IgG Anti-basement Membrane Autoantibodies Research Articles

Differentiating antiepiligrin cicatricial pemphigoid from epidermolysis bullosa acquisita by indirect immunofluorescence of skin substrates lacking Type VII collagen or laminin 332: a case report and review of literature

Antiepiligrin cicatricial pemphigoid (AECP) is a chronic autoimmune subepidermal blistering disease characterized by clinical features of cicatricial pemphigoid and circulating IgG antibasement membrane autoantibodies directed against laminin 332. There is growing evidence of an increased relative risk for solid cancers and lymphomas in AECP patients, especially in the 1 st year after the onset of blisters. However, it is difficult to distinguish patients with initially skin-predominant AECP from similar findings of epidermolysis bullosa acquisita merely based on clinical, histopathologic, and immuno-pathologic examinations. This is a report on a case of AECP confirmed by indirect immunofluorescence of type VII collagen- and laminin 332-deficient skin as substrates to differentiate it from epidermolysis bullosa acquisita.

Two Cases of Anti-Epiligrin Cicatricial Pemphigoid With and Without Associated Malignancy

Anti-epiligrin cicatricial pemphigoid (AECP) is a chronic, mucous membrane-dominated, subepithelial blistering disease characterized by circulating anti-basement membrane zone auto-antibodies to laminin 5. Recent studies have shown that people with AECP have an increased relative risk for malignant tumours. In this report we describe two patients with AECP. In both cases, indirect immunofluorescence demonstrated circulating IgG anti-basement membrane auto-antibodies that bound to the dermal side of 1M NaCl split normal skin. Immunoblotting using laminin 5 purified from keratinocyte extract as a substrate showed that the IgG antibodies of patient 1 reacted with the 140-kDa beta3 subunit of laminin 5 and IgG antibodies of patient 2 reacted with the 165-kDa and 145-kDa alpha3 subunits. Patient 1 had prostate carcinoma and his blistering was resistant to therapy. Patient 2 had no detectable malignancy and treatment with doxycycline was successful.

Anti-epiligrin cicatricial pemphigoid: clinical findings, immunopathogenesis, and significant associations.

We report the clinical and immunopathologic findings in a cohort of 35 patients with anti-epiligrin cicatricial pemphigoid (AECP). These patients have a mucosal predominant subepithelial blistering disease that is clinically indistinguishable from other forms of cicatricial pemphigoid. The mucosal surfaces of the mouth and eye are most commonly involved. The skin is also involved in most patients, but usually this is less severe than mucosal involvement. AECP is characterized by the binding of circulating IgG autoantibodies to the dermal side of 1M NaCl split human skin on indirect immunofluorescence microscopy. These IgG antibasement membrane autoantibodies target laminin 5, a heterotrimeric protein consisting of alpha3, beta3, and gamma2 subunits. IgG autoantibodies predominantly target the G domain within the alpha subunit. The presence of circulating IgG autoantibodies are specific for the diagnosis of AECP and are not seen in patients with other autoimmune blistering diseases or normal volunteers. Furthermore, we expand on data previously reported on the finding of an increased relative risk for solid cancer in patients with AECP, especially in the first year after blister onset. The majority of cancers documented in a cohort of 35 patients assembled over 12 years of study were adenocarcinomas that were at an advanced stage at their time of detection. This circumstance is thought to account for a high incidence of mortality among AECP patients who develop an associated cancer. AECP patients also demonstrate a significant risk for mortality as a consequence of treatment with systemic immunosuppressives. The current longitudinal study suggests that only a minority of AECP patients go into remission.

Treatment of epidermolysis bullosa acquisita with the humanized anti-Tac mAb daclizumab.

