Allergies

Now let’s turn our attention to allergies. Unlike germs, the antigens are benign or not usually capable of causing a disease. Antigens such as pollens, which cause allergic reactions, are usually called allergens. Some allergens like pollens occur seasonally and result in episodic symptoms. Other allergens like dust-mites may be present year-round and cause perennial symptoms. An individual may be allergic to one or many substances. Allergens often cause allergies in genetically predisposed people.

A genetically predisposed person does not develop allergy symptoms the first time he is exposed to an allergen. The allergen is taken up by the antigen-presenting cells, chemically modified, and presented to B lymphocytes. For some reason, these B lymphocytes and plasma cells produce immunoglobulin E or IgE. IgE is the antibody class responsible for most allergic reactions. Once exposed, the person now has preformed IgE and is capable of experiencing allergic symptoms. The IgE molecules usually bind to the surface of 2 types of white blood cells: mast cells and basophils. Mast cells live in body tissues, while basophils circulate in blood.

Whenever the sensitized individual is exposed to the specific allergen, the specialized IgE binds to the allergen. The binding of an IgE to its allergen causes the mast cells and basophils to break apart, or degranulate. Mast cells and basophils contain many molecules capable of causing an immune response. Two of the most important are histamine and a class of chemicals called leukotrienes. Once in the tissues, histamine and leukotrienes cause blood flow to the tissue to increase. This results in congestion, such as tearing and a runny nose. White blood cells flood into the tissue, increasing the symptoms in a process called inflammation. Inflamed tissues are characterized by swelling, discomfort, redness, heat, and loss of function. The suffix -itis denotes inflammation. For example, rhinitis means an inflammed nose; conjunctivitis entails the inflammation of the white parts of the eyes; pharyngitis denotes an inflammed throat.

Allergies are not the only cause of inflammation. Germ-caused tissue inflammation often results in bright red, and painful tissues, as in a head cold or strep throat. Many other irritating substances can also inflame tissues. On the other hand, allergic inflammation is unique in that tissues may have a blue or purple hue, and may often be more itchy than painful. Recurrent exposure to an allergen results in greater tissue inflammation and more symptoms. Tissues with allergic inflammation contain a type of white blood cells called eosinophils, which can be viewed with a microscope.

Along with nasal congestion, many people with allergies experience problems with their ears and sinuses. The middle ears and sinuses are cavities or “rooms” within our heads. They connect to the nasal passages by small vents or openings. These vents are normally open and allow the middle ears and sinuses to be filled with air. Congestion caused by allergies (or any other substance) block the vents. At first, the sinuses and/or middle ears lose pressure. This can cause discomfort, blocked ears, and a vague sense of dizziness or disequilibrium. If the vents remain blocked, the sinuses and/or middle ears can fill up with fluid, called an effusion. If the vents remain blocked, the effusion can become infected. This results in sinusitis and/or otitis media. Antibiotics are often used to treat these secondary infections.

In addition to the above problems, the inflammation can cause fluid to drip down the back of the throat. This is called post-nasal drip (PND). PND causes people to clear their throat frequently and often causes a sore throat. Individuals with PND often do not sleep well and feel tired much of the time. Allergic rhinitis may also precipitate or worsen asthma.

Avoiding or minimizing exposure to allergens is critical. If a person with allergies never “sees” the allergen, they won’t react and develop symptoms. Although it is nearly impossible to completely avoid an allergen, steps can be taken to minimize exposure. For seasonal allergies, these include:

• Keeping windows closed at night and minimizing outdoor activities in the morning when pollen counts are high. Pollen counts tend to be very high on windy days.

• Using an air conditioner can also help reduce exposure to allergens.

• Try not to mow the lawn. If you must, consider wearing glasses and a mask.

• Do not hang your clothes out to dry. Allergens can collect on your laundry.

• If you have been outside and were exposed to allergens, consider changing your shirt and washing your face and hair with a wet cloth. If you have a pet that spends a lot of time outside, wipe the animal down too.

Indoor allergies are often caused by dust mites, molds, animal dander, and cockroaches. The control measures are specific to each type of allergen.

Dust Mites:

• Keep the relative humidity less than 50%.

• Minimize carpeting and curtains.

