Late-phase reactions to intradermal testing with Dermatophagoides farinae in healthy dogs and dogs with house dust mite-induced atopic dermatitis

Patch testing of experimentally sensitized beagle dogs: development of a model for skin lesions of atopic dermatitis

In humans with atopic dermatitis (AD), the epicutaneous application of allergens (atopy patch tests or APT) to which the patients are sensitized often results in the development of inflammation resembling that of spontaneous skin lesions. Dogs are affected with a natural homologue of human AD, but information on the induction of positive patch testing reactions is limited. The objectives of this pilot study were to determine the nature and cellular dynamics of inflammation occurring after APT in dogs hypersensitive to house dust mite and flea allergens. Laboratory Beagles were sensitized experimentally to Dermatophagoides farinae house dust mites (two dogs), Ctenocephalides felis flea saliva (one dog) or both (two dogs). Two other dogs served as nonsensitized controls. Both allergens and saline were applied epicutaneously. Macroscopic evaluations and skin biopsies were performed at 4, 24, 48 and 96 h after starting allergenic challenge. Biopsies were evaluated histologically and immunohistochemically with a panel of monoclonal antibodies specific for canine leucocyte antigens. Positive macroscopic reactions consisted of erythema, oedema and induration, and they occurred between 24 and 96 h after allergen application. Macroscopic and microscopic APT reactions developed only whenever serum IgE was present against tested allergens. Microscopically, positive APT was associated with epidermal hyperplasia, Langerhans' cell hyperplasia, and eosinophil and lymphocyte epidermotropism. Dermal inflammation was mixed and arranged in a superficial perivascular to interstitial pattern. Numerous IgE+-CD1+ dendritic cells and gamma-delta T-lymphocytes were observed. Macroscopically and microscopically, APT reactions in these experimentally sensitized animals resembled those seen in lesional biopsy specimens of dogs and humans with spontaneous AD. Therefore, APT in hypersensitive dogs provides a relevant experimental model to investigate the pathogenesis and treatment of both canine and human AD skin lesions.

A randomized controlled trial of misoprostol monotherapy for canine atopic dermatitis: effects on dermal cellularity and cutaneous tumour necrosis factor-alpha

In this blinded randomized placebo-controlled trial, 20 dogs with atopic dermatitis (AD) were given placebo (8 dogs) or misoprostol (12 dogs) at 5 micro g kg-1, orally, three times daily for 3 weeks. Administration of the active drug, but not of placebo, led to a significant decrease in lesional and pruritus scores. The median reduction from baseline of both scores was approximately 30%. Misoprostol therapy did not lead to decreases of dermal cell counts or skin tumour necrosis factor (TNF)alpha mRNA copy numbers that were significantly different from those of placebo. Skin TNFalpha protein production, assessed using indirect immunofluorescence, decreased or remained unchanged in dogs receiving misoprostol. In contrast, post treatment TNFalpha fluorescence scores were higher in all but two dogs given placebo. The changes from baseline of TNFalpha fluorescence scores did not correlate significantly with those of lesional or pruritus indices. These observations confirm the modest efficacy of misoprostol for treatment of canine AD and suggest that its mild anti-allergic effects are not associated with either inhibition of inflammatory cell emigration or TNFalpha production.