Allergies and the Immune System Allergy involves a response of the immune system, often to common substances. ( courtecy;- medicineNet.com
Allergy (Allergies)
Allergy facts
- Allergy involves an exaggerated response of the immune system, often to common substances such as foods or pollen.
- The immune system is a complex system that normally defends the body against foreign invaders, such as bacteria and viruses, while also surveying for abnormal changes in an individual’s own cells, such as cancer.
- Allergens are substances that are foreign to the body and that cause an allergic reaction.
- IgE is the allergic antibody.
- Although many individuals outgrow allergies over time, allergies can also develop at any age, including during adulthood.
- While the environment plays a role in the development of allergy, there is a greater risk of developing allergic conditions if a person has a family history of allergy, especially in parents or siblings.
Allergy overview
This is a review regarding how the allergic response of the immune system occurs and why certain people become allergic. The most common allergic diseases are described, including allergic rhinitis (nasal allergies), allergic conjunctivitis (eye allergies), allergic asthma, urticaria (hives), and food allergies.
What is an allergy?
An allergy refers to an exaggerated reaction by the immune system in response to exposure to certain foreign substances. The response is exaggerated because these foreign substances are normally seen by the body as harmless in nonallergic individuals and do not cause a response in them. In allergic individuals, the body recognizes the foreign substance, and the allergic part of the immune system generates a response.
Allergy-producing substances are called "allergens." Examples of allergens include pollens, dust mites, molds, animal proteins, foods, and medications. When an allergic individual comes in contact with an allergen, the immune system mounts a response through the IgE antibody. People who are prone to allergies are said to be allergic or "atopic."
Peanut Allergy Symptoms and Signs
Types of peanut allergy symptoms: About 80%-90% of reactions involve skin manifestations such as
- a rash, including hives,
- redness,
- itching.
Nevertheless, reactions can occur in the absence of a rash, and these reactions may be the most severe.
What is an allergy? (Continued)
Allergy prevalence:
- Approximately 10%-30% of individuals in the industrialized world are affected by allergic conditions, and this number is increasing.
- Allergic rhinitis (nasal allergies) affects roughly 20% of Americans. Between prescription costs, physician visits, and missed days of work/school, the economic burden of allergic disease exceeds $3 billion annually.
- Asthma affects roughly 8%-10% of Americans. The estimated health costs for asthma exceed approximately $20 billion annually.
- Food allergies affect roughly 3%-6% of children in the United States, and roughly 1%-2% of adults in the U.S.
- The prevalence of allergic conditions has increased significantly over the last two decades and continues to rise.
What causes allergies?
A common scenario can help explain how allergies develop. A few months after the new cat arrives in the house, dad begins to have itchy eyes and episodes of sneezing. One of the three children develops coughing and wheezing. The mom and the other two children experience no reaction whatsoever despite the presence of the cat. How can this occur?
The immune system is the body's organized defense mechanism against foreign invaders, particularly infections. Its job is to recognize and react to these foreign substances, which are called antigens. Antigens often lead to an immune response through the production of antibodies, which are protective proteins that are specifically targeted against particular antigens. These antibodies, or immunoglobulins (IgG, IgM, and IgA), are protective and help destroy a foreign particle by attaching to its surface, thereby making it easier for other immune cells to destroy it. The allergic person however, develops a specific type of antibody called immunoglobulin E, or IgE, in response to certain normally harmless foreign substances, such as cat dander. Other antigens, such as bacteria, do not lead to production of IgE, and therefore do not cause allergic reactions. Once IgE is formed, it can recognize the antigen, such as cat dander, and can then trigger an allergic response. IgE was discovered and named in 1967 by Kimishige and Teriko Ishizaka.
