Allergen Immunotherapy (AIT), commonly known as allergy shots, is a long-term treatment for severe or persistent allergies. A common concern is whether this therapy weakens the immune system. AIT does not suppress or compromise the body’s ability to fight off infections and diseases. Instead, it precisely modulates the immune system, reprogramming its response to a specific allergen. The goal is to correct the misdirected reaction that defines an allergy, strengthening tolerance rather than weakening defenses.
Understanding the Allergic Immune Response
An allergy is an inappropriate reaction by the immune system to an otherwise harmless substance, such as pollen or pet dander. This hypersensitivity is primarily driven by Immunoglobulin E (IgE) antibodies. IgE antibodies are produced after initial exposure and attach themselves to specialized immune cells, primarily mast cells.
Mast cells are abundant in tissues like the skin, lungs, and nasal lining. When re-exposed to the allergen, the substance binds to the IgE antibodies anchored on the mast cells. This binding causes the mast cells to rapidly release inflammatory chemicals, most notably histamine. The immediate release of these mediators causes the familiar symptoms of an allergy, such as itching, swelling, sneezing, and wheezing.
The Mechanism of Tolerance Induction
AIT works by introducing small, controlled doses of the specific allergen over an extended period. This repeated exposure teaches the immune system to stop viewing the allergen as a threat. The core immunological change involves shifting the balance of T-helper (Th) cells. While allergic individuals are dominated by T-helper 2 (Th2) cells that promote IgE production, AIT fosters the development of T-regulatory (Treg) cells and T-helper 1 (Th1) cells.
Treg cells are the mediators of tolerance, actively suppressing the allergic cascade. They secrete anti-inflammatory cytokines, such as Interleukin-10 (IL-10) and Transforming Growth Factor-beta (TGF-\(\beta\)). These cytokines inhibit Th2 cell function and dampen mast cell activity, shutting down the allergic reaction. A second change is the induction of allergen-specific Immunoglobulin G (IgG) antibodies, particularly the IgG4 subclass. These IgG4 antibodies act as “blocking antibodies” by intercepting the allergen before it can bind to IgE on mast cells, preventing the release of inflammatory mediators and allergic symptoms.
Allergy Shots Versus Immunosuppressive Drugs
The confusion about AIT often stems from comparing it to traditional immunosuppressive medications. True immunosuppressive drugs, such as high-dose systemic corticosteroids or chemotherapy agents, broadly suppress the entire immune system. These drugs indiscriminately reduce the activity of many immune cells, leaving a patient vulnerable to infections and impairing healing.
Allergen immunotherapy functions as a targeted immune modulator rather than a broad suppressor. AIT is highly specific to the allergen being treated, modifying the response only to that particular substance. The treatment normalizes the immune system’s reaction to the allergen while leaving all other aspects of immune defense fully functional.
Risks and Long-Term Effects of Treatment
While AIT does not weaken the immune system, it carries treatment-related risks. The main safety concern is the potential for an allergic reaction, since the treatment administers the substance the patient is sensitive to. Most reactions are minor and localized, involving redness, swelling, or itching at the injection site, and typically resolve within a few hours.
A more serious, though rare, risk is a systemic reaction, including anaphylaxis. Because of this possibility, allergy shots must always be administered in a medical setting, followed by an observation period of at least 30 minutes. This precaution ensures that any severe reaction can be immediately treated with emergency medication, such as epinephrine.
The long-term outlook for AIT is favorable, demonstrating a sustained, disease-modifying effect. The full course of treatment requires a commitment of three to five years to achieve a durable change in immune memory. After this period, many patients experience sustained relief from symptoms, often lasting for years after treatment is stopped. AIT has also been shown to potentially prevent the development of new allergies and, in children with allergic rhinitis, may reduce the risk of developing asthma.