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Allergen immunotherapy (also termed hyposensitization therapy, immunologic desensitization, hyposensibilization, or allergen-specific immunotherapy) is a form of immunotherapy for allergic disorders in which the patient is vaccinated with increasingly larger doses of an allergen (substances to which they are allergic) with the aim of inducing immunologic tolerance. Allergen specific immunotherapy is the only treatment strategy which treats the underlying cause of the allergic disorder. It is a highly cost-effective treatment strategy which results in an improved quality of life and a reduction in allergic- and allergen-related asthma, as well as a reduction in days off school/work. Immunotherapy has been shown to produce long-term remission of allergic symptoms, reduce severity of associated asthma as well as reduce the chances of new sensitizations to allergens developing. This is achieved via immunotherapy modulating the immune system response to allergens.

Allergen immunotherapy can either reduce the need for medication, severity of symptoms or eliminate hypersensitivity altogether. Therapy can be administered under the tongue (sublingually) or by injections under the skin (subcutaneous). Allergen-specific immunotherapy is the only known treatment option that is known to modify the allergy disease process (with a possible chance of curing the disease), whereas other therapies merely suppress the symptoms. Subcutaneous injection immunotherapy has been shown to be highly efficacious treatment for allergic disease, but due to a rare serious side effect of anaphylaxis, its use is restricted to specialist centers. As a result there has been growing interest in the sublingual therapy which can be safely administered at home.

Allergic rhinitis is an extremely common disorder. Over half of people receiving symptom based treatments report that they only get partial or a poor benefit from symptomatic based treatments. For these patients immuno-desensitisation therapy can be recommended. Subcutaneous injection based immunotherapy is one effective route but is complicated by rare but serious side effects. As a result of these rare but serious side effects the sublingual route for allergen vaccination immunotherapy is gaining increasing popularity among allergy specialists due to its lack of serious side effects.

Immunotherapy administered through cutaneous injections or sublingually has substantial empirical support. Numerous research articles and several meta-analytic studies support its clinical effectiveness. Immunotherapy can lead to a substantial decline in allergen symptomatology leading to a significant improvement in quality of life for allergy sufferers. Repeated courses of immuno-desensitisation leads to further reduction in allergy disease severity. Immunotherapy is superior to antihistamines and topical steroids in reducing severity of allergy symptoms and has been found to be a cost effective treatment strategy. Immunotherapy results in less time taken off work compared to those who rely solely on symptomatic relieving medications. In the case of grass allergy immunotherapy the pollen from the grass species used has strong cross reactivity between the various grass species thus meaning that treatment leads to desensitization to all grass species.

Sublingual specific immunotherapy has the benefit of allowing treatment to be carried out in the home environment and has been found to be a cost effective treatment strategy for allergic disorders. Sublingual immunotherapy cost effectiveness is significantly increased due to the reduced number of medical visits compared to those receiving subcutaneous injection based immunotherapy. For example those receiving subcutaneous injections make almost seven times more visits than those receiving home based sublingual immunotherapy versus those receiving subcutaneous injections that require frequent visits to doctors to receive their regular injections. Furthermore the sublingual route appears to be equally as effective as the subcutaneous route in trials of grass allergy.

Benefits from immunotherapy

Current antihistamines do not prevent allergic reaction, but instead block the action of histamine in the body, reducing allergic symptoms. Immunotherapy, in contrast, trains the immune system to tolerate allergic triggers by means of gradual exposure to increasing amounts of the offending allergen. The benefits of allergen specific immunotherapy are long lasting unlike symptomatic based treatments. Immunotherapy is most effective for pollen, dust, and animal dander allergies, and may help those with asthma.

Research in children aged from 5 years old to 16 years old shows similar effectiveness in the treatment of grass allergy as seen in adults. Like in adults allergen related asthma also decreases as well as allergic rhinitis symptoms. Recent studies in children suggest that if immunotherapy is commenced soon after allergies first develop, it may actually reduce the risk of developing allergic reactions to other allergens, and even reduce the risk of later developing asthma.

Mechanism of therapeutic action

Even the most allergic individual can tolerate minuscule amounts of an allergen without experiencing symptoms. Immunotherapy commences with the subcutaneous injection of a tiny amount of offending allergen, and gradually increases the dose until the individual’s immune system is essentially ‘retrained’ to tolerate exposure without producing an allergic response. This process is also known as specific immunotherapy.

Immunotherapy via repeated exposure to a specific allergen via either sublingual or subcutaneous route leads to a desensitization to the allergen and thus a reduction in allergic symptomatology and use of symptomatic based treatments. The exact mechanism is not fully understood but it is accepted that immunotherapy causes modification of the immune system. This modification leads to changes in IgE synthesis and the production of IgE blocking antibodies which thus reduces the immune systems allergic response to specific allergens.

Procedure For benefits to be felt from either sublingual or injection based allergen specific immunotherapy it needs to be started 2 – 4 months before the start of the allergen season in the case of seasonal allergies. The earlier it is started the better the level of allergy protection. Sublingual immunotherapy is a safe and effective alternative to injection based immunotherapy and can be administered in the home environment. Modest benefits have been demonstrated within the first season of therapy. Treatment needs to be continued for at least 3 years to achieve maximum effectiveness in immune desensitization to the allergen. In the case of sublingual immunotherapy there is no need to do a titrated graduated updose and therapy is generally started at the usual clinical dose.

Immunotherapy via the subcutaneous route involves the use of small hypodermic syringes which are used to inject commercial allergen extracts. Injections are normally given into the loose tissue over the back of the upper arm, half way between the shoulder and elbow. Injections are given under the skin (“subcutaneous”). This is the least painful place to inject allergen, as there are few nerve endings in the skin. When given correctly, the injections should be only slightly uncomfortable. They are not normally painful and are usually well tolerated by adults and teenagers. Some doctors may advise you to take an antihistamine a few hours before each injection to reduce the likelihood of local discomfort and other side-effects.

Allergy injections are started at very low doses. The dose is gradually increased on a regular (and usually weekly) basis, until a “maintenance” dose is reached. This usually means four to six months of weekly injections to reach the maintenance dose. Once the maintenance dose is reached, the injections are administered less often (every two to four weeks), still on a regular basis. Maintenance injections are normally given once per month for a few years. Generally, the longer the treatment and the higher the dose, the greater the therapeutic benefit.

After successful completion of immunotherapy, long-term protection can be expected for a period of 3–5 years or more. Therapy can be repeated should symptoms begin to return or if the individual becomes exposed to new allergens that were not included in the previous treatment regiment. This form of treatment is covered by the vast majority of insurance companies in the United States, because allergy vaccine injections have a strong evidence base for clinical effectiveness.

Copied and Adapted form Wikipedia