Hyposensitization of Allergic Individuals: Let’s Stop this Itching!

Hyposensitization of Allergic Individuals:
Let’s Stop this Itching!

By Dr. Ed Mapes
Stonebridge Animal Hospital

This is the final installment of a series of articles that discussed allergic dermatitis in our pets. We have touched on the mechanism of the allergic response, possible causes, and medications used to counteract the symptoms. This article describes the ultimate treatment we can offer to allergic animals.
Hyposensitization, also known as immunotherapy, is the process by which an allergic animal’s immune system is re-trained so that it stops reacting to offending allergens. This results in a cessation of the immune response, with alleviation of allergy symptoms.
After blood tests identify the substances to which an animal is allergic, a serum that contains miniscule amounts of those allergens is formulated. We begin the process of hyposensitization by administering injections of the serum at specific intervals. The dosages are gradually increased until the immune system is re-programmed to stop producing reactive antibodies against those substances.
It is thought that the injection process diminishes synthesis of the antibody produced during allergic reactions (called IgE), while a different type of antibody is produced instead. Figure 1 illustrates how this “blocking antibody”, an allergen-specific IgG, neutralizes the allergen instead of IgE, and does so without initiating the allergic cascade of events. Since the allergen never attaches to IgE, the substances responsible for an allergic reaction are not released and allergy symptoms don’t appear. The animal becomes capable of being exposed to the offending substances without incurring the allergy that it formerly suffered.

Figure 1

Figure 1

Figure 1 the top illustration demonstrates an IgE antibody sensitized to this antigen attached to a mast cell. When the allergen attaches to the IgE, the allergic reaction is stimulated. A different antibody has been produced because of the hyposensitization process in the lower diagram. This IgG antibody is seen connected to the allergen, thus blocking access to the IgE and preventing the allergy.

Immunotherapy involves injections of the allergen extract serum with small syringes and needles similar to those used when giving insulin. Injections are normally very well tolerated by the patient when placed under the loose skin atop the shoulder area – the least painful site to give injections. We sometimes give antihistamines prior to the injections to reduce the likelihood of local discomfort and other side-effects.

The dosage is gradually increased until a “maintenance” dose is reached, and the animal’s symptoms are controlled. This usually means four to six months of weekly injections. Once the maintenance dose is reached, the injections are administered less often (every two to four weeks), on a regular basis. Generally, the longer the treatment and the higher the dose, the greater the therapeutic benefit. Extended protection can last for 3–5 years or more. Therapy can be repeated if symptoms begin to return or if the animal develops allergies to new substances that had not previously caused symptoms.

While allergy testing is best done during the peak allergy season, or when symptoms are at their worst, hyposensitization is best begun when the allergy is less severe. We usually give other medications to control the itch when starting the allergy injections, since the response is not immediate – two to four months should be allotted for control in most cases.

Statistics show the process to be effective in controlling roughly 80% of allergy cases. The remaining 20% show varying degrees of improvement, sometimes requiring intermittent dosages of antihistamines or corticosteroid therapy to control symptoms. In those patients, times of high allergen exposure can cause a return of some itch symptoms.

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