were collected and tested by IIF on RBE and by desmoglein 3/1 (Dsg 3/1) enzyme-linked immunosorbent assay. Patients were followed up closely for a mean of 53.9 months for any evidence of malignancy.

Results

Forty-six patients were enroled (mean age of 42.9 years old, 31 females). Nine sera (19.6%) showed reactivity in IIF on RBE. Mean serum anti-Dsg levels did not differ significantly among the two groups with positive and negative IIF results. Negative anti-Dsg3 was related to a higher positive rate in IIF on RBE. There was no significant correlation between the reactivity of IIF on RBE and patients' demographic, clinical, or serological characteristics.

Conclusions

IIF on RBE is a sensitive test for detecting antibodies against plakins. However, it has a relatively high false-positive rate in PV, probably due to the epitope spreading phenomenon. This test should be suggested when there is a clinical or immunohistopathological suspicion of PNP and should be interpreted with caution.

Paraneoplastic Pemphigus Autoantibodies Against C-terminus of Desmoplakin Induced Acantholysis In Vitro and In Vivo

Paraneoplastic pemphigus (PNP) is an autoimmune bullous disease associated with underlying neoplasms and characterized by antibodies against desmoglein 3 (Dsg 3) and plakins. Autoantibodies against desmoglein 3 in sera of patients with PNP have been proven to cause acantholysis in vivo in neonatal mice. As a member of the plakin family, autoantibodies against desmoplakin were detected frequently by immunoprecipitation in the sera of PNP. The recombinant C-terminus of desmoplakin was expressed and purified to adsorb the specific autoantibodies against the C-terminus of desmoplakin. In vitro dispase-dependent keratinocyte dissociation assay and in vivo IgG passive transfer into neonatal mice assay were performed, followed by the electronic microscopy examination and TUNEL assay. We found that anti-C terminus of desmoplakin autoantibodies caused blisters and acantholysis in mice skin at a dose-dependent manner. Moreover, dissociated fragments were observed after incubation with the purified IgG against desmoplakin, compared with normal human IgG (P-value =0.0207). The electronic microscopy examination showed the disconnection of keratin intermediate filaments from desmosomes. Lastly, apoptosis of keratinocytes in the TUNEL assay was all detected in the skins of neonatal mice after injection of the anti-C terminus of desmoplakin autoantibodies. Taken together, the study suggests that autoantibodies against the C-terminus of desmoplakin might be pathogenic in PNP.

Erythema multiforme associated with anti-plakin antibodies: a multicentric retrospective case series

BACKGROUND

Erythema multiforme (EM) is a muco-cutaneous inflammatory disease mainly triggered by herpes simplex virus (HSV) recurrences. Association of EM and circulating auto-antibodies against plakins (anti-PLK-Abs [EM-PLK+]) has been reported. However, little is known about this subset of EM.

OBJECTIVES

We aimed to describe the clinical and immunological features and response to treatment of EM-PLK+.

METHODS

We conducted a retrospective multicentric study of EM-PLK+ selected from the database of the immunological laboratory of Bichat hospital, Paris, France, from January 2009 to December 2020. Anti-PLK-Abs were detected in ≥1 immunological tests: immunofluorescence assay, immunoblotting and/or ELISA. Patients with alternative diagnoses were excluded.

RESULTS

We included 29 patients (16 women, median age 25 [range 2-58] years). EM-PLK+ were mostly major (EM with ≥2 mucosal involvements; n = 24, 83%) and relapsing (≥2 flares; n = 23, 79%). Cutaneous lesions were target (n = 13, 54%) and target-like lesions (n = 9, 38%) with usual topography (acral, n = 19, 79%; limbs, n = 21, 88%). Mucosal lesions affected the mouth (n = 27, 96%) and genitalia (n = 19, 68%), with a median of 2 [range 0-5] mucous membranes. EM-PLK+ were suspected as certain or possible postherpetic (EM-HSV) in 19 cases (65.5%); no triggering factors were detected in 9 (31%) patients. Desmoplakin-I/II Abs were the most frequent anti-PLK-Abs (n = 20, 69%); envoplakin and periplakin Abs were detected in 11 and 9 cases. Relapsing EM-PLK+ (n = 23) were still active (≥1 flare within 6 months) in 13 (57%) patients despite immunosuppressive therapy (n = 8, 62%). Antiviral drugs were ineffective in preventing relapse in 15/16 (94%) EM-HSV.

