Allergic vs. Non-Allergic
Paul M. O’Byrne, MD
Firestone Institute for Respiratory Diseases,
Department of Medicine, McMaster University,
Hamilton, ON, Canada
Dr. Paul M. O'Byrne, MD
Firestone Institute for Respiratory Diseases
Asthma is frequently characterized as “allergic” and “non-allergic”. Allergic asthmatic patients are, in general, younger and have a better response to conventional therapy, particular to inhaled corticosteroids (ICS). Allergic asthma has been very well characterized and airway dendritic cells, Th2 cells, mast cells, basophils, and eosinophils are important in its pathobiology. Non-allergic asthmatic patients are often adult onset; it is associated with non-allergic co-morbidities, such as rhinosinusitis and gasteroesophageal reflux, and is less responsive to ICS treatment. Exposure to small molecular weight occupational sensitizers is an important cause of non-allergic asthma and airway neutrophils are prominent. However, some studies have shown associations between asthma severity and serum IgE levels, even in “non-allergic” patients.
Therapy directed against IgE for asthma (omalizumab) had been demonstrated to improve asthma control, reduce asthma exacerbations and allow ICS dose reduction in allergic patients. It has not been evaluated in “non-allergic” patients. The use of other currently available asthma treatments does not distinguish between allergic and non-allergic patients. A more useful characterization for determining the treatment requirements of more severe asthmatic patients is to measure the airway inflammatory response, using induced sputum. Measuring sputum eosinophils has allowed the monitoring of doses of ICS treatment and a reduction in severe asthma exacerbations. Also, an anti-IL-5 mAb (mepolizumab) has been shown to allow prednisone reduction and reduce severe exacerbations in patients with severe asthma and a persisting airway eosinophilia. A similar approach in patients with a persisting airway neutrophilia may be possible with antagonists of the IL-8 receptor (CXCR2 antagonists).
Posted: March 2010
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