Atopy | |
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Other names | Atopic syndrome |
Eczema—a typical atopic manifestation | |
Pronunciation | |
Specialty | Dermatology, immunology |
Atopy is the tendency to produce an exaggerated immunoglobulin E (IgE) immune response to otherwise harmless substances in the environment. [2] Allergic diseases are clinical manifestations of such inappropriate, atopic responses. [2]
Atopy may have a hereditary component, although contact with the allergen or irritant must occur before the hypersensitivity reaction can develop (characteristically after re-exposure). [3] Maternal psychological trauma in utero may also be a strong indicator for development of atopy. [4]
The term atopy was coined by Arthur F. Coca and Robert Cooke in 1923. [5] [6] Many physicians and scientists use the term "atopy" for any IgE-mediated reaction (even those that are appropriate and proportional to the antigen), but many pediatricians reserve the word "atopy" for a genetically mediated predisposition to an excessive IgE reaction. [7] The term is from Greek ἀτοπία meaning "the state of being out of place", "absurdity". [8]
Atopic sensitization is considered in the case of a person having IgE positivity or a prick test positivity to any common food- or air-borne allergen. [9] Atopic conditions are considered: atopic dermatitis, allergic rhinitis (hay fever), allergic asthma, atopic keratoconjunctivitis. The likelihood of having asthma, rhinitis and atopic dermatitis together is 10 times higher than could be expected by chance. [10] Atopy is more common among individuals with a number of different conditions, such as eosinophilic esophagitis and non-celiac gluten sensitivity. [11] [12]
Allergic reactions can range from sneezing and rhinorrhoea to anaphylaxis and even death. [13]
In an allergic reaction, initial exposure to an otherwise harmless exogenous substance (known as an allergen) triggers the production of specific IgE antibodies by activated B cells. [13] These IgE antibodies bind to the surface of mast cells via high-affinity IgE receptors, a step that is not itself associated with a clinical response. [13] However, upon re-exposure, the allergen binds to membrane-bound IgE which activates the mast cells, releasing a variety of mediators. [13] This type I hypersensitivity reaction is the basis of the symptoms of allergic reactions, which range from sneezing and rhinorrhoea to anaphylaxis. [13] Allergens can be a number of different substances, for example pollen, dander, dust mites, and foods.
Atopic reactions are caused by localized hypersensitivity reactions to an allergen. Atopy appears to show a strong hereditary component. 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". [14] As well, maternal stress and perinatal programming is increasingly understood as a root cause of atopy, finding that "...trauma may be a particularly robust potentiator of the cascade of biological events that increase vulnerability to atopy and may help explain the increased risk found in low-income urban populations." [4]
Environmental factors are also thought to play a role in the development of atopy, and the 'hygiene hypothesis' is one of the models that may explain the steep rise in the incidence of atopic diseases, though this hypothesis is incomplete and in some cases, contradictory to findings. [4] 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 ("protective") elements and the allergic-response ("false alarm") elements within the immune system. [15]
Some studies also suggest that the maternal diet during pregnancy may be a causal factor in atopic diseases (including asthma) in offspring, suggesting that consumption of antioxidants, certain lipids, and/or a Mediterranean diet may help to prevent atopic diseases.
A Swedish research study titled "Atopy In Children Of Families With An Anthroposophic Lifestyle" comparing the rate of bronchial asthma, allergies, dermatitis, and other atopic diseases among Steiner school pupils and pupils in public schools originally appeared in the May 1, 1999, edition of the British medical journal The Lancet. The findings indicated that Steiner school pupils were "at a significantly lower risk of atopy" than children attending public schools. The researchers investigated a variety of factors in the lives of the Steiner school pupils that might have contributed to this lower rate of atopy, which included breastfeeding, reduced immunization, avoidance of antibiotics and medications that reduce fevers, consumption of bio-dynamic and organic foods, and other physical aspects of the children's lives. [16]
The multicenter PARSIFAL study in 2006, involving 6,630 children age 5 to 13 in 5 European countries, suggested that reduced use of antibiotics and antipyretics is associated with a reduced risk of allergic disease in children. [17]
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. [18] [19] Genes for atopy (C11orf30, STAT6, SLC25A46, HLA-DQB1, IL1RL1/IL18R1, TLR1/TLR6/TLR10, LPP, MYC/PVT1, IL2/ADAD1, HLA-B/MICA) [20] tend to be involved in allergic responses or other components of the immune system. The gene C11orf30 seems to be the most relevant for atopy as it may increase susceptibility to poly-sensitization. [21]
Bleach baths provide temporary control of eczema. [22] Ciprofloxacin is an allergen that may cause contact dermatitis, symptoms of which are indistinguishable from eczema. [23] Filaggrin 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. [24] 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. [25] 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. [26] 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 people with atopic eczema. [27] [28]
In adults, the prevalence of IgE sensitization to allergens from house dust mite and cat, but not grass, seems to decrease over time as people age. [29] However, the biological reasons for these changes are not fully understood.
