Breath of Fresh Air: Feature Articles

Chapter 3: What is an Allergic Reaction?

In our popular speech, the word allergy is used to refer to certain types of reactions that some but not all people develop to specific things in the world around us. Common allergic reactions are sneezing; itchy, watery eyes; red, itchy skin rashes; and, in the bronchial tubes of the lungs, asthma. There are medical terms for each of these allergic reactions. Medical personnel refer to "allergic rhinitis" (rye – NY - tis) when referring to allergic reactions of the nose; "allergic conjunctivitis" (con – JUNCT – i – VY - tis) when referring to allergic reactions of the lining of the eye; and "allergic dermatitis" (derm – a – TY - tis) when referring to allergic reactions of the skin. "Allergic bronchitis" would not be a bad expression to describe most asthma, but asthma (derived from the Greek word for panting) is the traditional term and it has stuck. Finally, "hay fever" is the popular term used to refer to seasonal allergic rhinitis and/or allergic conjunctivitis, even though these conditions generally have nothing to do with exposure to hay and are not associated with fever!

Allergy refers to a specific type of reaction made by the body in some people and not others.

Allergic rhinitis, conjunctivitis, dermatitis (also known as eczema), and asthma are commonly found together in various combinations in the same person and in families. The reason is that they share a common mechanism. The body reacts with similar defenses against the outside world in the eyes, nose, skin, and bronchial tubes.

The same allergic process can cause reactions in the nose, eyes, skin, and bronchial tubes.

The human body has developed a variety of different methods to react to the outside world. Some of these, such as allergic reactions to antibiotics like penicillin, represent different kinds of allergic responses that are unrelated to the asthmatic-like allergic reaction. Another familiar example, diarrhea that develops in some persons in response to dairy products, is now known to be due to an enzyme deficiency in the intestines and is considered a chemical intolerance (lactose intolerance) rather than a true allergy. Finally, in popular speech, we may use the word the allergy to refer to our reaction to things that we find irritating and unpleasant. Persons will describe themselves as allergic to cigarette smoke, for instance, or to strong odors. Although the symptoms that we experience may be similar to an allergic response, these are not true allergic reactions. The cells and chemicals involved with allergy are not involved with this response to irritants, and, unlike allergy, it is not unique to certain predisposed individuals. Thus, anyone with strong exposure to the smoke of a house fire will develop cough and chest tightness. This results from irritation of the bronchial tubes, not from allergy.

Medication allergies and other sensitivities are unrelated to asthmatic-like allergies.

What then constitutes a true allergic reaction? We start first with the allergen (AL – ler - gen). In asthma, when these substances are inhaled into the lungs, they elicit a characteristic (allergic) reaction from the bronchial tubes. Common allergens include animal danders; pollens of grasses, trees, and common weeds; and spores of various molds and fungi. Some persons may encounter allergens in their workplace, such as the baker who becomes allergic to flour dust and develops "bakers' asthma." Other substances that we commonly breathe in, including air pollutants, appear to be of the wrong size and shape to function as allergens; and although they may cause considerable misery, they do not cause allergic reactions.

Most allergens important in asthma are breathed in.

Although we all breathe in house dust, only in certain persons make an allergic reaction to it. In those persons with asthma and house dust allergy, the body has made specialized proteins that are attracted to the allergen and attach to it firmly. These specialized proteins are called antibodies (ANT – i – bod -ies). Why certain persons make these antibodies and others do not is unknown, although the tendency clearly appears to be an inherited one passed in the genes from one generation to the next.

Persons with allergies make a special kind of antibody that recognizes specific allergens.

Antibodies attach firmly not only to in coming allergens but also to a specific type of cell present in your bronchial tubes, called the mast cell. Mast cells are important because they are factories for the chemicals that produce the asthmatic-type inflammation of the bronchial tubes. If you have asthma and are allergic to house dust allergens, your bronchial tubes are laden with mast cells on which sit antibodies specifically engineered to recognize the house dust allergen.

In asthma, allergy (mast) cells covered with antibody wait in the bronchial tubes, ready to recognize certain inhaled allergens.

Imagine then this scenario. You shuffle across the bedroom carpet and lie down on the old mattress, releasing house dust allergens into the air. You breathe the house dust allergens into your lungs and there, waiting on the surface of mast cells in your bronchial tubes, are antibodies that recognize this allergen and bind to it. When the antibody binds the allergen, the mast cell receives a signal, and it explosively releases packets of inflammatory chemicals. Among the actions of these chemicals are stimulation of the muscles that surround the bronchial tubes, causing them to narrow; attraction of other inflammatory cells out of the blood stream and into the bronchial tubes; leakage of fluid out of the blood vessels and into the bronchial walls causing them to become swollen; and stimulation of mucous glands to release mucus into the bronchial tubes. You can see that the stage is set for an asthmatic attack and worsened inflammation of the bronchial tubes.

Sometimes you can avoid the allergens to which you make reactions.

Do not despair. Knowledge is a powerful weapon to help us protect ourselves against a world of allergens and against the allergic responses of our bodies to this outside world. Already you can see how one might prevent the allergic asthmatic reaction that we have just described. Best would be to avoid breathing in the house dust allergens, and there are many methods — to be discussed in future issues of Breath of Fresh Air — to achieve this. In addition, pharmaceutical companies are working to design drugs that block many of the steps in the allergic process, from blocking production of the antibodies to the house dust allergen; to blocking those antibodies from binding to the surface of mast cells; to preventing mast cells from releasing their inflammatory chemicals when allergen and antibody meet; to blocking these chemicals from exerting their effects. Some of these medications are already available to treat asthma. Others represent active areas of ongoing scientific investigation, and they will likely translate into future asthma therapies within our lifetime.

Medicines can be used to interrupt the allergic reaction at various steps along the process.