CONCLUSION

The rationale for anti-PLK-Ab detection in EM is not elucidated. More systematic research of anti-PLK-Abs is warranted to better understand whether this association reflects humoral immune activity in a subset of EM or is fortuitous, related to an epitope spreading process. However, EM-PLK+ seems to be associated with major and relapsing subtypes, and difficult-to-treat cases.

Pattern-Specific Loss of Desmoplakin I and II Immunoreactivity in Erythema Multiforme and its Variants: A Possible Aid in Histologic Diagnosis

Erythema multiforme (EM), Stevens-Johnson syndrome (SJS), and toxic epidermal necrolysis (TEN) comprise a family of mucocutaneous diseases associated with significant morbidity and mortality. Previous studies have confirmed the presence of autoantibodies to desmoplakin (Dp) I and II in patients with EM, SJS, and TEN. Truncated Dp production leads to characteristic changes visible on light microscopy: perinuclear clumping of keratin filaments and dyskeratotic keratinocyte. Based on these observations, the question arises as to whether a loss of Dp immunoreactivity in skin biopsies could serve as a diagnostic marker of EM, SJS, and TEN. This study analyzed Dp immunostaining patterns in 20 patients with EM or SJS/TEN. To assess the specificity of this approach, Dp immunostaining was also performed on specimens from patients with 5 potential histologic mimics of EM, SJS, and TEN. All of the samples from patients with EM, SJS, and TEN demonstrated absent or markedly diminished staining for Dp. A χ test demonstrated a statistically significant difference between the staining patterns in EM, SJS, and TEN and each of the other diagnostic groups that were investigated. This is the first report demonstrating statistically significant specificity of Dp staining patterns in EM/SJS/TEN as compared with other interface dermatitides.

From HSV infection to erythema multiforme through autoimmune crossreactivity

Scientific and clinical data indicate that human herpes simplex virus 1 (HSV1) and, at a lesser extent, human herpes simplex virus 2 (HSV2) are factor(s) implicated in the development of erythema multiforme (EM). With a focus on oral EM, the present structured review of proteomic and epitope databases searched for the molecular basis that might link HSV1 and HSV2 infections to EM. It was found that a high number of peptides are shared between the two HSVs and human proteins related to the oral mucosa. Moreover, a great number of the shared peptides are also present in epitopes that have been experimentally validated as immunopositive in the human host. The results suggest the involvement of HSV infections in the induction of oral EM via a mechanism of autoimmune cross-reactivity and, in particular, highlight a potential major role for 180kDa bullous pemphigoid antigen and HSV1 infection in the genesis of crossreactions potentially conducive to EM.

Desmosomes in acquired disease

Desmosomes are cell-cell junctions that mediate adhesion and couple the intermediate filament cytoskeleton to sites of cell-cell contact. This architectural arrangement integrates adhesion and cytoskeletal elements of adjacent cells. The importance of this robust adhesion system is evident in numerous human diseases, both inherited and acquired, which occur when desmosome function is compromised. This review focuses on autoimmune and infectious diseases that impair desmosome function. In addition, we discuss emerging evidence that desmosomal genes are often misregulated in cancer. The emphasis of our discussion is placed on the way in which human diseases can inform our understanding of basic desmosome biology and in turn, the means by which fundamental advances in the cell biology of desmosomes might lead to new treatments for acquired diseases of the desmosome.

Identification of periplakin as a new target for autoreactivity in idiopathic pulmonary fibrosis

RATIONALE

Injury to alveolar epithelial cells is central to the pathophysiology of idiopathic pulmonary fibrosis (IPF). An abnormal autoimmune response directed against antigens of the alveolar epithelium may contribute to the disease.

OBJECTIVES

To detect circulating autoantibodies (autoAbs) directed against epithelial structures.

