Novel feline autoimmune blistering disease resembling bullous pemphigoid in humans: IgG autoantibodies target the NC16A ectodomain of type XVII collagen (BP180/BPAG2)

Spontaneous autoimmune subepidermal blistering diseases in animals: a comprehensive review

Autoimmune subepidermal blistering diseases (AISBDs) are rare skin disorders of animals that were first identified in dogs but several AISBDs are now recognised in other companion animal species. Most AISBDs in animals are homologues of the human diseases and are thought to share similar pathomechanisms of epidermal and/or mucosal blister formation caused by autoantibodies targeting structural proteins of the basement membrane zone (BMZ). Disruption of their structural function by the autoantibodies and/or recruited inflammation leads to BMZ fragility, which presents clinically as vesicles, bullae and, later, deep erosions and ulcers. Canine AISBDs are the best characterised, particularly the more common variants such as mucous membrane pemphigoid (48%), epidermolysis bullosa acquisita (EBA) (26%), and bullous pemphigoid (10%). Exceedingly rare AISBDs in the dog are junctional EBA, mixed AISBD, type-1 bullous systemic lupus erythematosus, linear IgA dermatosis, and pemphigus gestationis. The diagnosis of a specific AISBD is made by combining the clinical features (breed, age, lesion distribution) with histological evidence of subepithelial clefting, but not all AISBDs can be differentiated in this manner and specialised immunological testing is required. This latter, unfortunately, is not readily available and, therefore, the specific AISBD diagnosis often remains unconfirmed. While this limits further understanding of these diseases, it does not prevent clinicians from treating their patients, as the treatment approaches are similar for the different AISBDs in dogs. This review primarily focuses on canine AISBDs, the species for which these diseases have been best characterised, and shorter descriptions of variants in other species are also provided.

Management of Severe Oral Inflammatory Conditions in Dogs and Cats

Severe oral inflammatory disease is not uncommon in the mouths of canine and feline patients. An approach to oral diagnosis is offered. This article discusses a brief review of important points in the oral diagnosis and management of main canine (canine chronic ulcerative stomatitis (CCUS), eosinophilic stomatitis, and Wegener's granulomatosis (WG)) and feline diseases (feline gingivostomatitis/caudal stomatitis, oral eosinophilic lesions, pyogenic granuloma, and autoimmune diseases with oral manifestations), and-whereby possible-information about the current understanding of disease pathogenesis and treatment is offered.

Bullous pemphigoid. Сlinic, Diagnosis and Treatment

The article describes modern views on the predisposing factors, features, immunological changes and link with the histocompatibility antigens HLA, the role of circulating autoantibodies, cytokines, chemokines, matrix metalloproteinases and BP180 (BPAg2) и BP230 (BPAg1), those role in the pathogenesis of the bullous pemphigoid and their correlation with the activity of pathological process in patients with bullous pemphigoid. Described experimental model of the disease in animals, modern medications and methods of treatment of this disease.

Molecular organization of the basement membrane zone

The dermal-epidermal basement membrane is a complex assembly of proteins that provide adhesion and regulate many important processes such as development, wound healing, and cancer progression. This contribution focuses on the structure and function of individual components of the basement membrane, how they assemble together, and how they participate in human tissues and diseases, with an emphasis on skin involvement. Understanding the composition and structure of the basement membrane provides insight into the pathophysiology of inherited blistering disorders, such as epidermolysis bullosa, and acquired bullous diseases, such as the pemphigoid group of autoimmune diseases and epidermolysis bullosa acquisita.

Role of dermal-epidermal basement membrane zone in skin, cancer, and developmental disorders

The dermal-epidermal basement membrane zone is an important epithelial and stromal interface, consisting of an intricately organized collection of intracellular, transmembrane, and extracellular matrix proteins. The basement membrane zone has several main functions including acting as a permeability barrier, forming an adhesive interface between epithelial cells and the underlying matrix, and controlling cellular organization and differentiation. This article identifies key molecular players of the dermal-epidermal membrane zone, and highlights recent research studies that have identified structural and functional roles of these components in the context of various blistering, neoplastic, and developmental syndromes.

Bullous pemphigoid: physiopathology, clinical features and management

There has been a considerable progress in the understanding of the physiopathology of BP during the past 2 decades. The insights into the humoral and cellular immune response against BP180 and BP230 have increased significantly. Nevertheless, the factors underlying the initiation of the disease leading to a disruption of self-tolerance remain unclear. Clinically, the disease shows protean presentations, and diagnostic delay is common. A practical, relevant, and unresolved question is how to identify patients suffering from BP at an early stage of the disease, when direct immunofluorescence microscopy findings still may be negative. The characterization of markers allowing the differentiation of BP from other pruritic eruptions occurring in the elderly population would be extremely helpful in daily practice. Finally, despite the knowledge that potent topical steroids are efficient in controlling the disease, management of BP sometimes remains difficult and requires systemic therapies. It is hoped that a better knowledge of the regulation of the autoimmune response in BP also will facilitate the design of novel immunomodulatory therapeutic approaches devoid of the severe side effects of current immunosuppressive treatments.