Epidermolysis bullosa acquisita (EBA) is an autoimmune subepidermal blistering disease characterized by IgG anti-basement membrane autoantibodies to collagen VII. Since autoantibody formation in EBA patients is thought to be T-cell-dependent, the degree of T cell activation in three patients (all males, ages 33-44 years) was assessed by quantitation of soluble Tac, a fragment of the alpha-subunit of the high-affinity IL-2 receptor (CD25). Soluble Tac levels in all patients were elevated [highest random values, 2430, 920, and 560 IU/ml (normal range, 112-502)]. Based on such findings, these patients were treated with the humanized murine monoclonal anti-Tac antibody daclizumab (1 mg/kg, 6-12 iv treatments at 2- to 4-week intervals). All patients had a significant, rapid, and persistent decrease in lymphocyte CD25 expression. Though a moderate decrease in lymphocyte expression of 7G7, an IL-2 receptor epitope not bound by daclizumab, was noted, stable levels of CD3 cells and in vitro saturation studies indicated that daclizumab effectively bound CD25 and did not promote clearance of such cells from peripheral blood. There were no complications and no patient developed antibodies against daclizumab. While no apparent clinical benefit was seen in two patients with dermolytic disease, one patient with inflammatory EBA had a favorable response. While on daclizumab, this patient stopped prednisone, significantly reduced dapsone, and improved clinically. Furthermore, his disease flared when treatment was stopped, and resumption of daclizumab again effected improvement within 2 weeks. Daclizumab therapy is safe and well tolerated in EBA patients. It may be effective as a corticosteroid sparing agent in patients with inflammatory EBA.

IgG autoantibodies in patients with anti-epiligrin cicatricial pemphigoid recognize the G domain of the laminin 5 alpha-subunit.

Anti-epiligrin cicatricial pemphigoid (AECP) is a mucosal-predominant, subepithelial blistering disease characterized by IgG anti-basement membrane autoantibodies to laminin 5 (alpha3beta3gamma2). This and prior studies found that autoantibodies from most patients recognize the alpha-subunit of this laminin isoform. Accordingly, sera from 10 representative patients were tested against prokaryotic recombinants of this polypeptide in epitope mapping studies. cDNAs spanning the full length of the alpha-subunit were generated by PCR, directionally cloned into the pGEX-4T-3 vector, and expressed as glutathione-S-transferase fusion proteins of appropriate size and immunoreactivity. Sera from 9 of 10 AECP patients immunoblotted fusion proteins corresponding to subdomains G2, G3, G4, and G5 at the carboxyl terminus of the laminin 5 alpha-subunit. Serum from 1 patient (and that from normal volunteers) showed no reactivity to any fusion proteins; no sera bound recombinant glutathione-S-transferase alone. Immunoadsorption of patient sera with fusion proteins corresponding to the G domain substantially reduced basement membrane autoantibody titers. IgG from patients with this form of cicatricial pemphigoid recognize the portion of laminin 5 thought to play a key role in promoting keratinocyte adhesion to epidermal basement membrane.

Human Anti-Laminin 5 Autoantibodies Induce Subepidermal Blisters in an Experimental Human Skin Graft Model

Patients with one form of cicatricial pemphigoid have IgG antibasement membrane autoantibodies against laminin 5 (alpha3beta3gamma2). Although passive transfer of rabbit anti-laminin 5 IgG to neonatal mice has been shown to induce subepidermal blisters that mimic those in patients, it has not been possible to directly assess the pathogenic activity of human autoantibodies in this animal model because the latter do not bind murine skin. To address this question, a disease model in adult mice as well as SCID mice bearing human skin grafts was developed. Adult BALB/C mice challenged with rabbit anti-laminin 5 IgG developed, in a concentration-related fashion, erythema, erosions, and crusts surrounding injection sites, histologic evidence of noninflammatory, subepidermal blisters, and deposits of rabbit IgG and murine C3 in epidermal basement membranes. Anti-laminin 5 IgG also induced subepidermal blisters in: adult complement-, mast cell-, and immuno-deficient mice; adult BALB/C mice pretreated with dexamethasone; and human skin grafts on SCID mice. Alterations did not develop in matching controls challenged with identical amounts of purified normal rabbit IgG or bovine serum albumin. Using this adult mouse model, human skin grafts on SCID mice were challenged with purified IgG from patients with alpha subunit-specific, anti-laminin 5 autoantibodies, or normal controls. Patient (but not control) IgG induced epidermal fragility as well as noninflammatory, subepidermal blisters in grafted human (but not adjacent murine) skin. Moreover, whereas all mice that received patient autoantibodies had anti-laminin 5 IgG in their circulation, deposits of human IgG were present only in the epidermal basement membranes of grafts. Interestingly, these in situ and circulating autoantibodies were predominately of the IgG4 subclass. These studies demonstrate that human anti-laminin 5 autoantibodies are pathogenic in vivo and describe an animal model that can be used to define disease pathomechanisms and biologically important domains within this autoantigen.

