Home      Discussion      Topics      Dictionary      Almanac
Signup       Login
Atopy

Atopy

Discussion
Ask a question about 'Atopy'
Start a new discussion about 'Atopy'
Answer questions from other users
Full Discussion Forum
 
Encyclopedia
Atopy or atopic syndrome is a predisposition toward developing certain allergic hypersensitivity
Hypersensitivity
Hypersensitivity refers to undesirable reactions produced by the normal immune system, including allergies and autoimmunity. These reactions may be damaging, uncomfortable, or occasionally fatal. Hypersensitivity reactions require a pre-sensitized state of the host. The four-group classification...

 reactions.
Atopy may have a hereditary
Heredity
Heredity is the passing of traits to offspring . This is the process by which an offspring cell or organism acquires or becomes predisposed to the characteristics of its parent cell or organism. Through heredity, variations exhibited by individuals can accumulate and cause some species to evolve...

 component, although contact with the allergen
Allergen
An allergen is any substance that can cause an allergy. In technical terms, an allergen is a non-parasitic antigen capable of stimulating a type-I hypersensitivity reaction in atopic individuals....

 must occur before the hypersensitivity reaction can develop .

The term "atopy" was coined by Coca and Cooke in 1923. Many physicians and scientists use the term "atopy" for any IgE
IGE
IGE was one of the largest services company buying and selling virtual currencies and accounts for MMORPG. During its peak time, it had offices in Los Angeles, China , and headquarters & customer service centre in Hong Kong. IGE was one of the main monopoly in virtual economy services, also known...

-mediated reaction (even those appropriate and proportional), but many pediatricians reserve the word "atopy" for a genetically mediated predisposition to an excessive IgE reaction.

Signs and symptoms


Atopy (atopic syndrome) is a syndrome characterized by a tendency to be “hyperallergic”. A person with atopy typically presents with one or more of the following: eczema
Eczema
Eczema is a form of dermatitis, or inflammation of the epidermis . In England, an estimated 5.7 million or about one in every nine people have been diagnosed with the disease by a clinician at some point in their lives.The term eczema is broadly applied to a range of persistent skin conditions...

 (atopic dermatitis
Atopic dermatitis
Atopic dermatitis is an inflammatory, chronically relapsing, non-contagious and pruritic skin disorder...

), allergic rhinitis
Allergic rhinitis
Allergic rhinitis, also known as pollenosis or hay fever, is an allergic inflammation of the nasal airways.It occurs when an allergen, such as pollen, dust or animal dander is inhaled by an individual with a sensitized immune system...

 (hayfever), allergic conjunctivitis
Allergic conjunctivitis
Allergic conjunctivitis is inflammation of the conjunctiva due to allergy. Although allergens differ between patients, the most common cause is hay fever. Symptoms consist of redness , oedema of the conjunctiva, itching and increased lacrimation...

, or allergic asthma. Patients with atopy also have a tendency to have food allergies.

Patients with atopy usually develop what is referred to as the “allergic triad” of symptoms, i.e., eczema (atopic dermatitis), hayfever (allergic rhinitis), and allergy-induced asthma (allergic asthma). They also have a tendency to have food allergies, and other symptoms characterized by their hyperallergic state. For example, eosinophilic esophagitis
Eosinophilic esophagitis
Eosinophilic esophagitis is an allergic inflammatory condition of the esophagus. Symptoms are swallowing difficulty, food impaction, and heartburn. The disease was first described in children but occurs in adults as well...

 is found associated with atopic allergies.

Atopic syndrome can be fatal for those that experience serious allergic reactions, such as anaphylaxis
Anaphylaxis
Anaphylaxis is defined as "a serious allergic reaction that is rapid in onset and may cause death". It typically results in a number of symptoms including throat swelling, an itchy rash, and low blood pressure...

, brought on by reactions to food or environment.

Pathophysiology


The individual components of atopy are all caused at least in part by allergy
Allergy
An Allergy is a hypersensitivity disorder of the immune system. Allergic reactions occur when a person's immune system reacts to normally harmless substances in the environment. A substance that causes a reaction is called an allergen. These reactions are acquired, predictable, and rapid...

 (type I hypersensitivity reactions). Therefore, atopic responses appear after the body is exposed to various allergens, for example pollen
Pollen
Pollen is a fine to coarse powder containing the microgametophytes of seed plants, which produce the male gametes . Pollen grains have a hard coat that protects the sperm cells during the process of their movement from the stamens to the pistil of flowering plants or from the male cone to the...

, dander
Dander
Dander is an informal term for a material shed from the body of various animals, similar to dandruff. It may contain scales of dried skin and hair, or feathers. It is a cause of allergies in humans....

, dust mites, certain foods, or chemical/physical irritants.

Although atopy has various definitions, in general, it is defined by the presence of elevated levels of total and allergen-specific IgE
IGE
IGE was one of the largest services company buying and selling virtual currencies and accounts for MMORPG. During its peak time, it had offices in Los Angeles, China , and headquarters & customer service centre in Hong Kong. IGE was one of the main monopoly in virtual economy services, also known...

 in the serum
Blood plasma
Blood plasma is the straw-colored liquid component of blood in which the blood cells in whole blood are normally suspended. It makes up about 55% of the total blood volume. It is the intravascular fluid part of extracellular fluid...

