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IgE’s Role in Allergic Asthma

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Immunoglobulin E (IgE) is a type of antibody that is present in minute amounts in the body but plays a major role in allergic diseases. IgE binds to allergens and triggers the release of substances from mast cells that can cause inflammation. When IgE binds to mast cells, a cascade of allergic reaction can begin:

• Allergen exposure
Repeated exposure to a particular allergen can be the first step in developing a reaction to it. Some allergens trigger strong allergic reactions, while others trigger

• T cell action
Allergens induce T cells to activate B cells, which develop into plasma cells that produce and release more antibodies.

Binding of IgE to Mast Cells
The surfaces of mast cells contain special receptors for binding IgE. The IgE antibody fits to this receptor like a module docking with the mother ship. This arrangement is such that when two adjacent mast-cell-linked IgE antibodies are in place, the allergen is drawn to both and attaches itself to both, crosslinking the two IgEs. When a critical mass of IgEs become cross-linked, the mast cell releases histamine and other inflammatory substances, and the allergic cascade begins.

Your mast cells are like little bombs that are armed and ready for detonation.

The Allergic Cascade
Following exposure to an allergen, a series of initial reactions in the immune system occurs. This early-phase response is followed by a second, more severe reaction known as a late-phase response. Typically, the allergic cascade follows this pattern:

1. Sensitization to an allergen – being exposed for the first time
You might be initially exposed to an allergen by inhalation (of pollen, mold, dust mites, etc.), ingestion (swallowing a type of food or medication), touch (coming into contact with poison ivy, latex, or certain metals, such as nickel), or injection (receiving a medication or being stung by an insect).

Your body produces IgE designed specifically for that particular allergen, but you won’t experience a reaction yet. If you are atopic (meaning, you’ve inherited a predisposition toward allergic disease), your T cells are quick to stimulate B cells. When stimulated, B cells develop into plasma cells. Plasma cells produce IgE antibodies, which are targeted to that specific allergen, and the IgE binds to special receptors on mast cells. Your system is now sensitized. Your mast cells are like little bombs that are armed and ready for detonation.

2. Early-phase response upon reexposure to an allergen
When you are re-exposed to an allergen, the IgE of mast cells binds to the allergen, cross-linking the IgE. When enough cross-linking occurs, the mast cells explode with histamine and other inflammatory substances, called mediators. The mediators speed through your system.

Then it happens. You wheeze, sneeze, cough, get itchy eyes, have a runny nose, become short of breath – in other words, you experience the whole unpleasant range of symptoms known as the allergic response. And all of this occurs within an hour after initial exposure.

3. Late-phase response to an allergen
The late-phase response actually begins at the same time as the early-phase response, but it takes longer to see. In some individuals, the body rallies its immune system for this second phase, which can happen relatively soon after the initial reaction – anywhere from about three to ten hours later. Often, this late-phase response involves immune cells known as eosinophils, and it can last for 24 hours or so before subsiding. During the late-phase response, congestion and certain other symptoms can be more severe than those seen during the initial response.

Consequences of Chronic Allergic Reaction in Asthma
With repeated allergen exposure and allergic response, some damage can be done to the tissues involved. Long-term controller medications that aggressively attack inflammation and maintain maximum lung function may reduce the risk of permanent damage.

Although allergic disease is not curable, it is treatable enough to live with. Healthcare providers can be significant allies in this effort – particularly allergists, pulmonologists, and certain other specialists. In addition, many research organizations make studying allergic disease their top priority and can be excellent sources of information on the immune system. The more you know about how an allergic response occurs, the better armed you’ll be to meet its challenges.

 

Source: Asthma and Allergy Foundation of America, www.aafa.org

This article was originally published in Coping® with Allergies & Asthma magazine, July/August 2011.