Gingivostomatitis

Gingivostomatitis (GS) with various patterns of disease may require antiviral therapy, steroids, laser fulguration, immunomodulation drugs, or nonsteroidal anti-inflammatory drugs. The use of cyclosporine as an immunomodulation drug has long-term benefits in reduction of the immunologic events that contribute to GS. Whole-mouth extraction or partial extraction (premolars and molars), with radiographic conformation that all root remnants have been removed, may be the most viable option in nonresponsive and or intractably painful stomatitis in noncompliant cats or dogs. Oral inflammation subsided after extraction without the need for further medication in approximately 70% of the cats from two studies with previous chronic unrelenting oral disease. The combination of immunomodulation with cyclosporine together with laser resection of proliferative tissue should be recommended if extraction of teeth is not desired. Removal of proliferative oral tissues by lasing (carbon dioxide laser) removes the tissue that maybe producing tissue antigens and the area where bacteria are sequestered. The use of anti-inflammatory medications is recommended in the management of GS. Therapeutic success is achieved when there is elimination of proliferative tissue and inflammation.

Molecular cloning of a cDNA encoding the porcine type XVII collagen noncollagenous 16 A domain and localization of the domain to the upper part of porcine skin basement membrane zone

Bullous pemphigoid is an autoimmune blistering human skin disease mediated by immunoglobulin (Ig)G autoantibodies targeting skin basement membrane component type XVII collagen, a transmembrane protein. Also designated BP180 and BPAG2, type XVII collagen is an extracellular matrix element essential for the connection between the epidermis and the underlying dermis. In addition to being a target antigen in the human disease bullous pemphigoid, type XVII collagen is also targeted by autoantibodies of canine, feline, equine and porcine patients suffering from a similar blistering skin disease. Previously, enzyme-linked immunosorbent assay and Western blot analyses have shown that autoantibodies from pigs affected with bullous pemphigoid recognize the human NC16A domain of type XVII collagen. To facilitate the development of porcine model of bullous pemphigoid, we isolated cDNA encoding the porcine type XVII collagen NC16A domain using a reverse transcription-polymerase chain reaction technique. The amino acids deduced from the NC16A cDNA showed 61% identity with the sequence of human NC16A. An antibody generated against a 20-amino acid peptide within the porcine NC16A localized the NC16A epitope to the upper part of porcine skin basement membrane zone. Our data provide further information of the porcine bullous pemphigoid target antigen and may help investigators for their further studies of this disease.

Intraocular extramedullary plasmacytoma in a cat

An 8-year-old, castrated male Domestic Short-haired cat was referred for evaluation of a possible intraocular neoplasm following previous ocular trauma. The eye was blind, and uveitis and an iridal mass were noted on examination. An enucleation was performed and the mandibular lymph node excised. Histopathologic examination revealed neoplastic proliferation of plasma cells in the iris and lymph node. No other evidence of disseminated disease was detected. This is the first case reported of an intraocular extramedullary plasmacytoma in the cat. The variation in clinical manifestations and potential association with multiple myeloma are not known at this time. Disseminated metastasis from a primary plasmacytoma of the uveal tract could also involve the bone marrow and be indistinguishable from multiple myeloma. Early enucleation, as in trauma-associated sarcomas, may be indicated to prevent metastasis. Periodic systemic evaluation for evidence of multiple myeloma should be performed.

Laminin-5 is targeted by autoantibodies in feline mucous membrane (cicatricial) pemphigoid

In human and canine patients with mucous membrane (cicatricial) pemphigoid (MMP), circulating autoantibodies have been shown to target multiple epidermal basement membrane antigenic epitopes. These autoantigens include collagen XVII in humans and dogs, as well as laminin-5, laminin-6 or integrin alpha-6/beta-4 in human beings. The purpose of this study was to determine if autoantibodies targeted laminin-5 in a cat exhibiting clinical and microscopic lesions resembling those of MMP in humans. In this patient, an indirect immunofluorescence (IF) assay revealed circulating IgG and IgA autoantibodies that bound to the basement membrane zone on the dermal side of salt-split gingiva (titer 1:1000 for IgG and 1:50 for IgA). Immunoblotting, performed with affinity-purified human laminin-5, demonstrated that the autoantibodies bound the alpha-3 chain of this heterotrimer. These observations identify laminin-5 as one of the antigens recognized by circulating autoantibodies in this feline homologue of MMP in humans and dogs.