, leading to positive skin-prick tests to common allergens.

Causes


Atopic reactions are caused by localized hypersensitivity reaction to an allergen. Atopy appears to show a strong hereditary component
Genetic disorder
A genetic disorder is an illness caused by abnormalities in genes or chromosomes, especially a condition that is present from before birth. Most genetic disorders are quite rare and affect one person in every several thousands or millions....

. One study concludes that the risk of developing atopic dermatitis (3%) or atopy in general (7%) "increases by a factor of two with each first-degree family member already suffering from atopy".

Environmental factors are also thought to play a role in the development of atopy, and the 'hygiene hypothesis' is one of the paradigms available to date that may explain the steep rise in the incidence of atopic diseases. This hypothesis proposes that excess 'cleanliness' in an infant's or child's environment can lead to a decline in the number of infectious stimuli that are necessary for the proper development of the immune system. The decrease in exposure to infectious stimuli may result in an imbalance between the infectious-response elements and the allergic-response elements within the immune system.

Some studies also suggest that the maternal diet during pregnancy may be a causal factor in atopic diseases (including asthma) in offspring, suggesting antioxidants, certain lipids, and a Mediterranean diet may help to prevent atopic diseases.

The multicenter PARSIFAL study
PARSIFAL study
PARSIFAL was a 2006 multicenter study, conducted in five European countries, comparing the incidence of atopic disease in children attending Steiner schools with that in children attending other schools...

 in 2006, involving 6630 children age 5 to 13 in 5 European countries, suggested that restrictive use of antibiotic
Antibiotic
An antibacterial is a compound or substance that kills or slows down the growth of bacteria.The term is often used synonymously with the term antibiotic; today, however, with increased knowledge of the causative agents of various infectious diseases, antibiotic has come to denote a broader range of...

s and antipyretic
Antipyretic
Antipyretics ; an-tee-pahy-ret-iks; from the Greek anti, against, and pyreticus, are drugs or herbs that reduce fever. Normally, they will not lower body temperature if one does not have a fever. Antipyretics cause the hypothalamus to override an interleukin-induced increase in temperature...

s are associated with a reduced risk of allergic disease in children.

Genetics


There is a strong genetic predisposition toward atopic allergies, especially on the maternal side. Because of the strong familial evidence, investigators have tried to map susceptibility genes for atopy. These have been reviewed, but, in essence, genes for atopy tend to be involved in allergic responses or other components of the immune system.

Staphylococcus aureus colonization


Patients with atopic eczema often improve with the administration of antibiotics or bleach baths (half a cup of bleach per tubful of water) to control bacterial colonization on the skin. Filaggrin
Filaggrin
Filaggrin is a filament-associated protein that binds to keratin fibers in epithelial cells.-Profilaggrin:Filaggrin monomers are tandemly clustered into a large, 350kDa protein precursor known as profilaggrin. In the epidermis, these structures are present in the keratohyalin granules in cells of...

mutations are associated with atopic eczema, and may contribute to the excessive dryness of the skin and the loss of the barrier function of normal skin. It may be possible that the filaggrin mutations and the loss of the normal skin barrier expose crevices that make it possible for Staphylococcus aureus to colonize the skin. Atopic eczema is often associated with genetic defects in genes that control allergic responses. Thus, some investigators have proposed that atopic eczema is an allergic response to increased Staphylococcus aureus colonization of the skin. A hallmark indicator of atopic eczema is a positive “wheal-and-flare” reaction to a skin test of S. Aureus antigens. In addition, several studies have documented that an IgE-mediated response to S. aureus is present in patients with atopic eczema. The unmistakable improvement in atopic eczema observed with antibiotic administration or bleach baths helps correlate the hypothesis that Staphylococcus aureus colonization is critical to the appearance of atopic eczema.

Treatments


Corticosteroids: For years, there was no treatment for atopic eczema. Atopy was believed to be allergic in origin due to the patients’ extremely high serum IgE levels, but standard therapies at the time did not help. Oral prednisone was sometimes prescribed for severe cases. Wet wraps (covering the patients with gauze like a mummy) were sometimes used in hospitals to control itching. However, a true medical miracle occurred in the 1950s with the discovery that corticosteroids could be used topically in creams or ointments for atopic eczema and other conditions. Thus, the use of topical steroids avoided many of the undesirable side-effects of systemic administration of corticosteroids. Topical steroids control the itching and the rash that accompanies atopic eczema. Side-effects of topical steroid use are plentiful, and the patient is advised to use topical steroids in moderation and only as needed.

Immune modulators: Pimecrolimus and tacrolimus creams and ointments became available in the 1980s, and are sometimes prescribed for atopic eczema. They act by interfering with T cells, but have been linked to the development of cancer.

Avoiding dry skin: Dry skin is a common feature of patients with atopic eczema (see also eczema for information), and can exacerbate atopic eczema.

Avoiding allergens and irritants: See eczema for information.

External links