Treatments for atopic disorders depend on the organ(s) involved. They can vary from local treatment options, often topical corticosteroids, to systemic treatment options with oral corticosteroids, biological treatments (e.g. omalizumab, mepolizumab) or allergen immunotherapy. [30] [31] [32]
Allergies, also known as allergic diseases, are various conditions caused by hypersensitivity of the immune system to typically harmless substances in the environment. These diseases include hay fever, food allergies, atopic dermatitis, allergic asthma, and anaphylaxis. Symptoms may include red eyes, an itchy rash, sneezing, coughing, a runny nose, shortness of breath, or swelling. Note that food intolerances and food poisoning are separate conditions.
Dermatitis is a term used for different types of skin inflammation, typically characterized by itchiness, redness and a rash. In cases of short duration, there may be small blisters, while in long-term cases the skin may become thickened. The area of skin involved can vary from small to covering the entire body. Dermatitis is also called eczema but the same term is often used for the most common type of skin inflammation, atopic dermatitis.
An allergen is an otherwise harmless substance that triggers an allergic reaction in sensitive individuals by stimulating an immune response.
Hypersensitivity is an abnormal physiological condition in which there is an undesirable and adverse immune response to an antigen. It is an abnormality in the immune system that causes immune diseases including allergies and autoimmunity. It is caused by many types of particles and substances from the external environment or from within the body that are recognized by the immune cells as antigens. The immune reactions are usually referred to as an over-reaction of the immune system and they are often damaging and uncomfortable.
Allergic rhinitis, of which the seasonal type is called hay fever, is a type of inflammation in the nose that occurs when the immune system overreacts to allergens in the air. It is classified as a type I hypersensitivity reaction. Signs and symptoms include a runny or stuffy nose, sneezing, red, itchy, and watery eyes, and swelling around the eyes. The fluid from the nose is usually clear. Symptom onset is often within minutes following allergen exposure, and can affect sleep and the ability to work or study. Some people may develop symptoms only during specific times of the year, often as a result of pollen exposure. Many people with allergic rhinitis also have asthma, allergic conjunctivitis, or atopic dermatitis.
Immunoglobulin E (IgE) is a type of antibody that has been found only in mammals. IgE is synthesised by plasma cells. Monomers of IgE consist of two heavy chains and two light chains, with the ε chain containing four Ig-like constant domains (Cε1–Cε4). IgE is thought to be an important part of the immune response against infection by certain parasitic worms, including Schistosoma mansoni, Trichinella spiralis, and Fasciola hepatica. IgE is also utilized during immune defense against certain protozoan parasites such as Plasmodium falciparum. IgE may have evolved as a defense to protect against venoms.
A food allergy is an abnormal immune response to food. The symptoms of the allergic reaction may range from mild to severe. They may include itchiness, swelling of the tongue, vomiting, diarrhea, hives, trouble breathing, or low blood pressure. This typically occurs within minutes to several hours of exposure. When the symptoms are severe, it is known as anaphylaxis. A food intolerance and food poisoning are separate conditions, not due to an immune response.
Latex allergy is a medical term encompassing a range of allergic reactions to the proteins present in natural rubber latex. It generally develops after repeated exposure to products containing natural rubber latex. When latex-containing medical devices or supplies come in contact with mucous membranes, the membranes may absorb latex proteins. In some susceptible people, the immune system produces antibodies that react immunologically with these antigenic proteins. Many items contain or are made from natural rubber, including shoe soles, pen grips, hot water bottles, elastic bands, rubber gloves, condoms, baby-bottle nipples, and balloons; consequently, there are many possible routes of exposure that may trigger a reaction. People with latex allergies may also have or develop allergic reactions to some fruits, such as bananas.
Type I hypersensitivity, in the Gell and Coombs classification of allergic reactions, is an allergic reaction provoked by re-exposure to a specific type of antigen referred to as an allergen. Type I is distinct from type II, type III and type IV hypersensitivities. The relevance of the Gell and Coombs classification of allergic reactions has been questioned in the modern-day understanding of allergy, and it has limited utility in clinical practice.
Allergic conjunctivitis (AC) is inflammation of the conjunctiva due to allergy. Although allergens differ among patients, the most common cause is hay fever. Symptoms consist of redness, edema (swelling) of the conjunctiva, itching, and increased lacrimation. If this is combined with rhinitis, the condition is termed allergic rhinoconjunctivitis (ARC).
