Stanley M. Dunston

Electron Microscopic Observations of Stratum Corneum Intercellular Lipids in Normal and Atopic Dogs

The barrier function of mammalian skin is maintained by intercellular stratum corneum lipids. In human patients with atopic dermatitis, an abnormal lipid barrier results in dry skin and increased transepidermal water loss. At this time, it is not known if a defective lipid barrier is present in atopic dogs. Normal and atopic canine skin were postfixed in ruthenium tetroxide and studied using transmission electron microscopy to determine structural differences within stratum corneum lipids. Intercellular lipid lamellae were graded on a semiquantitative scale. The deposition of stratum corneum lipid lamellae in atopic canine skin appeared markedly heterogeneous compared with that seen in normal canine skin. When present, the lamellae often exhibited an abnormal structure. The continuity and thickness of the intercellular lipid lamellae were significantly less in nonlesional atopic than in normal canine skin. These preliminary observations suggest that the epidermal lipid barrier is defective in atopic canine skin. Additional studies are needed to further characterize the biochemical defect and to possibly correct it with nutritional and/or pharmacologic intervention.

Epicutaneous sensitization with Dermatophagoides farinae induces generalized allergic dermatitis and elevated mite-specific immunoglobulin E levels in a canine model of atopic dermatitis

Background Atopic dermatitis (AD) is a cutaneous hypersensitivity associated with elevated levels of antigen‐specific IgE, commonly to house dust mites (HDMs). It remains controversial as to whether sensitization and clinical disease are induced by cutaneous exposure to HDM.

Stratum corneum removal facilitates experimental sensitization to mite allergens in atopic dogs

In humans with atopic dermatitis and in mouse models of IgE-mediated allergic diseases, evidence is mounting that the stratum corneum (SC) provides an important barrier against environmental allergens. At this time, it is not known whether the SC has a similar role in dogs, especially in those with atopic dermatitis. The objectives of this pilot study were to determine whether SC removal led to earlier and stronger sensitization of atopic dogs to Dermatophagoides farinae (Df) house dust mites. Five Maltese-beagle atopic (MBA) dogs were sensitized epicutaneously after the SC was removed with ten tape strips (TS group), while sensitization was done without tape strips in five other MBA dogs (nontape stripping; NTS group). During this 16 week study, sensitization was assessed with allergen-specific IgE serology, intradermal testing with Df allergens and determination of stimulation indices of blood mononuclear cells cultured with Df and stained for CD4 and the activation markers CD25 or CD30. Compared with dogs from the NTS group, those of the TS group exhibited earlier rises in Df-specific IgE serum levels, usually had higher allergen-specific IgE titres, showed higher intradermal test reactivity and had earlier increases and higher percentages of CD25- or CD30-positive activated allergen-specific peripheral CD4-positive T lymphocytes. These observations implicate a role of the SC as a barrier limiting sensitization to exogenous allergens in this experimental atopic dog model.

A natural canine homologue of alopecia areata in humans.

Background  Alopecia areata (AA) is suspected to be an autoimmune disease directed preferentially against hair follicles (HF) affecting both humans and various mammalian species. Recently, two rodent models of AA were described, namely the ageing C3H/HeJ mouse and the DEBR rat. Despite several case reports of canine AA in the literature, there has been no systematic assessment of the disease in these companion animals, and it is also not known whether dogs with AA could be useful as an outbred homologue of this disease in humans.

Parvovirus Infection of Keratinocytes as a Cause of Canine Erythema Multiforme

Erythema multiforme major was diagnosed in a dog with necrotizing parvoviral enteritis. Skin lesions consisted of ulceration of the footpads, pressure points, mouth, and vaginal mucosa; vesicles in the oral cavity; and erythematous patches on the abdomen and perivulvar skin. Microscopic examination of mucosal and haired skin specimens revealed lymphocyte-associated keratinocyte apoptosis at various levels of the epidermis. Basophilic cytoplasmic inclusions were seen in basal and suprabasal keratinocytes. Immunohistochemical staining, performed with canine parvovirus-2-specific monoclonal antibodies, confirmed the parvovirus nature of the inclusions in the nucleus and cytoplasm of oral and skin epithelial cells. This is the first case of canine erythema multiforme reported to be caused by a viral infection of keratinocytes. This case study indicates that the search for epitheliotropic viruses should be attempted in cases of erythema multiforme in which a drug cause cannot be identified.