METHODS

We performed immunoblot by separating human placental amnion extract or alveolar epithelial cell (A549 cell line) proteins on polyacrylamide gels, blotting on nitrocellulose membranes, and incubating with serum from patients with IPF (n = 40) or healthy subjects (n = 40). Proteomic analysis and mass spectrometry characterized the target protein. Inhibition experiments performed with the correspondent recombinant protein confirmed our results.

MEASUREMENTS AND MAIN RESULTS

We identified IgG autoAbs recognizing a 200-kD protein in the serum of patients with IPF. Proteomic analysis identified this protein as human periplakin (PPL), a component of desmosomes. Anti-PPL Abs were found by immunoblot in both serum and bronchoalveolar lavage in patients with IPF: 16/40 (40%) of them were positive versus none of the control subjects. Immunohistochemistry revealed that PPL was strongly expressed in bronchial and alveolar epithelium, but that PPL exhibited changes in intracellular localization among normal and fibrotic alveolar epithelium. In an alveolar epithelial wound repair assay, an anti-PPL IgG decreased cell migration. Recombinant PPL induced bronchoalveolar lavage T lymphocyte proliferation. Patients with IPF with anti-PPL Abs had a more severe respiratory disease, despite no difference in survival.

CONCLUSIONS

We found a new circulating autoAb directed against PPL in patients with IPF, associated with a more severe disease.

Antiplectin autoantibodies in subepidermal blistering diseases

BACKGROUND

Hemidesmosomal proteins may become targets of autoimmunity in subepidermal blistering diseases. Well-known recognized autoantigens are the intracellular plaque protein BP230, the transmembrane BP180 and its shed ectodomain LAD-1.

OBJECTIVES

To establish the prevalence of autoimmunity against plectin, another intracellular plaque protein, and to investigate its antigenic sites.

METHODS

Two hundred and eighty-two patients with subepidermal blistering diseases, investigated by routine immunoblot analysis for possible antiplectin antibodies, were included in the study. Epitope mapping was performed using recombinantly produced overlapping plectin domains from the actin-binding domain to the rod domain. The COOH-terminal region of plectin was not included in the study.

RESULTS

In 11 of 282 (3.9%) patients an immunoblot staining pattern identical to that of antiplectin monoclonal antibody HD121 was found. Affinity-purified antibodies bound back to normal human skin in a pattern typical for plectin, i.e. to the epidermal basement membrane zone as well as to keratinocytes in the epidermis, and to myocytes. No binding was seen to plectin-deficient skin of a patient with epidermolysis bullosa simplex with muscular dystrophy. Epitope mapping of the plectin molecule showed that the central coiled-coil rod domain is an immunodominant hotspot as 92% of the sera with antiplectin antibodies reacted with it. Most patients with antiplectin antibodies also had antibodies to other pemphigoid antigens.

CONCLUSIONS

Plectin is a minor pemphigoid antigen with an immunodominant epitope located on the central rod domain.

Erythema multiforme and related disorders

Erythema multiforme (EM) and related disorders comprise a group of mucocutaneous disorders characterized by variable degrees of mucosal and cutaneous blistering and ulceration that occasionally can give rise to systemic upset and possibly compromise life. The clinical classification of these disorders has often been variable, thus making definitive diagnosis sometimes difficult. Despite being often caused by, or at least associated with, infection or drug therapy, the pathogenic mechanisms of these disorders remain unclear, and as a consequence, there are no evidence-based, reliably effective therapies. The present article reviews aspects of EM and related disorders of relevance to oral medicine clinical practice and highlights the associated potential etiologic agents, pathogenic mechanisms and therapies.

Sera from patients with toxic epidermal necrolysis contain autoantibodies to periplakin

BACKGROUND

The pathophysiological mechanism of toxic epidermal necrolysis (TEN) with extensive bullae that is induced suddenly by drugs is not well understood. The individual patterns and distribution of the widespread mucocutaneous reactions of TEN often show striking similarities with those of paraneoplastic pemphigus (PNP), which is known to involve autoantibodies (aAbs) to members of the plakin family.

OBJECTIVES

To investigate the existence of circulating aAbs to periplakin in the sera of patients with TEN.

METHODS

The presence of circulating aAbs to periplakin was examined using immunoblotting, immunoabsorption and indirect immunofluorescence (IF) analyses. Recombinant protein expression was used to determine the interaction between periplakin and aAbs in the sera of patients with TEN.

