Allergen immunotherapy is a long-term medical treatment designed to reduce a person’s sensitivity to specific environmental allergens. Unlike medications that primarily mask symptoms, this therapy works to retrain the immune system to tolerate these substances. The fundamental goal of allergen immunotherapy is to decrease the severity of allergic reactions and potentially lead to lasting remission of allergy symptoms, even after treatment concludes.
How Allergen Immunotherapy Alters the Immune Response
A typical allergic reaction begins when the immune system mistakenly identifies a harmless substance, like pollen or dust mites, as a threat. This leads to the production of allergen-specific IgE antibodies, which then attach to mast cells and basophils in the body. Upon subsequent exposure to the allergen, these cells release histamine and other chemicals, causing symptoms such as sneezing, itching, or wheezing.
Allergen immunotherapy works by introducing controlled, gradually increasing doses of the specific allergen into the body. This repeated exposure initiates a shift in the immune system’s response, moving away from the allergic Th2-type reaction. Over time, the immune system begins to develop a more tolerant Th1/Treg (regulatory T-cell) response.
This shift involves several molecular changes, including the increased production of “blocking antibodies,” specifically IgG4. These IgG4 antibodies intercept allergens before they can bind to IgE on mast cells and basophils, thus preventing the release of inflammatory mediators. Additionally, regulatory T cells produce cytokines such as interleukin-10 (IL-10) and transforming growth factor-beta (TGF-β), which further suppress allergic inflammation and promote tolerance.
The process also leads to the desensitization of mast cells and basophils, making them less reactive to allergen exposure. These cellular and humoral changes cumulatively contribute to a reduced allergic response, allowing the body to become accustomed to substances that once triggered severe reactions.
Types of Allergen Immunotherapy
Allergen immunotherapy is primarily delivered through two main methods, each with distinct administration characteristics. Subcutaneous immunotherapy (SCIT), commonly known as allergy shots, involves injections of allergen extracts. These injections are administered in a clinical setting, typically into the upper arm, by a healthcare professional.
Sublingual immunotherapy (SLIT) offers an alternative, involving tablets or drops placed under the tongue. After the first dose is given under medical supervision, this method can be self-administered at home. SLIT is absorbed through the lining of the mouth, providing a more convenient option for many patients.
When comparing the two, SCIT is considered more effective for a broader range of allergens and leads to stronger, more durable responses for conditions like allergic rhinitis or allergic asthma. However, it requires regular office visits, weekly during the initial phase. SLIT provides greater convenience due to home administration, which can improve patient adherence.
SLIT also has a more favorable safety profile, with reactions localized to the mouth and less frequent systemic reactions compared to SCIT. While SCIT involves less frequent, monthly injections during the maintenance phase, SLIT requires daily administration of the allergen. The choice between these methods depends on individual patient factors, including the type and severity of allergies, lifestyle, and preferences.
The Treatment Process and Timeline
The journey of allergen immunotherapy begins with a thorough allergy evaluation, which includes specific allergy testing. This testing, involving skin prick tests or blood work, helps identify the precise allergens that trigger a patient’s symptoms. Confirming these triggers is a necessary step before a personalized treatment plan can be developed.
Once the specific allergens are identified, the treatment proceeds through two main phases. The initial Buildup Phase involves gradually increasing doses of the allergen. For subcutaneous immunotherapy, injections are given once or twice a week, and this phase lasts between three to six months until a target dose is reached.
After the target dose is achieved, patients transition to the Maintenance Phase. During this phase, the allergen dose remains consistent, but the frequency of administration decreases. For allergy shots, this means injections every two to four weeks.
Patients receiving injections are monitored in the clinic for approximately 30 minutes after each dose. This observation period allows healthcare providers to identify and manage any immediate reactions, ensuring patient safety. The overall duration of a full course of allergen immunotherapy ranges from three to five years.
Who is a Candidate for Treatment?
Allergen immunotherapy is recommended for individuals experiencing symptoms from specific types of allergies. These include allergic rhinitis, referred to as hay fever, and allergic asthma, where allergens trigger respiratory symptoms. It is also a treatment for allergic conjunctivitis and individuals with severe reactions to insect stings, such as those from bees, wasps, or ants.
The allergens addressed by this therapy include various pollens (tree, grass, and weed), dust mites, pet dander from animals like cats and dogs, and mold spores. Traditional allergen immunotherapy is not used for food allergies, where strict avoidance remains the primary management strategy.
Candidates for treatment include individuals whose allergy symptoms are not adequately controlled by avoidance measures or standard medications. Patients who wish to reduce their long-term reliance on daily allergy medications, or those for whom allergen avoidance is impractical, may also find this therapy suitable. Both adults and children can receive allergen immunotherapy, although it is not recommended for children under the age of five due to difficulties with cooperation and articulating symptoms.