THE PREVENTION and control of asthmatic symptoms (in children and adults) is attainable by environmental precautions, pharmacotherapy and allergen immunotherapy. Specific allergen immunotherapy (SIT), previously known as desensitisation and hyposensitisation, modifies the immune system to produce a good evidence that SIT is clinically effective in the treatment of seasonal or perennial allergic rhinitis and asthma.
The prevalence of asthma and allergy is increasing. It is estimated that more than 40 per cent of the world's population is atopic (have a genetic predisposition to develop hypersensitivity reaction). Asthma occurs in around 10 to 15 per cent of the paediatric population and is estimated to affect between 100 to 150 million people worldwide. About 50 per cent of adult asthmatics are atopic. Although the aetiology of non-atopic asthma is less well defined, similar inflammation is present in the lungs of non- atopics and atopics and the same drugs treat both diseases.
Some workers report 80 per cent of asthmatic children as being allergic as well as 50 per cent or more of adult asthmatics. A study of IgE antibody levels in asthmatics indicated that asthma is almost always associated with some type of IgE-related reaction and therefore has an allergic basis. These investigators reported that their findings challenged the concept that there are basic differences between so-called allergic ("extrinsic") and non-allergic ("intrinsic") forms of asthma.
Whereas earlier work focused on circulating antibody, newer studies suggest that SIT acts by modifying T cell responses. Immunotherapy also reduces inflammatory cell recruitment and activation and mediator secretion.
Immunotherapy and allergen avoidance are the only treatments that may affect the natural course of allergic diseases. A meta-analysis of studies of immunotherapy in the treatment of asthma, showed that allergen immunotherapy significantly reduced asthma symptoms and reduced patients' medication requirements. Although there was a trend towards improved lung function for the treated groups, this did not achieve statistical significance. There was an overall reduction in airway hyperactivity following immunotherapy.
A report from the Mayo Clinic on 79,593 immunotherapy injections over a 10-year period revealed the incidence of adverse reactions to be less than one per cent. Most of the reactions were mild and responded to immediate medical treatment. There were no fatalities. In Jamaica, since the start of SIT in 1975, between 2,000 and 3,000 asthmatics have received immunotherapy, with good symptom remission. There have been no fatalities.
- Dr. A.W.W. Lawrence, allergist.