RESULTS

Indirect IF studies revealed circulating aAbs in the intercellular area in the epidermis. Interestingly, on rat bladder the staining pattern of the IgG deposits was similar to that observed in patients with PNP. Immunoblotting analysis of the epidermal extracts was used to identify the aAbs in the sera of patients with TEN. These contained circulating aAbs to a 190-kDa protein corresponding to periplakin. Recombinant periplakin and domains of periplakin were prepared in order to confirm the existence of aAbs to periplakin. Immunoblotting with these proteins demonstrated that the sera from patients with TEN reacted with each domain as well as with the full-length periplakin.

CONCLUSIONS

We found that circulating aAbs in the sera of patients with TEN target periplakin. These aAbs might play a role in the pathogenesis of TEN as a humoral autoimmune mechanism.

Enzyme-linked immunosorbent assay for detection of peptide-specific human antidesmoplakin autoantibodies

BACKGROUND

Autoantibodies directed against desmoplakin (Dp) I and II have recently been characterized in a subset of patients with severe erythema multiforme (EM), a recurrent inflammatory skin disease with a broad spectrum of clinical manifestations. These autoantibodies recognize a peptide epitope localized within the extreme end of the carboxy terminal domain of Dp responsible for the assembly of keratin filaments to the desmosomal plaque. Using dot blot analysis with overlapping synthetic peptides, the binding epitope YSYSYS has been identified.

OBJECTIVES

To establish an enzyme-linked immunosorbent assay (ELISA) for detection of peptide-specific anti-Dp autoantibodies in sera of patients with EM.

METHODS

A synthetic peptide containing the respective amino acid sequence was used as matrix for ELISA plates. Serum samples from patients with known EM and peptide-specific anti-Dp autoantibodies verified by immunoblotting, immunoprecipitation and epitope mapping were used.

RESULTS

Establishing an index value of 42.0, 25 of 25 serum samples from five patients with peptide-specific anti-Dp autoantibodies were positive in the ELISA. From control sera, none of 31 bullous disease sera and only one (1.2%) of 83 normal human sera were positive.

CONCLUSIONS

These data show that the ELISA presented in this study represents a sensitive and highly specific tool for the detection of peptide-specific anti-Dp autoantibodies in patients with EM.

Expression of FcRn, the MHC class I-related receptor for IgG, in human keratinocytes

The neonatal Fc receptor (FcRn) for IgG has been shown to be responsible for IgG transport and to be involved in IgG catabolism. In this study, we show expression of FcRn in normal human epidermal keratinocytes. By RT-PCR, we demonstrate the FcRn alpha-chain mRNA obtained from cultured keratinocytes creating a 457 bp product as confirmed by sequence analysis. Northern blot analysis shows a 1.5 kb transcript. Real-time PCR reveals consistent expression of FcRn alpha-chain mRNA in human keratinocytes from different donors. Anti-FcRn alpha2-extracellular domain and anti-FcRn cytoplasmic tail antibody (Ab) directed against defined antigenic targets were generated and used for immunoblotting and immunoprecipitation revealing protein expression of the 46 kDa FcRn alpha-chain. By immunofluorescence microscopy, we find granular-vesicular staining for FcRn alpha-chain in keratinocytes. Fluorescence-activated cell sorting analysis gives predominantly an intracellular distribution of FcRn in keratinocytes. Biochemically, we demonstrate Fc-dependent binding of human IgG at acidic pH. In normal human epidermis, we find a cytoplasmic vesicular staining of predominantly basal and suprabasal keratinocytes. In summary, we demonstrate expression of a functional FcRn in normal human epidermal keratinocytes. These findings further emphasize the role of keratinocytes as immunomodulating cells in inflammatory and immunologic processes of the skin.

