Page 1007 - Veterinary Immunology, 10th Edition

The division of AD into intrinsic and extrinsic disease results from
VetBooks.ir the observation that there is no consistent correlation between IgE

levels and the severity of clinical AD in dogs, and not all AD cases
are associated with IgE antibodies to environmental antigens (Box

30.2). Serological assays that measure IgE antibodies to the
offending allergens rarely correlate with disease severity or the
levels of IgE in the skin. Blood IgE levels may drop to undetectable
levels, whereas levels in skin and skin reactivity remain high.

Intradermal testing of pruritic dogs shows that many are sensitive
to house dust mites, various pollens (trees, weeds, grasses), and
epidermal allergens, as well as some seasonal allergens (Fig. 30.9).
However, skin testing of clinically normal dogs also elicits positive

reactions to these same antigens. For example, 50% to 90% of
clinically normal dogs react to house dust allergens. Allergen-
specific IgE may also be detected in dogs that have no clinical signs
of AD; however, IgE levels cannot discriminate between normal

dogs, dogs with intestinal parasites, or dogs with AD. Additionally,
about a quarter of canine cases are unreactive to intradermal
antigens and lack any allergen-specific IgE.

Box 30.2

Nomenclature

IgE mediates immediate hypersensitivity reactions, so-called
because they develop within seconds or minutes after exposure to
antigen. This type of hypersensitivity reaction is also commonly

called an allergy. Antigens that stimulate allergies may be called
allergens. If an immediate hypersensitivity reaction is systemic and
life threatening, it is called allergic anaphylaxis or anaphylactic

shock. Sometimes an animal may have a reaction that is similar to
allergic anaphylaxis but is not immunologically mediated. This
type of reaction is described as anaphylactoid.

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