No abstract

The molecular and immunologic mechanisms associated with successful allergen-specific immunotherapy (ASIT) have not been completely elucidated. The aim of this study was to characterize the changes in Dermatophagoides farinae-specific IgG in atopic dogs undergoing ASIT using aqueous vaccines. Fifteen atopic dogs with a positive skin test reaction to D. farinae were treated with aqueous vaccines for a minimum of 2 months following a standard protocol. Serum samples were collected before and during therapy and used to probe Western blots containing separated proteins of D. farinae. IgG responses were detected using a polyclonal goat anticanine IgG antibody and a chromogenic substrate 3,3'-diaminobenzidine. The blots were analysed using a semiquantitative digital image analysis system that evaluated the number and molecular weight of bands, as well as their intensity, which was related to IgG concentration. Prior to ASIT, all dogs showed allergen-specific IgG responses to various antigens of D. farinae. During ASIT, there was a significant increase in the total quantity of D. farinae-specific IgG antibodies to various antigens from the mite (P = 0.015). Significant increases were observed for a 98-kDa band (P = 0.015), likely to be Der f 15; bands with molecular weights between 50 and 70kDa (P=0.012); and bands between 30 and 45 kDa (P = 0.035). These findings provide support for the hypothesis that ASIT induces IgG blocking antibodies to allergens known to be relevant in canine atopic dermatitis.

A semiquantitative chemiluminescent Western blot analysis system was developed and validated to evaluate antigen-specific IgG subclass responses to electrophoretically separated proteins of Dermatophagoides farinae in healthy and atopic dogs. Both groups mounted similar D. farinae-specific IgG1 and IgG4 responses to multiple antigens, but IgG2 and IgG3 responses were difficult to detect. The most commonly recognized bands in both groups were 18 and 98 kDa antigens for IgG1 and 18, 45, 66, 98, 130 and 180 kDa for IgG4. The number of bands recognized per dog did not differ significantly, but significantly more atopic dogs had an IgG1 response to a 180 kDa protein. The overall D. farinae-specific IgG1 and IgG4 responses were slightly higher, but not significantly different, in the healthy group. The results suggest that some antigens produced by D. farinae can induce different subclass responses. However, as most of these responses are seen in both healthy and atopic dogs, they are likely to merely represent recognition of foreign proteins presented to the immune system, rather than involvement in the pathogenesis of atopic dermatitis. The role of the 180 kDa antigen warrants further study.

Mixed infestations of Demodex canis and a short‐tailed demodectic mite were reported from several countries since late the 1980s. Differentiations based on measurement of the length of this short demodectic mite have been inconclusive until now. Over 500 adult demodectic mites were collected by tape strip and skin scrapings from a 4‐year‐old intact male Shih Tzu dog with severe juvenile‐onset generalized demodicosis. The dog had a mixed infestation of D. canis and the short‐tailed demodectic mite. Two studies were performed on the mites. In the first study, 200 mites were divided into two groups based on different morphology. Group 1: mites short body, rounded end of abdomen, one to three fold lines bilaterally on the abdomen. These criteria were used by the investigators to define the ‘short‐tailed’ demodectic mite. Group 2: mites with a slender and tapering free body end and no bilateral abdominal fold lines. One hundred mites were counted in each group. In the second study, 298 mites’ measurements were made independent of body shape. Total body length, width and body ratio of gnathosoma plus podosoma (= prosoma) to opisthosoma were measured. The total body length and width did not easily differentiate the two mites. The body ratio plus morphological characteristics of the rounded end of the abdomen appear to be the easiest method to identify the short‐tailed demodectic mite in the clinic.  This study was supported by the Association of Veterinary Dermatology, Taipei.