Development of antigen-specific ELISA for circulating autoantibodies to extracellular matrix protein 1 in lichen sclerosus

Lichen sclerosus is a common, acquired chronic inflammatory skin disease of unknown etiology, although circulating autoantibodies to the glycoprotein extracellular matrix protein 1 (ECM1) have been detected in most patients' sera. We have examined the nature of ECM1 epitopes in lichen sclerosus sera, developed an ELISA system for serologic diagnosis, and assessed clinicopathological correlation between ELISA titer and disease. Epitope-mapping studies revealed that lichen sclerosus sera most frequently recognized the distal second tandem repeat domain and carboxyl-terminus of ECM1. We analyzed serum autoantibody reactivity against this immunodominant epitope in 413 individuals (95 subjects with lichen sclerosus, 161 normal control subjects, and 157 subjects with other autoimmune basement membrane or sclerosing diseases). The ELISA assay was highly sensitive; 76 of 95 lichen sclerosus patients (80.0%) exhibited IgG reactivity. It was also highly specific (93.7%) in discriminating between lichen sclerosus and other disease/control sera. Higher anti-ECM1 titers also correlated with more longstanding and refractory disease and cases complicated by squamous cell carcinoma. Furthermore, passive transfer of affinity-purified patient IgG reproduced some histologic and immunopathologic features of lichen sclerosus skin. This new ELISA is valuable for the accurate detection and quantification of anti-ECM1 autoantibodies. Moreover, the values may have clinical significance in patients with lichen sclerosus.

RPE65 of Retinal Pigment Epithelium, A Putative Receptor Molecule for Plasma Retinol-Binding Protein, is Expressed in Human Keratinocytes

Retinoids are important modulators for cell growth and differentiation of normal skin. In plasma, retinol is transported coupled to plasma retinol-binding protein. In this study, we investigated gene and protein expression of RPE65, a putative receptor for plasma retinol-binding protein in human epidermal keratinocytes. We performed real-time PCR analysis to evaluate expression of RPE65 mRNA in proliferating and differentiating keratinocytes. Immunoblotting with anti-RPE65 antibody shows distinct reactivity to a 61-kDa protein. Indirect immunofluorescence on normal human epidermis reveals cell surface labeling of keratinocytes. Laser scan microscopy exhibits colocalization of plasma retinol-binding protein and RPE65 on cultured keratinocytes. Internalization experiments with [3H]retinoic acid-retinol-binding protein complex in the presence and absence of excess of retinol-binding protein indicates receptor-dependent uptake of retinoids. We further show isolation of RPE65 protein by affinity chromatography from lysates of keratinocytes using a retinol-binding protein-matrix gel column. In summary, we demonstrate mRNA and protein expression of RPE65 in epidermal keratinocytes. Colocalization of plasma retinol-binding protein with RPE65 and affinity binding suggest a direct interaction of RPE65 with plasma retinol-binding protein in cultured human keratinocytes that might be involved in retinoid uptake of keratinocytes.

Internalization via plasmalemmal vesicles: a route for antidesmoplakin autoantibodies into cultured human keratinocytes

Recently, autoantibodies to desmoplakin I and II have been identified in a subset of patients with a severe form of erythema multiforme. These autoantibodies recognize a specific peptide sequence at the carboxy terminal domain of desmoplakin I and II responsible for interaction with keratin filaments. Desmoplakins are major constitutive proteins of the inner dense desmosomal plaque of keratinocytes and are entirely localized within the cells. With the assumption of pathogenecity for circulating autoantibodies, the question arose how antidesmoplakin autoantibodies enter keratinocytes. Utilizing immunhistochemical procedures for cell motility and time kinetic studies at the light- and electron-microscopic level, we found that autoantibodies are bound at the cell surface of cultured human keratinocytes, internalized via plasmalemmal vesicles, and are found consecutively within tubulovesicular structures inside the cells. At the same time, a fraction of antibodies can be detected at the inner dense desmosomal plaques. Immunogold labeling reveals internalization of autoantibodies in small non-coated plasmalemmal vesicles positive for caveolin. These observations indicate that vesicular transport may represent a relevant biological mechanism for antidesmoplakin autoantibodies to enter keratinocytes and allow access to their corresponding antigenic target in vivo.

