Asthma, a highly prevalent chronic inflammatory disease, affects 330 million people worldwide, including 35 million people in the U.S. alone, according to the World Health Organization. It is a complex syndrome that initiates an immune response after allergen exposure that leads to intermittent attacks of breathlessness, coughs, wheezing, swollen airways and hypersensitivity.
Allergic Asthma
Allergic asthmatics tend to have a family history of allergies, such as allergic rhinitis, hay fever or eczema. Allergic asthma is a complex disease resulting from environmental factors and multiple genetic interactions. These include an allergic reaction to allergens such as pollen and pet dander. Seasonal asthma usually affects people in the spring or early autumn. Symptoms are worse in the spring due to increased flowering plants, or in the late summer or early fall due to ragweed or mold from leaves on trees. Allergens induce airway inflammation, swelling and tightening of the muscles around them. This narrows the airways, reducing airflow into the lungs. Cells lining the airways make more mucus than normal to remove the allergen, but this response also narrows the airways further.
Initial Immune Response
The immune response underlying asthma involves several steps. This includes the initial sensitization to allergen, then early and late phase responses. First exposure occurs commonly by inhalation, touch, ingestion or insect sting. Specific immunoglobulin E, or IgE, antibodies are produced that bind to the allergen and present it to specific receptors on mast cells of the immune system.
Amplification of Response
In asthma sufferers, subsequent stimulation by the same allergen causes a strong immunological cascade. This begins with the accumulation of allergen-bound IgE on the mast cell receptors and the release of mediators such as histamines and leukotrienes that recruit other immune cells. A specific subset of T-helper immune cells stimulate B cells to develop into plasma cells that produce more IgE antibodies. These target the specific allergen, causing a subsequent response that further stimulates generation of cell-producing chemicals that mediate the recruitment of more immune cells.This amplification of the immune response or inflammatory cascade in the lungs causes the allergic asthmatic attack.
Therapeutic Approaches
Allergic disease is currently incurable but can be managed. Asthma medicines can be taken in pill form, but most are taken using a device called an inhaler that allows the medicine to go directly to your lungs. Inhaled corticosteroids are the most effective option for long-term relief of the inflammation and swelling and are the preferred medicines for long-term control of asthma, according to the National Heart, Blood and Lung Institute. Reducing inflammation prevents the cascade of events associated with asthma. Although many clinical trials are under way, continued research to enhance the current understanding of how allergens generate immune responses is critical for the development of novel approaches to effective treatment and prevention of allergic asthma.
References
- American Academy of Allergy, Asthma and Immunology: Asthma Statistics
- "Journal of Allergy and Clinical Immunology"; John W. Holloway, et al.; February 2010
- GlaxoSmithKline: Types of Asthma
- Asthma and Allergy Foundation of America: IgE's Role in Allergic Asthma
- National Heart Blood and Lung Institute: What Is Asthma?
- World Health Organization; GARD Book; 2007