Characterization of BALB/c mice B lymphocyte autoimmune responses to skin basement membrane component type XVII collagen, the target antigen of autoimmune skin disease bullous pemphigoid

Bullous pemphigoid is an autoimmune blistering skin disease characterized by IgG autoantibodies targeting the skin basement membrane component type XVII collagen (BPAg2). To gain understanding of the disease's induction phase, we subcutaneously immunized adult BALB/c mice with peptides of human and/or the murine-equivalent BPAg2 pathogenic NC16A domain. Female mice were injected with peptides (human, murine, or combined human and murine), or PBS control emulsified in CFA, on a four-week interval. At the fourth and subsequent immunizations, all peptide-immunized mice were given murine peptides. Two weeks after the sixth immunization, ELISA detected IgG circulating autoantibodies against self peptides in 92% (47/51) of mice immunized with murine peptides; whereas none of the preimmune sera or the sera from PBS control-immunized mice reacted to the self peptides. In four mice their autoantibodies labeled mouse skin basement membrane. Breaking B-cell tolerance to BPAg2 sets the first step in dissecting the disease's induction phase.

Hemizygosity for a glycine substitution in collagen XVII: unfolding and degradation of the ectodomain

Defects of collagen XVII, a keratinocyte adhesion protein, are associated with epidermal detachment in junctional epidermolysis bullosa. Although some missense mutations in the collagen XVII gene COL17A1 have been described, the molecular mechanisms leading to disease have remained elusive in these cases. Here we assessed the biologic consequences of a missense mutation by studying the folding and stability of wild-type and mutated recombinant collagen XVII domains. The mutation occurred in a junctional epidermolysis bullosa patient who was compound heterozygous for the novel glycine substitution mutation G633D and the novel nonsense mutation R145X. Collagen XVII mRNA was significantly reduced, indicating nonsense-mediated mRNA degradation and hemizygosity of the patient for the G633D substitution. As glycine residues within the collagen triple helices are important for stable conformation, the thermal stability of the wild-type and mutated eukaryotic recombinant Col15 domain of collagen XVII was assessed. The stability of the mutated fragment was clearly reduced. The midpoint of the helix-to-coil transition, Tm, was 5 degrees C lower than that of wild-type rCol15, indicating abnormal triple-helix folding and susceptibility to proteolysis. Consistently, immunoassays demonstrated reduced amounts of the full-length collagen XVII and absence of the soluble ectodomain in keratinocyte cultures, and lack of the ectodomain from the junctional epidermolysis bullosa skin. These observations show that the glycine substitution G633D in collagen XVII causes abnormal folding and susceptibility to degradation, and thus perturbs the physiologic adhesive functions of collagen XVII in the skin.

Autoantibodies against the processed ectodomain of collagen XVII (BPAG2, BP180) define a canine homologue of linear IgA disease of humans

Linear IgA disease (LAD) is an acquired autoimmune subepidermal blistering dermatosis that affects human children and adults. In contrast to bullous pemphigoid, in which autoantibodies recognize transmembrane type XVII collagen (BP180, BPAG2), LAD is associated with skin-fixed and circulating IgA autoantibodies that target LAD-1, the processed extracellular form of type XVII collagen. An immunologic homologue of LAD in humans was identified in two dogs according to the following criteria: 1) erosive, ulcerative, and crusted lesions seen on the face, in the oral cavity, and on the extremities, 2) dermoepidermal clefting present in the basement membrane lamina lucida without inflammation or with mild neutrophilic infiltration, 3) basement membrane-fixed IgG and/or IgA antibodies, and 4) circulating IgA and IgG autoantibodies that target the 120-kd soluble protein LAD-1. The present study establishes unequivocally the existence of a naturally occurring canine model of LAD of humans.

Equine bullous pemphigoid IgG autoantibodies target linear epitopes in the NC16A ectodomain of collagen XVII (BP180, BPAG2)

Bullous pemphigoid (BP) is an autoimmune subepithelial blistering dermatosis of humans, dogs, cats and pigs. It is characterized by skin-fixed and circulating IgG autoantibodies that target one or both BP antigens. An immunological homologue of BP in humans was diagnosed in two horses with cutaneous and mucosal ulcerations as well as microscopic subepithelial vesiculation. Immunological investigations revealed similar findings for both the horses. Direct immunofluorescence demonstrated the presence of IgG deposited linearly at the dermoepidermal junction in mucosal and skin biopsy specimens. Indirect immunofluorescence testing confirmed the existence of circulating basement membrane-specific IgG autoantibodies. Using intact and salt-split epithelial substrates, serum IgG were shown to target antigens situated not only at the basal, but also at the lateral and apical aspects of stratum basale keratinocytes. Immunoblotting and ELISA corroborated that the IgG from affected horses, but not those from normal controls, exhibited high immunoreactivity against the NC16A extracellular domain of type XVII collagen (BPAG2, BP180). Equine BP could be proposed, therefore, as another spontaneous model of this most common basement membrane autoimmune dermatosis of humans.