RasGAP-like protein IQGAP1 is expressed by human keratinocytes and recognized by autoantibodies in association with bullous skin disease

Autoantibodies in patients with autoimmune bullous skin diseases, such as pemphigus or bullous pemphigoid are of diagnostic value and might play a part in the pathogenic scenario. In this study we present five patients with erythematous plaques, subepidermal blister formation of the skin, and the presence of circulating autoantibodies directed against a so far unrecognized 190 kDa antigen in human keratinocytes. Amino acid sequence analysis identified the protein as IQGAP1, a recently described human Ras GTPase-activating-like protein suspected to act as an effector molecule for Cdc42 and Rac1, members of the Rho small GTPase family and to play a key part in regulating E-cadherin-mediated cell adhesion. The protein is selectively recognized by a monoclonal anti-IQGAP1 antibody on western blots and immunoprecipitates from keratinocyte extracts. Indirect immunofluorescence locates IQGAP1 within individual keratinocytes in a cytoplasmic pattern and along the cell periphery at adhesive sites. Our results demonstrate IQGAP1, a newly described multifunctional protein, to be constitutively expressed in human keratinocytes where it may contribute to the integrity of the epidermal layer. Furthermore, we found autoantibodies reacting with IQGAP1 in patients with bullous skin eruptions most apparently belonging to the spectrum of bullous pemphigoid.

Oral and genital lichenoid reactions associated with circulating autoantibodies to desmoplakins I and II: a novel target antigen or example of epitope spreading?

We describe the first reported case of persistent oral and genital lichenoid reactions associated with circulating antibodies to 250- and 215-kd proteins, compatible with desmoplakin I and II, respectively. We discuss the potential role of epitope spreading, leading to the novel development of specific autoantibodies to desmoplakin.

Organotypic keratinocyte coculture using normal human serum: an immunomorphological study at light and electron microscopic levels

Organotypic human skin equivalents of keratinocytes and fibroblasts embedded in collagen matrix have been the subject of studies dealing with various culture conditions. Development of standardized living skin equivalents using defined culture media containing respective supplements can provide important instruments of investigation in skin biology. In addition, tissue engineering has created human skin substitutes for treatment of acute and chronic wounds. In our study, we generate a modified organotypic human skin equivalent using normal human serum instead of fetal calf serum (FCS). This living skin equivalent shows regular stratification of the epidermis and the dermal-epidermal junction zone at the light and electron microscopic level after 1 and 3 weeks of coculture. Indirect immunofluorescence reveals regular expression of differentiation antigens and the major structural proteins collagen IV, laminin 5 and the integrin chains alpha 6 and beta 4 at the dermo-epidermal junction zone. Immunoelectron microscopy demonstrates expression of collagen IV, alpha 6 and beta 4 integrin after 1 and 3 weeks of coculture. This organotypic skin model could be the basis for autologous skin grafting for acute or chronic wounds using autologous serum as well as patients' keratinocytes and fibroblasts, thus minimizing the risk of transmitting infectious agents.

Characterization of a monoclonal antibody against desmoplakin 1 for use in dogs

Skin biopsy specimens from face, axilla, abdomen and thigh, mucocutaneous tissues from anus and vagina, and oral mucosa from six healthy Beagle dogs were examined for desmoplakin (Dsp) immunoreactivity using immunoblotting and immunohistochemical analysis. With immunoblotting using mouse antihuman Dsp 1 monoclonal antibody (DP2.17), a band was detected at 250 kDa in all the extracts as in normal human skin samples, although no band was detected at 210 kDa, suggesting that monoclonal antibody DP2.17 recognizes canine Dsp 1 but not Dsp 2. Moreover, the desmosome regions of all specimens were stained with DP2.17 using immunohistochemical analysis. From these results, DP2.17, developed for the examination of human skin, might be suitable for the investigation of Dsp-related skin disorders in dogs.

Sensitivity and specificity of clinical, histologic, and immunologic features in the diagnosis of paraneoplastic pemphigus

BACKGROUND

Paraneoplastic pemphigus (PNP) is an autoimmune blistering disease characterized by the production of autoantibodies mainly directed against proteins of the plakin family. An overlapping distribution of autoantibody specificities has been recently reported between PNP, pemphigus vulgaris (PV), and pemphigus foliaceus (PF), which suggests a relationship between the different types of pemphigus.

OBJECTIVE

Our purpose was to evaluate the sensitivity and the specificity of clinical, histologic, and immunologic features in the diagnosis of PNP.

