It's Spring Again and Allergies Are In Bloom : Part 2

by Food and Drug Administration (FDA)

(Page 2 of 2)

An Overachiever Immune System

Seasonal allergic rhinitis — hay fever — is the most common allergic disease. Its medical name means inflammation of the membrane lining the nose caused by exposure to an allergen at specific times of the year. (Hay is almost never its cause, and fever is not one of its symptoms, but the misnomer has stuck since it was coined more than 160 years ago.) Research, most of it in the 20th century, has demonstrated that allergy is actually an altered or exaggerated immune response. In an allergy-prone person the immune system reacts powerfully to foreign substances, such as pollen, that simply do not bother most of us.

The phenomenon of immunity has long been recognized. Ancient scribes reported that survivors of plague seemed to be protected if the disease struck again. Fifteenth century Chinese and Arab physicians tried injecting people with pus taken from smallpox victims. Sometimes the result was a mild case of smallpox that protected against the more serious form of the disease. Sometimes, too, the outcome was severe smallpox and death.

Two centuries ago, an English physician named Edward Jenner successfully immunized a young boy against smallpox by injecting him with a fluid from a cowpox sore — hence the term vaccination — from vacca, Latin for cow. But it was not until the late 19th and early 20th centuries that scientists began to explore the immune system and discover that it is responsible for a number of illnesses, including allergies.

The mechanisms by which the human body recognizes its own components and distinguishes them from foreign substances are among the most elegant products of evolution. Although they do not understand it fully, scientists believe the immune system consists of two main branches. One works through the action of white blood cells called T lymphocytes, or simply T cells. T cells attack foreign materials directly and also produce substances that summon other parts of the immune system to help destroy an invader. A deficit of T cell-mediated immunity is characteristic of acquired immune deficiency syndrome.

The other branch of the immune system is the one we associate with antibodies — highly specialized proteins manufactured by B lymphocytes — and antigens — enzymes, toxins, or other foreign substances that provoke a response from the body. When B cells encounter antigens, such as those on the surface of bacteria, they multiply and produce antibodies that destroy the invading germ or make it vulnerable to attack by other parts of the immune system. Once B cells have learned to make an antibody against a specific antigen, they go on making it indefinitely. This is why vaccines can induce permanent immunity against some diseases.

Ironically, it is the immune system's ability to maintain constant readiness against a repeat onslaught by an antigen that makes millions of people susceptible to allergic disease. For reasons that are not entirely clear, some antigens cause B cells to make a kind of antibody called immunoglobulin E — IgE for short. (Antigens that provoke IgE formation are referred to as allergens because they can cause an allergic reaction.) The first time an allergy-prone person is exposed to an allergen — pollen or house dust for example — the B cells respond by making IgE antibodies tailored to counteract the allergen. These IgE antibodies attach themselves to mast cells that are abundant in the respiratory tract, digestive system, and skin and to basophils, cells circulating in the blood.

The next time an allergen and its IgE antibodies come together, mast cells and basophils release powerful substances called mediators, among them histamine, that cause the allergic reaction. These mediators are fairly rapidly neutralized by the body. But as long as the allergen is present, histamine and other mediators will continue to be released from mast cells and basophils, and the patient's allergy symptoms will persist.

No one knows for sure why some people have allergies while most do not. Genetics appears to play a part; people who suffer from allergies usually have a close relative with similar problems. Susceptibility seems to be related to a person's capacity to produce IgE antibodies. Yet only 30 percent to 40 percent of people with allergic rhinitis have high IgE levels, and individuals with low IgE levels can still suffer from hay fever and other allergies.

In view of all the grief they cause, you have to wonder if IgE antibodies are good for anything. The answer may well be yes. Studies suggest that several kinds of human parasites provoke the formation of IgE antibodies and are rapidly destroyed by them. (These amoebas and worms are no longer common in this country, but they still cause serious health problems in underdeveloped parts of the world.) Looking at this intriguing discovery, a Swedish immunologist has speculated that "pollen allergy might partly be an undesirable consequence" of modern society's success in ridding itself of parasites and the diseases they cause.

Absence Makes The Nose Grow Fonder

Once hay fever has been diagnosed and the responsible allergen or allergens identified, the first line of defense is prevention — avoiding the pollen, house dust, mold spores, scales shed by the skins of animals (dander), or other substances that provoke an allergic reaction.

Sometimes this can be fairly easy. A patient may hate to part with a pet cat or give up horseback riding, but that may be all it takes to be free of symptoms. People allergic to mold spores may solve their problem by keeping out of damp, musty areas. They may also be well advised to avoid foods such as peanuts that may contain mold spores and not to take penicillin and similar drugs that can cause an allergic reaction in mold-sensitive people.

If house dust is the problem, frequent and thorough cleaning of the floors, fabrics such as carpets and curtains, upholstered furniture, and bedding can be beneficial. So can the use of high-efficiency indoor air-filtering devices (not those built into ordinary heating and air conditioning systems) that trap dust particles. (Filtering devices that really help don't come cheap. Beware of inexpensive — and ineffective — substitutes.) Persuasive evidence points to microscopic mites as the prime offenders in house dust allergies. While these spider-like creatures thrive during warm summer months, they may actually be more troublesome in colder weather when fragments of dead mites are more readily dispersed in the air and inhaled.

It is more difficult to avoid pollen and other outdoor airborne allergens. Air conditioning helps in homes, automobiles and workplaces. Simply keeping doors and windows closed can lower the allergen content of indoor air. Hay fever symptoms can be brought on by pollen concentrations as low as 20 grains per cubic meter of air; so during certain seasons, no outdoor area can be assumed pollen-free. Yet it is wise to be especially wary of areas known to have high concentrations of allergens. Another prudent measure for allergic rhinitis sufferers is to avoid irritants such as tobacco smoke, fumes, polluted air, and hair sprays.

It is seldom helpful to move someplace else to escape hay fever-causing pollen. Every part of the country has varieties of trees, weeds and grasses that shed allergenic pollen. People who try moving to the West Coast to escape ragweed pollen (ragweed does not grow in California, Oregon or Washington) may discover that they are allergic to a pollen found in the new location. Furthermore, pollen grains have been found in air samples collected as far as 400 miles at sea. The adage "you can run but you can't hide" is all too true for most hay fever sufferers.

About the Author

www.fda.gov
FDA is A United States government body that oversees medical devices, including contact lenses, intraocular lenses, excimer lasers and eyedrops. In the US, these products must be approved by the FDA before they can be marketed.