Atopic dermatitis (AD), also known as atopic eczema, is a long-term type of inflammation of the skin. AD is also often called simply eczema but the same term is also used to refer to dermatitis, the larger group of skin conditions. AD results in itchy, red, swollen, and cracked skin. Clear fluid may come from the affected areas, which can thicken over time.
Milk allergy is an adverse immune reaction to one or more proteins in cow's milk. Symptoms may take hours to days to manifest, with symptoms including atopic dermatitis, inflammation of the esophagus, enteropathy involving the small intestine and proctocolitis involving the rectum and colon. However, rapid anaphylaxis is possible, a potentially life-threatening condition that requires treatment with epinephrine, among other measures.
Egg allergy is an immune hypersensitivity to proteins found in chicken eggs, and possibly goose, duck, or turkey eggs. Symptoms can be either rapid or gradual in onset. The latter can take hours to days to appear. The former may include anaphylaxis, a potentially life-threatening condition which requires treatment with epinephrine. Other presentations may include atopic dermatitis or inflammation of the esophagus.
Allergic inflammation is an important pathophysiological feature of several disabilities or medical conditions including allergic asthma, atopic dermatitis, allergic rhinitis and several ocular allergic diseases. Allergic reactions may generally be divided into two components; the early phase reaction, and the late phase reaction. While the contribution to the development of symptoms from each of the phases varies greatly between diseases, both are usually present and provide us a framework for understanding allergic disease.
Wheat allergy is an allergy to wheat that typically presents itself as a food allergy, but can also be a contact allergy resulting from occupational exposure. Like all allergies, wheat allergy involves immunoglobulin E and mast cell response. Typically, the allergy is limited to the seed storage proteins of wheat. Some reactions are restricted to wheat proteins, while others can occur across many varieties of seeds and other plant tissues. Wheat allergy is rare. Prevalence in adults was estimated to be 0.21% in a 2012 study in Japan.
Oat sensitivity represents a sensitivity to the proteins found in oats, Avena sativa. Sensitivity to oats can manifest as a result of allergy to oat seed storage proteins either inhaled or ingested. A more complex condition affects individuals who have gluten-sensitive enteropathy in which there is an autoimmune response to avenin, the glutinous protein in oats similar to the gluten within wheat. Sensitivity to oat foods can also result from their frequent contamination by wheat, barley, or rye particles.
Fish allergy is an immune hypersensitivity to proteins found in fish. Symptoms can be either rapid or gradual in onset. The latter can take hours to days to appear. The former may include anaphylaxis, a potentially life-threatening condition which requires treatment with epinephrine. Other presentations may include atopic dermatitis or inflammation of the esophagus. Fish is one of the eight common food allergens which are responsible for 90% of allergic reactions to foods: cow's milk, eggs, wheat, shellfish, peanuts, tree nuts, fish, and soy beans.
Shellfish allergy is among the most common food allergies. "Shellfish" is a colloquial and fisheries term for aquatic invertebrates used as food, including various species of molluscs such as clams, mussels, oysters and scallops, crustaceans such as shrimp, lobsters and crabs, and cephalopods such as squid and octopus. Shellfish allergy is an immune hypersensitivity to proteins found in shellfish. Symptoms can be either rapid or gradual in onset. The latter can take hours to days to appear. The former may include anaphylaxis, a potentially life-threatening condition which requires treatment with epinephrine. Other presentations may include atopic dermatitis or inflammation of the esophagus. Shellfish is one of the eight common food allergens, responsible for 90% of allergic reactions to foods: cow's milk, eggs, wheat, shellfish, peanuts, tree nuts, fish, and soy beans.
The allergic march is a medical term used to explain the natural history of atopic manifestations. The allergic march is characterized by some antibody responses to immunoglobulin E (IgE) and clinical symptoms that may appear in childhood, and continue for years or decades and often changing with age. The atopic march is a term that describes the progression of atopic disorders, from eczema in young infants and toddlers to allergic rhinitis and finally to asthma in adulthood. Symptoms include atopic dermatitis, food allergy, allergic rhinitis and asthma.
A food allergy to sesame seeds has prevalence estimates in the range of 0.1–0.2% of the general population, and are higher in the Middle East and other countries where sesame seeds are used in traditional foods. Reporting of sesame seed allergy has increased in the 21st century, either due to a true increase from exposure to more sesame foods or due to an increase in awareness. Increasing sesame allergy rates have induced more countries to regulate food labels to identify sesame ingredients in products and the potential for allergy. In the United States, sesame became the ninth food allergen with mandatory labeling, effective 1 January 2023.
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