Reactivity of autoantibodies from patients with defined subepidermal bullous diseases against 1 mol/L salt-split skin: Specificity, sensitivity, and practical considerations

Background: Circulating IgG anti-basement membrane autoantibodies from patients with subepidermal bullous diseases can be categorized on the basis of their pattern of reactivity against 1 mol/L sodium chloride (NaCl)-split skin. Objective: The purpose of this study was to define by immunochemical techniques the specific antigen(s) targeted by IgG autoantibodies from a group of patients with subepidermal blistering diseases and then (1) prospectively determine which side(s) of 1 mol/L NaCl-split skin is (are) bound by these patients' autoantibodies, (2) compare the sensitivity of intact and 1 mol/L NaCl-split skin for the detection of these autoantibodies; and (3) devise a practical method to distinguish patients with antiepiligrin cicatricial pemphigoid from those with other subepidermal blistering diseases. Methods: Investigative techniques included direct and indirect immunofluorescence microscopy, immunoprecipitation studies, and immunoblotting. Results: These studies identified 14 patients whose sera immunoprecipitate bullous pemphigoid antigens 1, 2, or both. These patients' circulating IgG anti-basement membrane autoantibodies bind the epidermal ( n = 11), epidermal and dermal ( n = 2), or dermal ( n = 1) sides of 1 mol/L NaCl-split skin by indirect immunofluorescence microscopy. In contrast, IgG from all patients with autoantibodies directed against type VII collagen ( n = 5) or epiligrin ( n = 6) bind only the dermal side of 1 mol/L NaCl-split skin. In all but one patient in this series, 1 mol/L NaCl-split skin proved to be a more sensitive test substrate than intact human skin for detection of circulating IgG anti-basement membrane autoantibodies. Patients with antiepiligrin cicatricial pemphigoid were distinguished from other patients in that their circulating autoantibodies bound epidermal basement membrane in the skin of primates but not small mammals. Conclusion: NaCl-split skin (1 mol/L) of various species is a sensitive and practical indirect immunofluorescence microscopy test substrate for the evaluation of patients with IgG anti-basement membrane autoantibodies and evaluation of subepidermal bullous diseases.

Linear IgA bullous dermatosis. Characterization of a subset of patients with concurrent IgA and IgG anti-basement membrane autoantibodies.

The term linear IgA bullous dermatosis defines an immune-mediated blistering skin disease characterized by pruritic blisters, subepidermal separation with neutrophilic infiltration, and linear IgA antibody deposition at the basement membrane zone (BMZ). However, some patients with linear IgA bullous dermatosis demonstrate both IgA and IgG anti-BMZ autoantibodies on immunofluorescence. We describe four such patients and attempt to define this group of patients by studying their clinical, histopathologic, immunopathologic, immunoultrastructural, and immunochemical characteristics. Clinically, all four patients had a generalized pruritic blistering skin disease consistent with linear IgA bullous dermatosis. Histopathologically, all four cases demonstrated subepidermal blister formation with a predominantly neutrophilic dermal infiltrate. Immunopathologically, tissue-bound IgA (in four of four patients) and IgG (in three of four patients) antibodies were detected at the BMZ. Circulating IgA (in four of four patients) and IgG (in four of four patients) labeled the epidermal BMZ of normal human skin fractured at the lamina lucida and did not label the dermal BMZ. By immunoblot analyses, IgA (in three of three patients) and IgG (in one of three patients) circulating antibodies labeled the 97-kd linear IgA bullous dermatosis antigen. By direct immunoelectron microscopy, IgA and IgG antibodies were localized (in two of two patients) exclusively within the upper lamina lucida of the BMZ. Four cases of an immune-mediated blistering skin disease typical for linear IgA bullous dermatosis demonstrated both IgA and IgG anti-BMZ autoantibodies against the linear IgA bullous dermatosis antigen within the upper lamina lucida. We conclude that linear IgA bullous dermatosis should include a subgroup of patients with both IgA and IgG anti-BMZ autoantibodies.

