Allergy and Immunology

Allergy and Immunology

Dr. Kennedy
Austrian pediatrician Clemens Pirquet (1874-1929) first used the term “allergy.” He referred to both immunity that was beneficial and to the harmful hypersensitivity as “allergy.” Now we refer to allergy exclusively as the harmful variety. The word allergy is derived from the Greek words allos, meaning different or changed combined with ergos, meaning work or action. Allergy thus refers to an “altered reaction.” The word allergy was first used in 1905 to describe the adverse reactions of children who were given repeated shots of horse serum to fight infection. In 1906 the term “allergy” appeared for the first time to represent this unexpected “changed reactivity.” Immunology refers to a somewhat more extensive knowledge of the immune system including its structure and function, disorders of the immune system, blood banking, immunization and organ transplantation. Doctors who specialize in allergy typically have a depth of knowledge about immunology.

An allergy can be thought of as a misguided reaction to foreign substances by the immune system, the body system of defense against foreign invaders, particularly pathogens (the agents of infection). The allergic reaction is misguided in that these foreign substances are usually harmless. The substances that trigger allergy are called allergens. Examples include pollens, animal danders, dust mite, molds, and certain foods. People prone to allergies are said to be allergic or atopic.

Although allergies can develop at any age, the risk of developing allergies is genetically based. It is related to ones family history of allergy. If neither parent is allergic, the chance for allergies is about 15%. If one parent is allergic, the risk increases to 30% and if both are allergic, the risk is greater than 60%.

Allergens cause the production of immunoglobulin E (IgE), an antibody everyone has in small amounts. Allergic persons, however, produce IgE in abnormally quantities. Normally, this antibody is important in protecting us from parasites, but not from other allergens. During the sensitization period in allergy, IgE is overproduced. It coats certain potentially explosive cells which contain chemicals, notably histamine. These chemicals cause inflammation and the typical allergic symptoms. This is how the immune system becomes misguided and primed to cause an allergic reaction when stimulated by an allergen.

The common allergic conditions are hay fever, asthma, allergic conjunctivitis (allergic eyes), allergic eczema, hives (urticaria), and allergic shock (anaphylaxis and anaphylactic shock).

Hay fever (allergic rhinitis) is the most common of the allergic diseases and refers to seasonal nasal symptoms provoked by pollens. Year round (perennial allergic rhinitis) is usually due to indoor allergens, for example dust mites or molds. Symptoms are secondary to inflammation of the tissues that line the inside of the nose after allergens are inhaled. Adjacent areas (ears, sinuses, and throat) can also be involved. The most common symptoms include:

  • Post nasal drip
  • Sneezing
  • Runny nose
  • Stuffy nose
  • Nasal itching
  • Itchy ears and throat

Asthma is a breathing problem caused by inflammation and spasm of the lung’s air passages (the bronchial tubes). This inflammation causes a narrowing of the air passages, which limits the flow of air into and especially out of the lungs. Asthma is most often, but not always, related to allergies. Common symptoms include:

  • Shortness of breath
  • Wheezing
  • Coughing
  • Chest tightness
  • Sneezing

Allergic eyes (allergic conjunctivitis) is inflammation of the white part of the eye and the inside of the eyelid and displays:

  • Redness under the lids and the sclera (white part of the eye)
  • Watery, itchy eyes
  • Swelling of the membranes

Allergic eczema is an allergic rash that is usually not caused by skin contact with an allergen and features the following symptoms:

  • Itching, redness, and or dryness of the skin
  • Rash on the face, especially children
  • Rash around the eyes, in the elbow creases, and behind the knees, especially in adults

    Hives (urticaria) are skin reactions that appear as itchy swellings. They may occur on any part of the body. Hives can be caused by an allergic reaction, such as to a food or medication, but they also may occur in non-allergic people. Typical hive symptoms are:

    • Raised red welts
    • Intense itching

    Allergic shock (anaphylaxis or anaphylactic shock) is a life-threatening condition which can affect a number of organs at the same time. It typically occurs when the allergen is eaten or injected (for example, a bee sting). Allergic shock is caused by dilated and “leaky” blood vessels, which result in a drop in blood pressure. Some or all of the following symptoms may occur:

    • Hives or reddish discoloration of the skin
    • Nasal congestion
    • Swelling of the throat
    • Stomach pain, nausea, vomiting
    • Shortness of breath, wheezing
    • Low blood pressure or shock

      Allergic eczema is an allergic rash that is usually not caused by skin contact with an allergen and features the following symptoms:

    • Itching, redness, and or dryness of the skin
    • Rash on the face, especially children
    • Rash around the eyes, in the elbow creases, and behind the knees, especially in adults

    Testing for Allergies

    Allergists often use skin tests to determine and guide treatment. A small amount of the suspected allergy-provoking substance (termed the allergen) is placed on the skin. The skin is then gently scratched through the small drop with a special sterile needle. An allergy skin test is also called a scratch test. If the skin reddens and, more importantly, if it swells, the test is positive and allergy to that substance is considered probable. A positive skin test implies that the patient has a IgE antibody on specialized cells in the skin that release histamine to cause redness and itching. (These cells are called mast cells and the IgE antibody bound to them is specific to the food being tested.) Skin tests are rapid, simple, and relatively safe. They can be very helpful in specifically identifying causes of allergies. In some extremely allergic patients who may already have had severe reactions (called anaphylactic reactions), skin testing cannot be used because it could evoke a dangerous reaction. Skin testing also cannot be done on patients with extensive eczema. If the test is positive, the allergist may order special blood tests, such as the ELISA and the RAST which measure the presence of specific types of IgE in the blood. These tests may cost more than skin tests, and results are not available immediately. As with skin testing, positive RAST and ELISA tests do not by themselves necessarily make the final diagnosis.

    Treatment of Allergies

    Allergists often recommend desensitization therapy. For an extended period of time, on a periodic recurring basis, the patient is given subcutaneous injections of allergens. These are referred to as desenitization shots. The idea is to expose the immune system to gradually increasing doses of extracts of the allergens a person reacts to on the scratch test with the intention of retraining the immune system not to over-react to these allergens. When carried out according to protocol, the success rate exceeds 80%.

  • Comments are closed.