SELECTING ALLERGENS FOR IMMUNOTHERAPY
The allergens included in the immunotherapy solution are selected based on several principles, and companies may differ on
the number of allergens they will include in a treatment solution. In general, the maximum number will be included as long
as the dog reacts to that many allergens and is potentially exposed to them.
Dermatophagoides species allergen is always included if a dog has any allergic reaction to this mite, even if a mild one (pruritus level 2+).
After that, the stronger reactions (3 or higher) are initially selected, and then milder (2+) reactions are selected to reach
the maximum number allowed in the treatment mix.
Mold allergens are not included unless a dog has strong reactions to them. Pollen allergens are included and are partially
selected based on seasonal exacerbations. For example, dogs with clinical signs that are worse in the early spring will be
treated for even mild reactions (2+) to trees that are known to pollinate in that season. The allergen company should be able
to inform you about plant pollination timing for allergens of interest.
Insect allergens may be present year-round, although they are usually worse in the summer. With insects, it is important to
ask the client about possible exposure. Patients may exhibit cross-reactions with cockroach allergen and multiple insect allergens,
and dogs known to be exposed (either indoors or outdoors) to many insects such as beetles or silverfish may have cockroach
allergen included in their immunotherapy solution. Although clients may think their dogs are not exposed to ants and flies,
these allergens are included if allergic dogs spend a lot of time outside. Flea allergen is only included when a dog appears
flea allergic even when good flea control is used, when fleas are not found although outdoor exposure is likely, or when a
dog's exposure to fleas can't be controlled.
The selected allergens should be those the dog is likely exposed to, though many allergens, especially pollens, are airborne
and may travel many miles and persist indoors longer than they are present outdoors. When numerous allergens must be left
out, selected allergens from each group (e.g. weeds, trees, grasses, epithelials, insects) can be used. However, in regions in which Bermuda grass grows, Bermuda grass
allergens are always included because this type of grass does not stimulate cross-reactions well with other grasses. Some
of the weaker-reacting grass allergens may be left out since they more likely share cross-reacting allergens with other grasses.
Other components, including pollens, are picked based on which types are known to be more allergenic (cause reactions in a
higher percentage of dogs). This information also differs by region and can usually be acquired from the company making the
allergen solutions.
VIALS AND PROTOCOLS
How does allergen-specific immunotherapy work?
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Allergen companies will initially supply allergens in two or three vials. Each vial will contain the allergens mixed in a
liquid diluent, often referred to as the allergen solution. And each vial of allergen solution will be a particular concentration. The most dilute, lowest concentration allergen solution
vials are used initially, and the treatment follows a protocol to gradually build to the highest concentration of allergen
solution.
The concentration is usually defined as protein nitrogen units (PNU) or weight to volume. In the protocols I use, the concentration
of the initial allergen solution (vial 1) is generally 1,000 to 2,000 PNU/ml. The vial that becomes the maintenance vial typically
has a total allergen solution concentration of 10,000 to 20,000 PNU/ml, with the largest concentration per allergen usually
being 2,000 PNU/ml and infrequently up to 6,000 PNU/ml.
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