• Use specially designed covers for beds and pillows.

• Wash bed linens weekly in hot water and dry them with heat.

Molds:

• Keep the environment dry and use a dehumidifier if necessary.

• Use detergents to kill molds.

• Remove cloths, fabrics, and carpets filled with mold.

Animal dander:

• If possible, don’t get a pet that provokes your allergies.

• If you have a pet that causes your allergies, don’t allow the pet’s access to your bedroom.

• Eliminate carpets, which are filled with dander. Vacuuming is not usually an effective way to eliminate animal dander.

Cockroaches:

• Keep your house clean and dry.

• Store food in airtight containers.

• Exterminate cockroaches if necessary.

Many medicines are effective in managing allergies. These include decongestants, antihistamines, anti-inflammatory steroids, and drugs, which interfere with leukotrienes. Please note that the following information is not intended to be comprehensive; rather, it is designed to help familiarize you with possible options available to you. Individuals may have contraindications to one or more therapies. Please discuss your concerns with your healthcare professional.

Decongestants temporarily reduce tissue swelling. This can result in symptomatic relief. There are oral and intranasal preparations. Decongestants do not prevent or modify the allergic response. Regular use of intranasal decongestants may result in a chronically runny nose. Decongestants may be stimulating to may people and may worsen some cardiovascular conditions.

Antihistamines block histamine from binding to its targets and prevent much, but not all, of the allergic reaction. They need to be taken prior to allergen exposure. Antihistamines can be classified into two groups:
First generation (sedating) antihistamines, and second generation (non-sedating) antihistamines. Some first generation antihistamines are diphenhydramine (Benadryl) and chlorpheniramine (Chlor-Trimeton)—effective, but often sedating. Although generally considered safe, antihistamines may adversely affect some people with certain medical conditions (e.g., glaucoma, trouble urinating, certain heart conditions).

Second generation antihistamines work as well as first generation ones but tend to cause less sedation. They also usually work for longer periods of time, permitting once or twice daily dosing. Loratadine (Claritin), fexofenadine (Allegra), and cetirizine (Zyrtec) are examples. These drugs can cause side effects and have some toxicity. In addition, all antihistamines may interact with other drugs. Many antihistamines are combined with decongestants in one formulation. For example, Allegra D is fexofenadine combined with pseudoephedrine, a decongestant.

Topical antihistamines have been developed for use on the eyes and nose. Olopatadine (Patanol) may be applied to the eyes for allergic conjunctivitis; azelastine (Astenlin) is applied topically to the nose.

Anti-inflammatory steroids are a mainstay in the management of allergic rhinitis. These steroids suppress the “overactive” immune system and reduce tissue inflammation. They need to be used regularly for best results. While prolonged use of some anti-inflammatory steroids may result in serious toxicities (eg. osteoporosis, high blood pressure, adrenal suppression, increased susceptibility to infection, and decreased growth in children), intranasal steroid sprays are generally considered safe when used appropriately. The amount of steroid delivered by these sprays is small and not usually associated with toxicity. They may cause symptoms such as nasal irritation and/or nosebleeds in some people. Examples of nasal steroids include fluticasone (Flonase), budesonide (Rhinocort), triamcinolone (Nasacort), and mometasone (Nasonex).

Prior to the availability of intranasal steroids, systemic steroids were commonly used to treat allergies. Systemic steroids are occasionally used in severe cases but have generally been replaced by intranasal steroid sprays, which are safer.

Drugs active against leukotrienes work in one of two ways. They may interfere with the production of leukotrienes such as zileuton (Zyflo) or block or antagonize the actions of leukotrienes. Montelukast (Singulair) and zafirlukast (Accolate) are antagonists of leukotrienes. All of these drugs are effective in controlling asthma. Montelukast is approved for seasonal allergic rhinitis in children 2 years of age and older, as well as adults.

A class of therapy called mast cell stabilizers is also effective in controlling the allergic reaction. These drugs prevent mast cells from breaking apart after an allergen binds to IgE on its surface. They are modestly effective in controlling allergic reactions and need to be used regularly but are considered very safe. Cromolyn (Intal) and nedocromil (Tilade) are examples. Nedocromil may have some anti-inflammatory properties and may be more effective than cromolyn. However, cromolyn is available in a nasal spray for allergic rhinitis, whereas nedocromil is only available as an inhaler for use in asthma.