Studies of Patients with Anti‐Epiligrin Cicatricial Pemphigoid

We have recently identified patients with a form of cicatricial pemphigoid who have IgG anti-basement membrane autoantibodies directed against epiligrin, a laminin isoform closely related if not identical to laminin 5. These patients' autoantibodies bind the lower lamina lucida of human epidermal basement membrane and immunoprecipitate this laminin isoform from extracts and media of biosynthetically radiolabeled human keratinocytes. Immunoblot studies show that these patients' autoantibodies specifically bind the alpha subunit of this laminin (i.e., laminin subunit alpha 3). We have found no evidence of these autoantibodies in normal volunteers or patients with other bullous skin diseases (including those with other forms of CP). These studies have identified a group of patients with an acquired, autoimmune, subepidermal bullous disorder who have disease-specific autoantibodies directed against the alpha subunit of epiligrin/laminin 5. These findings correlate with prior reports showing that a monoclonal antibody directed against this laminin subunit induces detachment of keratinocytes from extracellular matrix in vitro as well as epidermis from human skin in situ. Together, these findings suggest that this laminin mediates attachment of basal keratinocytes to epidermal basement membrane and that autoantibodies directed against it may be pathogenic. Moreover, recent studies showing that subunits of this laminin isoform are mutated in some patients with Herlitz's junctional epidermolysis bullosa indicate that acquired or inherited abnormalities in this adhesion ligand are associated with skin diseases characterized by separation of epidermis from epidermal BM.

Anti-Basement Membrane Autoantibodies in Patients with Anti-Epiligrin Cicatricial Pemphigoid Bind the α Subunit of Laminin 5

Recent studies have identified a group of cicatricial pemphigoid patients who have IgG anti-basement membrane autoantibodies that recognize epiligrin, a set of disulfide-linked polypeptides closely related if not identical to laminin 5 (formerly called kalinin, nicein, or BM600). To further understand the pathophysiology of blister formation in these patients, we have sought to identify the specific polypeptide(s) targeted by their autoantibodies. Comparative studies show that sera from these patients (nine of nine), P1E1 monoclonal anti-epiligrin antibody, and polyclonal as well as monoclonal anti-laminin 5 antibodies immunoprecipitate the same set of disulfide-linked polypeptides from media of biosynthetically radiolabeled human keratinocytes. Moreover, sera from eight of nine patients with anti-epiligrin cicatricial pemphigoid immunoblot the alpha subunit of laminin 5 but show no reactivity to its beta or gamma subunits. In addition, circulating IgG from a representative patient was affinity-purified against the alpha subunit of laminin 5 and shown to bind the dermal side of 1 M NaC1 split skin in the same manner as autoantibodies from all patients with anti-epiligrin cicatricial pemphigoid. Sera from patients with bullous pemphigoid (n = 5), other forms of cicatricial pemphigoid (n = 5), epidermolysis bullosa acquisita (n = 4), or bullous systemic lupus erythematosus (n = 1) show no reactivity against any subunit of this laminin isoform in immunoprecipitation or immunoblot experiments. These findings correlate with prior reports showing that a monoclonal antibody directed against the alpha subunit of laminin 5 (i.e., laminin subunit alpha 3) induces detachment of human keratinocytes from extracellular matrix in vitro as well as epidermis from human skin in situ. Together, these studies suggest that laminin subunit alpha 3 mediates attachment of basal keratinocytes to epidermal basement membrane and that autoantibodies directed against it may be pathogenic.

