Priming, Super Sensitivity and Deferred Reactions

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Category: Allergic Rhinitis and Sinusitus Published on Thursday, 10 July 2008 Written by Yong Tsai, MD
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This past Labor Day weekend, Matt, a thirty year old with a long history of seasonal allergic rhinitis and asthma in the fall, attended his new girlfriends’ family picnic.  Shortly after arriving, Matt began to develop a runny nose and sneezing.  But after pestered by these symptoms for several hours outdoors, they gradually subsided.

When the picnic ended, Matt went to his girlfriend’s apartment to watch a movie. Unfortunately, he began sneezing again because his nose, which was already irritated, was very sensitive to her perfume.  When her cat approached him, he sneezed some more.  Matt began wondering if the ragweed pollen followed him into her house.  He had no problems with her perfume or cat before.  So, why tonight?

Our body has two phases of allergic response that involve inflammatory cells and powerful chemical mediators. As we know, allergic reactions are linked to allergen-IGE-inflammatory cells called chemical mediators that induce almost immediate allergic symptoms.  Typically sneezing, runny nose, nasal congestion, and itching of the nose, throat or palate is peaks rapidly, but subsides within two hours or so.

The deferred phase reaction usually appear about 4 to 6 hours after allergen exposure, and up to 8 hours in some cases. When prior exposure creates a reaction, the already irritated mast cells become super sensitive, as Matt became with the perfume and cat.  When this happens, the eosinophylls are called into action, for a second rally against the allergens, even hours after you think you’ve recovered from a prior reaction, and inflammation occurs.

Patients and physicians both have noted a phenomenon, termed “priming”, that encompasses a patient’s worsening of symptoms at lower levels of exposure (low pollen count) as the season progresses, than they experienced earlier in the season with higher levels of exposure (high pollen count).

In other words, it takes less pollen in the air to initiate an allergic reaction late in the pollen season than it did at the beginning of the season. “Primed” patients noted that they are more reactive to lower levels of exposure to other allergens: dust, molds, mites and animals.

The longer one seems to be bothered by allergic nasal symptoms, the more one’s nose is twitched or symptoms are triggered by non-specific, non-allergic factors, such as pollutants, smoke, powders, cosmetics, and newsprints.

He is experiencing priming.  As a pollen season progresses, it takes less exposure to specific pollen as well as other allergens to trigger symptoms.  His allergy to dust may not be sufficient to trigger your symptoms by itself, but once your nose becomes hyper responsiveness during ragweed season, it will become reactive to the dust that did not bother you before.

Although the reaction triggered by irritant is not IgE mediated, they still increase injury to already sensitive area.  If you continuously exposed to allergens and irritants, a vicious cycle can develop.  The symptoms caused by irritant may be similar to those caused by an allergen.  Irritant stimulate your nose’s nerve ending, which transmit signals to the brain, which relays a message to your nose to swell, run or sneezing.

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