Since the above therapies target different aspects of the allergic process, they are often used in combinations.

Immunotherapy or desensitization may be effective in the management of allergies. This process is commonly known as getting allergy shots. Candidates for immunotherapy include patients whose symptoms are not well controlled through allergen avoidance and pharmacologic therapies. Patients are first tested to identify the allergen(s). The usual and most accurate method is through skin testing. Small amounts of the allergen in solution are placed on a small needle. The patient’s skin is pricked to introduce the allergen. An allergic person will quickly develop redness, itching, and a hive at the site. People do not react if they are not allergic to a specific allergen. The needles used in this process are very small and the discomfort is minor and brief. It is important to discontinue antihistamines in advance of testing, as their presence may blunt the allergic reaction. A person taking antihistamines may test “negative” even if he/she is truly allergic.

Some patients cannot undergo skin testing. They may have life-threatening reactions to allergens, or have skin diseases that preclude skin testing. These patients may have blood tested for the presence of IgE against specific allergens. This process is called radioallergosorbent testing, or RAST. If a person with symptoms typical of allergies has a positive RAST, they are probably allergic.

Allergy testing may be performed for other reasons. Most patients can be diagnosed with reasonable certainty based on their medical history and physical exam. Because patients may have similar symptoms due to non-allergic causes, allergy testing may be performed to help establish a diagnosis.

During immunotherapy, patients receive small injections containing the allergen(s) that cause their symptoms. The amount of allergen in solution is very small. Over many weeks, the concentration of allergen injected is gradually increased. Patient will receive the highest tolerable concentration of extract up to a certain maximum. They will then receive injections on a regular basis over a period a few years. Most patients will become less sensitive to the allergens and notice clinical improvement. They may be able to discontinue or reduce medication use. A smaller number of patients may become completely asymptomatic. Some people do not respond to a course of immunotherapy. Unfortunately, one cannot predict who will or won’t benefit from immunotherapy at this time. Risks to immunotherapy include local reactions at the injection site(s); a life-threatening reaction called anaphylaxis is the most severe form of reaction. Patients will be observed for a period of time after receiving an injection in case reactions occur.

Pregnant women who have been receiving immunotherapy may be able to continue this treatment. However, immunotherapy will not usually be started during pregnancy. The concentration of allergen in the extract will not usually be increased during pregnancy.

Biotechnology-produced therapies are now available for allergic disorders. Omalizumab (Xolair) is a monoclonal antibody that targets IgE. IgE that is bound to omalizumab will not participate in the allergic reaction. This therapy is currently indicated for the treatment of some patients with asthma. Clinical studies are being done to evaluate the potential role of omalizumab in the management of allergic rhinitis.

Some people have food allergies. Whenever a susceptible person consumes an allergen, the allergen will provoke an immune reaction in the stomach and intestines. These organs become inflamed and patients may develop abdominal pain, nausea, vomiting, cramps, and/or diarrhea. The manifestations of allergic gastroenteritis (inflamed stomach and intestines) are similar to infectious gastroenteritis, except allergies don’t usually cause a fever. Diagnosing food allergies can be difficult and requires elimination diets under controlled conditions. Since the management of allergies involves specific therapies, it is important to establish that one’s symptoms are due to an allergic reaction, and not due to some other process or intolerance. This principle can be applied to all allergic conditions. It should be noted that there are many other causes of intolerance to foods besides allergies.

Poison ivy is another form of a hypersensitivity reaction called a delayed hypersensitivity reaction. Whereas the allergies considered above occur immediately after exposure to an antigen, delayed hypersensitivity reactions develop hours or days after exposure to the antigen. These reactions involve cell-mediated immunity, differentiating them from IgE mediated allergic reactions such as allergic rhinitis.

What this means for you:

If you have nasal congestion, itchy eyes, and/or post-nasal drip, ask your health care professional if allergies may be the cause. If they are, try to determine the allergens responsible for your allergic reactions. This may require allergy testing. If you are allergic, ask your health-care professional:

How can I avoid exposure to the allergen(s)?
Are there any medicines I can take to minimize symptoms?