Meeting the diagnostic challenge in canine and feline allergic skin disease.

Abstract

In the second edition of the textbook Allergic Skin Diseases of Dogs and Cats,1 the section on atopic disease begins as follows: ‘Atopy is a genetically determined predisposition to spontaneously develop Type I hypersensitivities to aeroallergens, which are normally innocuous substances’. Accordingly, it would be tempting to believe that atopy is a disease where pathophysiological elements are easily recognized and establishment of a diagnosis requires a straightforward procedure, leading to a beneficial treatment. Unfortunately, this is not so. In the same book, 140 pages are required to summarize and discuss the current knowledge and yet, during our confrontation with a potentially atopic patient in the clinic, we still know too little. Among dog owners as well as nondog owners, however, it is very popular to talk about allergy which, by the way, all too often is erroneously used as a synonym for atopy. If a patient has a noninfectious, undiagnosed pruritic condition, it is tempting to claim that the patient is allergic to something. This dilemma, combined with the apparent increase in the number of atopic dogs and cats seen in most veterinary clinics, most certainly triggers an increased demand for reliable, easily accessible, cheap, diagnostic tools. Allergens, IgE antibodies and mast cells have long been recognized as the major ingredients involved in atopy. Much effort has therefore been made to improve our understanding of these elements. Although it is seemingly too simplistic to maintain this concept unaltered, it is still important today that all three elements should be precisely characterized, not only to improve our diagnostic capability, but equally to ensure that continuous progress takes place in our search for a better understanding of atopy. A selected update of our understanding was provided at the HESKA/CMG Workshop on ‘Perspectives of Allergy Diagnosis in Companion Animals’ that was held as an ESVD/ECVD precongress activity in Pisa last year. Quantification of allergen-specific IgE antibodies was discussed, based on three different approaches. Use of polyclonal anti-IgE antibodies has been criticised on the basis that they are contaminated with irrelevant non-IgE(IgG?) antibody activity. However, in the study presented by Halliwell et al., data suggest, in a rather convincing way, that studies using highly purified polyclonal antibodies can lead to very interesting and important results. Thus, the highly relevant issue of heterogeneity of either IgE or of high-affinity mast cell receptors was raised. The basic concept of monoclonal antibodies being a crucial aspect in the search for reliable reagents for monitoring allergen-specific IgE antibodies was the focus of presentations by Hämmerling and de Weck, by Dérer et al. and by Zunic. Thus, a newly developed test system providing reliable semiquantitative analyses of allergen-specific canine IgE antibodies was critically discussed. Wassom and Grieve described a more recent development using alpha chains of the high-affinity mast cell IgE receptors to detect allergen-reactive IgE in the serum. Owing to their inability to bind antibodies other than IgE, this new achievement seems more than promising. IgE binds to high-affinity mast cell receptors and, thus, allergen-reactive IgE antibodies in serum can only provide a part of the relevant information for evaluation of an atopic patient. It is therefore of no less interest to follow the progress made in the studies of ‘IgE-loaded’ mast cell degranulation upon exposure to relevant allergens. The studies presented by Sainte-Laudy and by Prost strongly indicate that such a technique will be a valuable asset in much experimental work today and that it might, perhaps, become a valuable diagnostic tool in veterinary dermatology in the future. Finally, two papers not presented at the workshop have been included in this issue of Veterinary Dermatology. First, a review of mast cell biology by Hill and Martin. This pearl among reviews most certainly deserves to be read by everyone who has the slightest interest in atopy, including the disease in pet animals. The second article, by Mueller and Tsohalis, indicates that the technique, described at the HESKA/CMG Workshop, is seemingly unreliable in the diagnosis of adverse food reactions. This apparent controversy simply demonstrates that without reliable diagnostic tools veterinary dermatologists cannot effectively discriminate between an atopic patient and an atopic-like nonatopic patient. If all of the readers of this issue will retain a critical investigative approach, as demonstrated by Mueller and Tsohalis, the problem of diagnosing atopy and atopy-like conditions will eventually be solved and the gate for rational and curative therapies will open.