What causes allergies? (Continued)
In the pet cat example, the dad and the youngest daughter developed IgE antibodies in large amounts that were targeted against the cat allergen. The dad and daughter are now sensitized or prone to develop allergic reactions on repeated exposures to cat allergen. Typically, there is a period of "sensitization" ranging from days to years prior to an allergic response. Although it might occasionally appear that an allergic reaction has occurred on the first exposure to the allergen, there needs to be prior exposure in order for the immune system to react. It is important to realize that it is impossible to be allergic to something that an individual has truly never been exposed to before, though the first exposure may be subtle or unknown. The first exposure can even occur in a baby in the womb, through breast milk, or through the skin.
IgE is an antibody that all of us have in small amounts. Allergic individuals, however, generally produce IgE in larger quantities. Historically, this antibody was important in protecting us from parasites. In the example above, during a sensitization period, cat dander IgE is overproduced and coats other cells involved in the allergic response, such as mast cells and basophils, which contain various mediators, such as histamine. These cells are capable of leading to an allergic reaction on subsequent exposures to the cat allergen (cat dander). The cat protein is recognized by the IgE, leading to activation of the cells, which leads to the release of the allergic mediators mentioned above. These chemicals cause typical allergic symptoms, such as localized swelling, inflammation, itching, and mucus production. Once primed, or sensitized, the immune system is capable of mounting this exaggerated response with subsequent exposures to the allergen.
On exposure to cat dander, whereas the dad and daughter produce IgE, the mom and the other two children produce other classes of antibodies, which do not cause allergic reactions. In these nonallergic members of the family, the cat protein is eliminated uneventfully by the immune system and the cat has no effect on them.
Another part of the immune system, the T-cell, may be involved in allergic responses in the skin, as occurs from the oils of plants, such as poison ivy, poison oak, poison sumac, reactions to metal, such as nickel, or certain chemicals. The T-cell may recognize a certain allergen in a substance contacting the skin and cause an inflammatory response. This inflammatory response can cause itching, rash, and discomfort.
Who is at risk for allergies and why?
Allergies can develop at any age, but most food allergies begin at a young age, and many are outgrown. Environmental allergies can develop at any time. The initial exposure or sensitization period may even begin before birth. Individuals can also outgrow allergies over time. It is not fully understood why one person develops allergies and another does not, but there are several risk factors for allergic conditions. Family history, or genetics, plays a large role, with a higher risk for allergies if parents or siblings have allergies. There are numerous other risk factors for developing allergic conditions. Children born via Cesarean section have a higher risk of allergy as compared to children who are delivered vaginally. Exposure to tobacco smoke and air pollution increases the risk of allergy. Boys are more likely to be allergic than girls. Allergies are more common in westernized countries, and less common in those with a farming lifestyle. Exposures to antigens, use of antibiotics, and numerous other factors, some of which are not yet known, also contribute to the development of allergies. This complicated process continues to be an area of medical research.
What are common types of allergic conditions, and what are allergy symptoms and signs?
The parts of the body that are prone to allergic symptoms include the eyes, nose, lungs, skin, and gastrointestinal tract. Although the various allergic diseases may appear different, they all result from an exaggerated immune response to foreign substances in sensitive individuals. The following are brief descriptions of common allergic disorders.
Allergic rhinitis (hay fever)
Allergic rhinitis ("hay fever") is the most common of the allergic diseases and refers to nasal symptoms that are due to aeroallergens. Year-round, or perennial, allergic rhinitis is usually caused by indoor allergens, such as dust mites, animal dander, or molds. Seasonal allergic rhinitis is typically caused by tree, grass, or weed pollens. Many individuals have a combination of both seasonal and perennial allergies. Symptoms result from the inflammation of the tissues that line the inside of the nose after exposure to allergens. The eyes, ears, sinuses, and throat can also be involved. The most common symptoms include the following:
- Runny nose
- Stuffy nose
- Sneezing
- Itchy nose, eyes, ears, and throat
- Postnasal drip (throat clearing)
মন্তব্যসমূহ
একটি মন্তব্য পোস্ট করুন