From the Guidelines
The main driver of allergic (extrinsic) asthma is exposure to external allergens, particularly inhalant allergens such as dust mites, pet dander, mold spores, and pollen, which trigger an immune response in susceptible individuals. These allergens can be found in various environments, including homes, schools, and workplaces, and can be carried on clothing, bedding, and other materials. When a person with extrinsic asthma encounters these triggers, their immune system overreacts by producing immunoglobulin E (IgE) antibodies, which bind to mast cells and basophils 1. Upon subsequent exposure, these cells release inflammatory mediators like histamine, leukotrienes, and prostaglandins, causing bronchial smooth muscle contraction, increased mucus production, and airway inflammation. This cascade results in the characteristic symptoms of asthma: wheezing, coughing, chest tightness, and shortness of breath.
Some of the most common indoor allergens that contribute to extrinsic asthma include:
- Dust mites, which are found in bedding, carpets, and upholstered furniture 1
- Pet dander, particularly from cats and dogs, which can become airborne and be carried on clothing and other materials 1
- Mold spores, which can grow in damp environments and be found in basements, bathrooms, and kitchens
- Pollen, which can enter homes through open windows and doors or on clothing and other materials
Management of extrinsic asthma typically involves avoiding identified triggers, using controller medications like inhaled corticosteroids (such as fluticasone or budesonide) daily, and having rescue medications like albuterol available for acute symptoms. For severe allergic asthma, biologics targeting IgE (omalizumab) or specific inflammatory pathways may be prescribed. Understanding this allergic mechanism is crucial because it distinguishes extrinsic asthma from intrinsic asthma, which is triggered by non-allergic factors like respiratory infections or exercise. Effective allergen avoidance requires a multifaceted, comprehensive approach, including reducing indoor relative humidity, replacing carpets with polished wood flooring, and using high-efficiency particulate air (HEPA) filters to reduce airborne allergens 1.
From the FDA Drug Label
Omalizumab inhibits the binding of IgE to the high-affinity IgE receptor (FcεRI) on the surface of mast cells, basophils, and dendritic cells, resulting in FcεRI down-regulation on these cells In allergic asthmatics, treatment with omalizumab inhibits IgE-mediated inflammation, as evidenced by reduced blood and tissue eosinophils and reduced inflammatory mediators, including IL-4, IL-5, and IL-13.
The main driver of allergic (extrinsic) asthma is IgE-mediated inflammation. Omalizumab works by inhibiting the binding of IgE to the high-affinity IgE receptor, which reduces inflammation and alleviates symptoms of allergic asthma 2.
From the Research
Allergic (Extrinsic) Asthma Drivers
- The main driver of allergic (extrinsic) asthma is exposure to indoor allergens, such as those derived from cats, dust mites, and cockroaches 3, 4.
- Studies have shown that high levels of exposure to these allergens increase the risk of sensitization and symptomatic asthma 3.
- The risk of sensitization to allergens is restricted to patients who are exposed to high levels of these allergens 3.
- Allergen-induced immune responses, including the production of IgE and the activation of T helper type 2 (Th2) cells, play a key role in the development of allergic asthma 5.
Role of Allergens in Asthma Development
- Exposure to allergens, such as house dust mite (HDM) and birch pollen, can trigger innate and adaptive immune responses and cause oxidative stress damage in the airways 6.
- The combination of exposure and sensitization to an allergen is significantly associated with acute asthma 4.
- Clinical studies have shown a direct quantitative correlation between dust mite allergen exposure and the prevalence of both sensitization and asthma 4.