METHODS

The clinical, histologic, and immunologic features of 22 PNP patients were retrospectively reviewed and compared with those of 81 PV and PF patients without neoplasia and of 8 PV and 4 PF patients with various neoplasms.

RESULTS

One clinical and 2 biologic features had both high sensitivity (82%-86%) and high specificity (83%-100%) whatever the control group considered: (1) association with a lymphoproliferative disorder, (2) indirect immunofluorescence (IIF) labeling of rat bladder, and (3) recognition of the envoplakin and/or periplakin bands in immunoblotting. Two clinicopathologic and two biologic features had high specificity (87%-100%) but poor sensitivity (27%-59%): (1) clinical presentation associating erosive oral lesions with erythema multiforme-like, bullous pemphigoid-like, or lichen planus-like cutaneous lesions; (2) histologic picture of suprabasal acantholysis with keratinocyte necrosis, interface changes, or lichenoid infiltrate; (3) presence of both anti-epithelial cell surface and anti-basement membrane zone antibodies by IIF; and (4) recognition of the desmoplakin I and/or BPAG1 bands in immunoblotting. Interestingly, 45% of patients with PNP presented initially with isolated oral erosions that were undistinguishable from those seen in PV patients, and 27% had histologic findings of only suprabasal acantholysis, which was in accordance with the frequent detection of anti-desmoglein 3 antibodies in PNP sera.

CONCLUSION

The association with a lymphoproliferative disorder, the IIF labeling of rat bladder, and the immunoblotting recognition of envoplakin and/or periplakin are both sensitive and specific features in the diagnosis of PNP.

A paraneoplastic mixed bullous skin disease: breakdown in tolerance to multiple epidermal antigens

We report a new type of paraneoplastic mixed bullous skin disease in a patient with a B-cell lymphoma associated with monoclonal IgM kappa paraproteinaemia. The patient's clinical and histological features were reminiscent of bullous pemphigoid. Characterization of antiepidermal antibodies by immunoblotting and indirect immunoelectron microscopy demonstrated a novel pattern of reactivity: IgG antibodies were directed against desmoplakins I-II and BPAG2, and were associated with antidesmoglein 3 polyclonal IgM antibodies. Such an autoreactive pattern involving antidesmoplakins, anti-BPAG2 and antidesmoglein 3 antibodies has not been previously reported. It reflects the breakdown of tolerance to multiple epidermal antigens observed in some patients with malignancy.

Analysis of the desmoplakin gene reveals striking conservation with other members of the plakin family of cytolinkers

Members of the plakin family of cytolinker proteins integrate filaments into cellular networks and anchor these networks to the plasma membrane. Their importance is supported by the existence of cell and tissue fragility disorders caused by mutations in certain family members. In this study, the human gene encoding desmoplakin (DSP) was characterized and its structure compared with the related family members: plectin, bullous pemphigoid antigen 1 (BPAG1), envoplakin (EVPL) and periplakin (PPL). Sequence analysis of genomic clones was carried out in combination with a PCR-based strategy to define intron-exon borders. DSP was mapped using the GB4 radiation hybrid mapping panel to the interval between markers D6S296 and AFM043 x f2, corresponding to cytogenetic band 6p24. In addition, the murine gene (Dsp) was mapped to mouse chromosome 13 by interspecific backcross mapping. DSP encompasses approximately 45 kb organized into 24 exons and 23 introns, and the pattern of intron-exon borders bears a striking resemblance to other members of the plakin family. Notable features include the fact that a single large exon encodes the entire C-terminus of each gene. In contrast, the N-termini comprise numerous smaller exons with conservation of many intron-exon borders. Detailed characterization and mapping of these genes will facilitate their further evaluation as targets of genetic disorders and provide insights into the evolutionary relationships among molecules in this emerging gene family.

Update on immunoelectron microscopy in diagnostic dermatopathology and cutaneous biology

Immunoelectron microscopy for diagnostic dermatopathology is hardly ever necessary. Immunoelectron microscopy, however, is very helpful in the work-up of interesting cases, for the study of genetic and autoimmune bullous diseases and for basic science studies, particularly in conjunction with molecular biology techniques. It is also very helpful for investigators requiring double labeling.