Antiepiligrin cicatricial pemphigoid. A subepithelial bullous disorder

<h3>Background:</h3> Epiligrin is a glycoprotein complex deposited in extracellular matrix by cultured human keratinocytes that serves as the major integrin ligand of these cells. In human skin, epiligrin is found at the interface of the lamina lucida and lamina densa in epidermal basement membrane where it is believed to be associated with anchoring filaments and plays an important role in keratinocyte adhesion. <h3>Methods and Results:</h3> We have identified six patients with a subepithelial bullous disorder of mucous membranes and skin who have IgG anti-basement membrane autoantibodies that immunoprecipitate epiligrin from human keratinocyte extracts and culture media. These patients' IgG autoantibodies also bind epiligrin in human keratinocyte extracellular matrix and epidermal basement membrane as determined by immunofluorescence and immunoelectron microscopy. Studies of 10 patients who are clinically indistinguishable from subjects with antiepiligrin autoantibodies (ie, cicatricial pemphigoid pa- tients) found that while seven had anti-basement membrane autoantibodies, the latter are directed exclusively against a region of epidermal basement membrane that does not contain epiligrin, are present in low titer (ie, ≤1:10), do not react with keratinocyte extracellular matrix, and do not bind epiligrin (or any other specific antigen) in immunoprecipitation studies of human keratinocyte extracts or media. Antiepiligrin autoantibodies were also not detected in studies of 36 additional patients with bullous diseases or six normal volunteers. <h3>Conclusions:</h3> Cicatricial pemphigoid is a disease phenotype in which patients' autoantibodies may target different constituents of epidermal basement membrane. Antiepiligrin autoantibodies are a specific immunologic marker for a group of patients with a disease entity that we propose to designate antiepiligrin cicatricial pemphigoid. (Arch Dermatol. 1994;130:1521-1529)

Antiepiligrin Cicatricial Pemphigoid

Epiligrin is a glycoprotein complex deposited in extracellular matrix by cultured human keratinocytes that serves as the major integrin ligand of these cells. In human skin, epiligrin is found at the interface of the lamina lucida and lamina densa in epidermal basement membrane where it is believed to be associated with anchoring filaments and plays an important role in keratinocyte adhesion. We have identified six patients with a subepithelial bullous disorder of mucous membranes and skin who have IgG anti-basement membrane autoantibodies that immunoprecipitate epiligrin from human keratinocyte extracts and culture media. These patients' IgG autoantibodies also bind epiligrin in human keratinocyte extracellular matrix and epidermal basement membrane as determined by immunofluorescence and immunoelectron microscopy. Studies of 10 patients who are clinically indistinguishable from subjects with anti-epiligrin autoantibodies (ie, cicatricial pemphigoid patients) found that while seven had anti-basement membrane autoantibodies, the latter are directed exclusively against a region of epidermal basement membrane that does not contain epiligrin, are present in low titer (ie, < or = 1:10), do not react with keratinocyte extracellular matrix, and do not bind epiligrin (or any other specific antigen) in immunoprecipitation studies of human keratinocyte extracts or media. Antiepiligrin autoantibodies were also not detected in studies of 36 additional patients with bullous diseases or six normal volunteers. Cicatricial pemphigoid is a disease phenotype in which patients' autoantibodies may target different constituents of epidermal basement membrane. Antiepiligrin autoantibodies are a specific immunologic marker for a group of patients with a disease entity that we propose to designate antiepiligrin cicatricial pemphigoid.

Epiligrin, the major human keratinocyte integrin ligand, is a target in both an acquired autoimmune and an inherited subepidermal blistering skin disease.

Epiligrin, the major component of human keratinocyte extracellular matrix, serves as the preferred integrin ligand for alpha 3 beta 1 in plasma membranes and focal adhesions, and colocalizes with alpha 6 beta 4 in hemidesmosomes. In human skin, epiligrin is found in the lamina lucida subregion of epidermal basement membrane, where it is thought to be associated with anchoring filaments. We have identified three patients with an acquired mucosal predominant subepidermal blistering disease who have IgG anti-basement membrane autoantibodies that bind the lamina lucida/lamina densa interface of epidermal basement membrane, stain cultured human keratinocyte extracellular matrix, and immunoprecipitate disulfide linked polypeptides of 170, 145, 125, and 95 kD in human keratinocyte culture media in a pattern identical to that of P1E1, a murine monoclonal antiepiligrin antibody. Comparative immunoprecipitation studies of patient sera, P1E1, and GB3 monoclonal antibody show that epiligrin is identical to the antigen (i.e., BM600 or GB3 antigen) previously reported to be absent from the skin of patients with lethal junctional epidermolysis bullosa, an inherited subepidermal blistering disease. Moreover, skin from a fetus with this disease shows no evidence of reactivity to patient antiepiligrin autoantibodies or P1E1. These studies show that antiepiligrin autoantibodies are a specific marker for a novel autoimmune blistering disease and that the epidermal basement membrane antigen absent in patients with lethal junctional epidermolysis bullosa is epiligrin.