Currently, there’s only one treatment that ‘cures’ allergies – desensitisation immunotherapy. This involves administering minute amounts of the allergen – either orally or via injection – and increasing the dose until tolerance is achieved. This method has been highly successful in treating grass pollen and insect venom allergies. It has been less successful with house dust mite and pet allergies. It is also relatively unsuccessful with food allergies and in some cases has triggered severe allergic reactions. Immunotherapy by injection of the allergen under the skin (known as SIT – systemic immunotherapy) should be done under hospital supervision. It usually takes 12 weekly injections to achieve tolerance. After this, monthly maintenance injections are required for a further three to five years. Immunotherapy taken orally, either as tablets or droplets under the tongue, is called sublingual immunotherapy (SLIT) and can safely be administered at home. These methods shouldn’t be confused with EPD (enzyme potentiated desensitisation), which is an ineffective procedure. For most allergies, the mainstay of treatment and management is specific allergen avoidance and, failing this, long-term, low-dose inhaled or topically applied steroids (cortisone) together with non-sedating antihistamine medication. Antihistamines have advanced and are now more specific to the histamine receptors in our tissues and less prone to unwanted side-effects, such as sedation and drying of mucous membranes. Inhaled and topical (applied to skin) steroids have also become more targeted and are now less likely to cause systemic effects, such as growth problems in children and osteoporosis or cataracts in adults.
Theophylline tablets have all but been withdrawn from use in treating asthma owing to unpredictable effects and lack of benefit. But a new generation of drugs called phosphodiesterase-4 inhibitors is an exciting development, as these may both open the airways and reduce lung inflammation. Drugs that act on specific chemicals involved in allergic inflammation are being developed (they are now widely available). These include leukotriene receptor antagonists, such as montelukast and zafirlukast, which block the effects of leukotrienes, the chemicals that promote allergic inflammation.
One of the most exciting developments in medical science this century is the so-called biological agents, or monoclonal antibodies. Patients with allergies have increased blood levels of the antibody IgE, which triggers mast cells to release histamine and other inflammatory mediators. If the effect of IgE is blocked, the allergic reaction is stopped in its tracks. Humanised monoclonal antibody proteins cling to free immunoglobulin IgE in the bloodstream and render it inactive, preventing allergies from developing. They also stick to the activation areas on mast cells preventing IgE from attaching, as well as reducing the overall manufacture of IgE in the body. The monoclonal antibody omalizumab is available as a treatment for asthma and rhinitis. Similar monoclonal antibodies can be used to prevent food allergic reactions by blocking the effect of IgE. These wonder proteins have a general ‘calming’ effect on many forms of inflammation, including arthritis, colitis and skin diseases. As with any new drug, they’re expensive. They also have to be given by injection – being proteins, they’d be digested and rendered inactive if taken orally.
A drawback of immunotherapy is that it carries a significant risk of triggering an allergic reaction. So if the allergy-provoking part of the allergen could be removed, while retaining the part our immune system recognises, the ‘neutralised’ allergen could be successfully desensitised without the risk of an unwanted reaction when it’s administered. Modified vaccines are in the final stages of development and could soon be mass produced for immunotherapy to many environmental allergens and foods. Researchers are also developing specific plasmid and short DNA protein vaccines, which appear even more effective if given while bound to ‘friendly’ probiotic or inactivated bacteria. Over the next ten years, doctors hope many conditions, such as allergic asthma, rhinitis and food allergies, will be cured by such vaccines.