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. OBJECTIVES: The objectives of this study were to determine whether repeated applications of Dermatophagoides farinae slurry to intact skin of Maltese-Beagle atopic (MAB) dogs would result in the development of clinical signs or lesions resembling spontaneous canine AD, to determine whether repeated slurry applications would induce elevations in mite-specific IgE and/or IgG, and to determine whether mite antigens could be demonstrated within the dermis of application sites. METHODS: Dogs received weekly slurry applications to the axilla and groin, and were patch tested at 120 days, or were patch tested at days 1, 60 and 120, but did not receive further slurry applications. Skin biopsies and serum samples were obtained on days 1, 60 and 120. RESULTS: Pruritic dermatitis was seen in all dogs by day 60. D. farinae-specific IgE was elevated by day 60. Histologic examination of early application sites revealed mild, mononuclear perivascular dermatitis. Later application sites were characterized by a dense inflammatory infiltrate and oedema in both the dermis and the epidermis. Immunofluorescent staining confirmed the presence of D. farinae antigens in the dermis. CONCLUSIONS: This study demonstrated that epicutaneous application of HDM slurry to MAB dogs results in elevations of HDM-specific IgE, localized and generalized pruritic dermatitis resembling spontaneous canine AD, and histologic changes typical of IgE-driven inflammation. We feel that these results suggest that epicutaneous exposure to allergen may play an important role during both the sensitization and the perpetuation of AD, and provide support for the use of a canine model in the investigation of the pathogenesis of AD.

Allergenic cross-reactivities in flea-reactive canine serum samples.

OBJECTIVES: To determine whether flea extract could be determined (via ELISA) to share allergenic epitopes with other insects, and to determine whether sera with different reactivities to insect extracts have different cross-reactivity patterns. SAMPLE POPULATION: 69 canine serum samples that were selected from samples submitted for routing ELISA allergy testing and had previously been found to have high reactivities to flea. PROCEDURE: Each serum sample was assessed by means of a direct ELISA for IgE binding to 11 common insects. Samples that were reactive primarily to flea extract alone were designated pool 1, samples that were reactive to small numbers of insects were designated pool 2, and samples that were reactive to all or almost all insects were designated pool 3. Samples that did not have any apparent patterns of cross-reactivity were not included in the rest of the study. Inhibition ELISA techniques were used with the 3 serum pools to determine whether multiple insect extracts inhibited reactivity on flea-coated ELISA plates. Those extracts were used to coat ELISA plates, and reciprocal inhibition studies were then performed. RESULTS: Black fly, black ant, and cockroach extracts were capable of > 50% inhibition of flea solid-phase IgE binding with all 3 serum pools. In the ELISA inhibition studies, flea extract was able to inhibit IgE binding to each extract with all pools, confirming reciprocal inhibition. CONCLUSIONS: Inhibition of IgE binding to solid-phase flea antigen by black ant, black fly, and cockroach extracts suggested sharing of allergenic epitopes among these species. Reciprocal inhibition studies further confirmed these findings. These results indicated in vitro cross-reactivity between flea, black ant, black fly, and cockroach extracts. These results need to be further investigated in vivo. CLINICAL RELEVANCE: It is possible that dogs may become sensitized to fleas via exposure to other insects, and flea allergenic dogs may have signs of pruritus, in the absence of fleas, if exposed to cross-reactive insects.

Megakaryoblastic leukemia in a dog.

A 7-year-old spayed Louisiana Catahoula Leopard dog was examined to determine the cause of shifting forelimb lameness, anorexia, and lethargy. The dog was pyrectic and had splenomegaly, thrombocytopenia, and nonregenerative anemia. Examination of a bone marrow aspirate revealed hypocellularity with normal maturation of erythroid and granulocytic cell lines; however, approximately half of the cells were large undifferentiated blast cells. These cells were identified as megakaryoblasts, using immunohistochemical techniques to detect reactivity for Factor VIII-related antigen and platelet glycoprotein IIIa. Necropsy revealed diffuse neoplastic involvement of the spleen, liver, lungs, bone marrow, and lymph nodes. Cellular infiltrate was characterized by a mixture of megakaryoblasts and typical megakaryocytes. Megakaryoblastic leukemia (M7) is the designation proposed by the Animal Leukemia Study Group for myeloproliferative neoplasms of megakaryocytic lineage.