Lauren, an 18-year-old college student, used to have a mildly runny and stuffy nose, mostly in the fall.  While on spring break, she spent several hours at an outdoor barbecue and developed episodes of sneezing, runny nose, and itchy, watery eyes.  She wondered “Am I allergic to something in the air?  Why is this not happening to my friend, Erica?”

What is an allergy?  An allergy is defined as an “abnormal sensitivity to a substance that is normally tolerated and generally considered harmless, such as pollen, food, drugs or even an insect sting.  This means that while some substances are well tolerated by most people, they can induce an adverse reaction (allergic reaction) in others, mainly due to the presence of the IgE antibody.

What is an IgE antibody?  First, we need understand our immune system.  B lymphocytes, with the help of T lymphocytes and macrophages, can produce five separate and distinct classes of immunoglobulins (antibodies), IgA, IgG, IgM, IgD and IgE.

Despite its presence in our body in only a minute quantity, IgE is a key player in allergic reactions.  The reason why some substances (allergens) have the ability to induce IgE production, and others substances (non-allergens) do not, or why only some individuals develop an allergic reaction after exposure to some particular allergens, is still not fully understood.  However, we do know that genetic predisposition plays a significant role in developing allergic conditions.  For example, children whose parents have allergic rhinitis, asthma, or eczema have a significantly increased likelihood of developing the same conditions.

Take Lauren’s case.  Her mother has a history of eczema and allergic asthma.  Lauren has inherited the ability to produce IgE to tree pollen.  After exposure for a period of time, she produced the specific IgE to tree pollen that bound themselves to the surface mast and basophil cells in the lining of her nose and conjunctiva.  The mast and basophil cells immediately released a variety of potent chemical mediators (histamine, leukotriene and prostaglandins) after tree pollen attached to specific IgE.  It caused her sneeze, have a stuffy and runny nose, and itchy, watery eyes.  Unlike Lauren, Erica did not produce IgE to tree pollen.  For her, tree pollen is not an allergen and would not cause the symptoms that Lauren has experienced.