The same system that helps protect you from infections, your immune system, can also be responsible for your worsening asthma. You may notice that at the same time you have that runny nose, watery eyes and sinus congestion, your peak flows are lower, you are wheezing more, and you may experience more shortness of breath. So how are my immune system and asthma linked?
The immune system normally protects you against foreign bacteria and viruses. In asthma and other allergic diseases, the immune system may be the cause for your worsening symptoms.
Many asthmatics are atopic (an inherited a predisposition towards allergy) where your immune system develops an exaggerated response to certain foreign substances or allergens. Your body's immune system senses these allergens, perceives them as foreign, and begins to prepare to fight off them off as a foreign intruder. The process that takes place is often referred to as the allergic cascade, which generally occurs in 3 steps:
- Early phase response
- Late Phase response
Sensitization- Allergen Exposure
The first time you are exposed to an allergen, sensitization, you will not usually have symptoms. You may be exposed to allergens that stimulate the allergic cascade through:
- Inhalation of substances such as dander, pollen or dust mites where the substances bind to membranes in your lung
- Ingestion of foods or medicines where the initial immune system reactions occur in the stomach
- Physical contact of skin with substances such as poison ivy
Immunologically, your body senses the allergen as foreign and sets off a cascade of events stimulating several different types of immune cells (see diagram):
- T cells rapidly stimulate B cells
- B cells transform into plasma cells
- Plasma cells produce IgE antibodies specific to the allergen
- IgE antibodies bind to mast cells
At this point, the allergen has triggered the allergy cascade, but you will not develop any symptoms or even realize that anything has happened. During subsequent exposures to the allergen, you may develop asthma symptoms as part of the early-phase response.
Early Phase Response- Re-exposure
With re-exposure to the allergen your immune system senses the allergen as foreign leading to:
- The mast cell/ IgE complexes produced in the sensitization phase, binding to the allergen thinking that it is a foreign invader
- Mast cells then release inflammatory cells called mediators (e.g. histamine) that quickly travel throughout your body with the purpose of fighting off the foreign invaders such as bacteria and viruses.
- You begin to experience symptoms of your body’s overreaction to the allergen.
The mediators react in different parts of your body causing your allergy symptoms. You may begin wheezing, coughing or feeling short of breath as the immunologic response causes swelling and narrowing of the airways in your lung. You may only experience runny nose or watery, itchy eyes. The immunologic response begins nearly immediately with symptoms occurring very shortly after re-exposure lasting 3-4 hours.
Late Phase Response
Beginning at the same time as the early phase response, but not causing symptoms for several hours, is the late phase response. Mediators released by the re-exposure to an allergen also stimulate other kinds of immune cells called eosinophils. Eosinophils contain substances that when released normally fight off infections, but in asthma, the cells damage the lung causing more inflammation and worsening symptoms.
In the late phase, symptoms will not develop for at least 4 hours, but may last as long as 24 hours. Increased inflammation and obstruction of airflow may be more severe than what is seen during the early phase.
So How Does Understanding The Allergic Cascade Benefit Me
Current therapies generally target specific parts of the cascade.
The most obvious approach would be to avoid the allergens altogether and prevent the allergic cascade from occurring. While this may work for some allergens like specific foods and pet dander, other allergens like dust and molds may be more difficult, and medications are often needed.
First generation antihistamine drugs like diphenhydramine (Benadryl) or second-generation antihistamines like loratadine (Claritin) or ceterizine (Zyrtec) prevent allergy symptoms by inhibiting the inflammatory response of the mediators released during the early phase of the allergic cascade. Antihistamines prevent mediators, such as histamine, from binding to receptors in the nose and eyes that cause the allergic symptoms of sneezing, runny nose, congestion and watery eyes.
bronchodilators like Albuterol target the early phase of asthma causing a widening of the airways and relief of airway obstruction making it easier to breathe. Drugs with anti-inflammatory properties, such as steroids and leukotriene antagonists, may be used acutely to decrease the late phase response or used a preventive measure to attempt to keep the late phase response from occurring at all.
Finally, allergy shots or immunotherapy may be used in an attempt to desensitize a patient to an allergen. With the shots your body decreases its foreign invader response- the immune system generates less IgE and hopefully does not react a strongly to a particular allergen.
Hopefully, a better understanding of your immune system will give you a better understanding of what might causing your asthma symptoms to worsen and help you gain better control.
Asthma and Allergy Foundation of America (AAFA). Consumer Information. Accessed: January 1, 2009. IgE's Role in Allergic Asthma
National Heart, Lung, and Blood Institute. Accessed: January 1, 2009. Expert Panel Report 3 (EPR3): Guidelines for the Diagnosis and Management of Asthma