Reduced Anchoring Fibril Formation and Collagen VII Immunoreactivity in Feline Dystrophic Epidermolysis Bullosa

Dystrophic epidermolysis bullosa was diagnosed in a cat with juvenile-onset epithelial sloughing of the oral mucosa, footpads, and haired skin. Dermoepidermal separation occurred in the absence of inflammation or cytolysis of basal epidermal cells. Collagen IV-specific immunostaining corroborated the fact that clefting took place below the epidermal basement membrane. Ultrastructural examination revealed that the probands anchoring fibrils exhibited a filamentous morphology and were decreased in number compared with those in a normal cat. Finally, the attenuated immunoreactivity for collagen VII in our patient led us to suspect that its encoding gene, COL7A1, could be mutated in this case of feline dystrophic epidermolysis bullosa.

Desmoglein-3 is a target autoantigen in spontaneous canine pemphigus vulgaris

Abstract: Pemphigus vulgaris (PV) is an autoimmune blistering skin disease of humans and companion animals. In human patients, PV is associated with the production of IgG autoantibodies specific for keratinocyte desmosomal glycoproteins of the cadherin family. The purpose of this study was to determine whether antikeratinocyte IgG autoantibodies were present in the skin and serum of dogs with PV, and also to identify the canine PV autoantigen(s) targeted by circulating autoantibodies. Eleven dogs were selected because of the microscopic demonstration of suprabasal epithelial acantholysis. Direct immunofluorescence revealed the presence of IgG autoantibodies bound to the membrane of keratinocytes in skin biopsy specimens of 8/9 dogs (89%). Using indirect immunofluorescence, serum‐circulating IgG autoantibodies were found in 10/11 (91%) and 5/11 (45%) dogs, using normal canine gingiva and cultured canine oral keratinocytes, respectively. By immunoblotting using cultured canine oral keratinocyte protein lysates, IgG autoantibodies from 7/9 (78%) tested dogs recognized a 130‐kDa antigen that comigrated with that identified by rabbit polyclonal antibodies raised against desmoglein‐3. This 130 kDa antigen was confirmed to represent the canine equivalent of human desmoglein‐3 by immunoprecipitation‐immunoblotting. The results of these studies provide evidence that the canine desmoglein‐3 homologue is a major autoantigen in dogs with PV. These observations further establish spontaneous canine PV as a natural model for research on pathogenesis, etiology and novel therapeutic approaches for this disease of humans.

Novel Feline Autoimmune Blistering Disease Resembling Bullous Pemphigoid in Humans: IgG Autoantibodies Target the NC16A Ectodomain of Type XVII Collagen (BP180/BPAG2)

In humans and dogs, bullous pemphigoid (BP) is an autoimmune blistering disease associated with the production of basement membrane autoantibodies that target the 180–kd type XVII collagen (BP180, BPAG2) and/or the 230-kd plakin epidermal isoform BPAGle (BP230). In two adult cats, an acquired dermatosis and stomatitis was diagnosed as BP subsequent to the fulfillment of the following criteria: 1) presence of cutaneous vesicles, erosions, and ulcers; 2) histologic demonstration of subepidermal vesiculation with inflammatory cells, including eosinophils; 3) in vivo deposition of IgG autoantibodies at the epidermal basement membrane zone; and 4) serum IgG autoantibodies targeting a 180-kd epidermal protein identified as type XVII collagen. In both cats, the antigenic epitopes targeted by IgG autoantibodies were shown to be situated in the NC16A ectodomain of type XVII collagen, a situation similar to that of humans and dogs with BP. Feline BP therefore can be considered a clinical, histopathologic, and immunologic homologue of BP in humans and dogs.

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.

Bullous systemic lupus erythematosus (type I) in a dog

In human patients with systemic lupus erythematosus, cutaneous subepidermal blistering can occur because of the production of antibodies specific for basement membrane antigens. This condition is referred to as bullous systemic lupus erythematosus (BSLE). A dog was diagnosed with BSLE because it because of the production of antibodies specific for basement membrane antigens. This condition is referred to as bullous systemic lupus erythematosus (BSLE). A dog was diagnosed with BSLE because it fulfilled the following criteria: (i) a diagnosis of systemic lupus erythematosus by standard methods; (ii) an acquired, vesicular, erosive and ulcerative eruption; (iii) microscopical subepidermal vesicles with neutrophil-predominant inflammation at the dermo-epidermal junction; (iv) deposition of IgG at the epidermal basement membrane zone; and (v) circulating IgG autoantibodies against type VIl collagen. Anti-collagen Vil type l-BSLE therefore needs to be considered as a possible differential diagnosis for canine autoimmune subepidermal blistering diseases.