Close-up on allergies: Immune system fights foreign particles

It’s summertime, and for many people with allergies, that means an itchy nose, watery eyes, sneezing, and congestion that aren’t problems during other seasons.

An allergy is an abnormal immune system response to a substance that would otherwise be harmless to the body. People can be allergic to almost anything to which the body is exposed, from food and medications to pets and household chemicals.

Hay fever, or seasonal rhinitis, is one of the most common seasonal allergies.

Hay fever is an allergic response to pollen particles in the air. Part of the reason that people with hay fever experience watery eyes and sneezing during the summer is that pollen is more common in the summer air.

Ragweed pollen, for instance, can be found in air samples 2 miles out to sea and 400 feet high in the air, according to the National Institute of Allergy and Infectious Diseases (NIAID).

Also, people can be allergic to many different kinds of pollen, which is why some people suffer seasonal rhinitis at different times of year.

The allergic response occurs when the body’s immune system accidentally interprets a harmless substance as a threat to the body. It begins when B cells in the body’s immune system encounter a particular substance and respond by creating antibodies against that substance.

Antibodies are large, Y-shaped proteins that can fight infection by recognizing a certain foreign molecule, similarly to how a lock fits into a key. Once antibodies have been formed for a molecule — now called an antigen — the body can recognize that molecule forever. Antigens that cause allergic responses are called allergens.

The antibodies produced by the B cells move through the blood stream and attach to the surface of two kinds of immune cells: mast cells and basophils. Mast cells are found in connective tissue all over the body, and basophils circulate in the blood stream.

Both types of cells play an important role in the inflammatory response, which is one of the ways the body protects itself against invading pathogens and foreign molecules. Unfortunately, this response can also be triggered during an allergic reaction to a harmless substance.

Mast cells and basophils contain pockets of immune-mediating chemicals, such as histamine, that act in the body to produce an inflammatory response. As soon as the antibodies on these cells recognize the antigen, the cells release these chemicals into the blood stream and surrounding tissue.

Once released, these chemicals cause a person’s allergic response, which typically includes a runny nose, itchy eyes and throat, and congestion. Allergic responses can also include hives (itchy red bumps or welts) on the skin, nausea, and vomiting (in food allergies).

In some people, certain antigens can cause severe systemic reactions, including swelling of appendages, sudden drops in blood pressure, and constriction of the airways. This allergic condition is called anaphylaxis, or anaphylactic shock. Anaphylaxis is a life-threatening condition and requires immediate medical attention.

There are a number of treatments for allergies. Avoiding the allergen is always the best way to prevent a reaction, but avoidance is not always possible.

In the case of mild reactions, such as hay fever, an antihistamine can be taken. Antihistamines block histamine’s ability to cause unpleasant symptoms of allergies.

Over-the-counter antihistamines such as Benadryl can be taken for short-term allergies, such as mosquito bites, but they should not be taken long-term because they can cause drowsiness.

Prescription antihistamines such as Claritin and Allegra, on the other hand, don’t cause drowsiness and can be taken for longer time periods.

In addition, people with severe allergies may benefit from immunotherapy. Immunotherapy consists of a series of allergy shots containing dilute concentrations of the allergen, given over a period of time from a few months to a few years. This treatment desensitizes the body and can cause allergy symptoms to decrease or even disappear.

Incidence of allergic reaction has been increasing all over the world. The American Academy of Allergy, Asthma & Immunology estimates that 40 to 50 million Americans have allergies of some form.

Of particular concern to the health care community has been the steady rise of food allergies, which can be life-threatening. According to a 2006 article in the Journal of the European Molecular Biology Consortium, the number of hospital admissions for food allergies has increased 500 percent in the U.K. since 1990.

The rise in food allergies seems to be due in part to greater use of certain kinds of allergy-inducing foods. This is exemplified by increasing use of peanuts by the food industry, which has been correlated with increasing allergy rates.

On the other hand, according to a 2006 article in The Boston Globe, a recent study found that peanut allergies are much less prevalent in countries where children are fed a diet heavy in peanuts. This indicates that feeding children peanuts may actually protect them from developing an allergy to them.

In fact, early exposure to an environmental toxin may be a protective factor in many kinds of allergies. For example, according to a recent NIAID-funded research study, children who are exposed to household pets in the first years of life are much less likely to develop allergies of all kinds.

There are multiple factors that may be involved in the onset of allergies. According to the National Jewish Medical and Research Center, developing an allergy likely involves genetic, environmental, and immune system factors.