Atopy

Overview

Atopy is characterized by an excessive immunoglobulin E (IgE) immunological response to apparently innocuous environmental substances. Allergic disorders are clinical symptoms of such atypical, atopic reactions.

When having atopy, the immune system is more susceptible to typical allergy triggers that the individuals have inhaled or ingested. As a result, those who are impacted have a stronger-than-normal sensitivity to allergens such as dust, pollen, peanuts, or shellfish.

Atopy may be inherited, however contact with the allergen or irritant must occur before the hypersensitivity reaction may begin (characteristically after re-exposure). In utero maternal psychological stress may also be a powerful predictor of atopy development.

Atopy is thought to be caused by a number of genes, according to researchers. Around 80% of persons with atopy have other family members who suffer from allergy disorders.

Atopic sensitization is established as IgE or prick test positive to any common food or airborne allergen. Atopic dermatitis, allergic rhinitis (hay fever), allergic asthma, and atopic keratoconjunctivitis are all examined.

The chances of having asthma, rhinitis, and atopic dermatitis all at the same time are ten times higher than would be anticipated by chance. Atopy is more frequent in people with a variety of disorders, including eosinophilic esophagitis and non-celiac gluten sensitivity. Allergic responses can vary from sneezing and rhinorrhoea to anaphylaxis and, in extreme cases, death. 

 

Epidemiology of Atopic disorders

Atopy affects a considerable proportion of the general population, with estimates ranging from 10% to 30% in developed nations. Approximately 80% of atopic people have a family history of allergy, compared to approximately 20% of the general population. There is barely 50% concordance among monozygotic twins. Atopic disorders susceptibility is inherited, however rather than one or two causal dominant genes, evidence shows that several genes with modest effects are involved.

Allergic rhinitis affects 10% to 12% of the population in the United States. The geographic distribution of common allergens, such as dust mites and allergic plants, contributes to the prevalence and morbidity rate. Both sexes are impacted equally. 

Bronchial asthma is prevalent in many parts of the world. It is a prevalent illness that affects 5% of the Western world's population. It kills about 3000 people in the United States each year. Despite significant advancements in immunotherapy, death and morbidity rates continue to rise. In 2014, there were 8.4 million asthmatic children in the United States, with 11.1% living in impoverished metropolitan areas.

 

How is Atopy developed?

An allergic response occurs when an otherwise innocuous foreign material (known as an allergen) causes activated B cells to produce particular IgE antibodies. These IgE antibodies attach to the surface of mast cells through high-affinity IgE receptors, which is not linked with a clinical response.

When exposed again, the allergen attaches to membrane-bound IgE, activating mast cells and releasing a range of mediators. This type I hypersensitivity reaction is at the root of allergy symptoms ranging from sneezing and rhinorrhea to anaphylaxis. Allergens can be a variety of items such as pollen, dander, dust mites, and foods.

Basophils and mast cell mediators contain biogenic amines and enzymes stored premade in granules, as well as cytokines and lipid mediators, which are mostly generated upon cell activation. Histamine and other biogenic amines, as well as lipid mediators, cause vascular leakage and intestinal hypermotility, all of which are components of acute allergic reactions. 

Cytokines and lipid mediators contribute to the inflammation that occurs as part of a late-phase response. Enzymes are thought to contribute to tissue injury. Activated eosinophils produce enzymes and cationic proteins that are harmful to both parasites and host cells. Some eosinophil granule enzymes are thought to be involved in tissue damage in chronic allergic diseases.

A proposed cause for allergic dermatitis is faulty lymphocyte control. Defective results have been recorded for delayed hypersensitivity skin test responses to allergens, in vitro lymphocyte responses to mitogens or allergens, and autologous mixed lymphocyte reactions. 

It has been shown that an increased vulnerability to vaccinia virus, molluscum contagiosum, warts, herpes simplex virus, and dermatophyte skin diseases is associated with a deficiency in the T lymphocyte effector pathway in atopic dermatitis. There is some suspicion that an abnormal or dysfunctional CD4+ helper T cell population might explain why CD8+ T cells fail to serve as immunosuppressors of IgE synthesis.

 

What are the histopathologic features of Atopy?

Atopy manifests as a histopathologically distinct wheal and flare reaction in the skin, which is caused by an allergen-stimulated release of mediators from mast cells, local blood vessels that inflate and become leaky to proteins and fluids, resulting in local swelling and redness.

Bronchial asthma histology reveals a sick bronchus with increased mucus production, many submucosal inflammatory cells, including lymphocytes and eosinophils, thicker basement membrane, and smooth muscle hypertrophy. 

 

Causes of Atopy

Localized hypersensitivity responses to an allergen create atopic reactions. Atopy appears to have a major genetic component. According to one research, the chance of having atopic dermatitis (3%) or atopy in general (7%) "increases by a factor of two for each first-degree family member who already has atopy." 

Furthermore, maternal stress and perinatal programming are becoming more recognized as a root cause of atopy, with researchers discovering 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."

Environmental variables are assumed to have a role in the development of atopy, and the 'hygiene hypothesis' is one of the theories that may explain the sharp rise in the occurrence of atopic disorders, albeit this concept is inadequate and, in some cases, contradictory to findings. This theory claims that excessive 'cleanliness' in an infant's or child's surroundings might lead to a decrease in the number of infectious stimuli required for optimal immune system development. Reduced exposure to viral stimuli may cause an imbalance in the immune system's infectious-response ("protective") and allergic-response ("false alarm") components.

Some studies also show that the maternal diet during pregnancy may be a causative role in the development of atopic disorders (including asthma) in offspring, implying that intake of antioxidants, certain lipids, and/or a Mediterranean diet may assist to avoid atopic diseases. 

• Genetics

Atopic allergies have a substantial hereditary propensity, particularly on the maternal side. Because of the significant family evidence, researchers have attempted to map atopy susceptibility genes. Atopy genes (C11orf30, STAT6, SLC25A46, HLA-DQB1, IL1RL1/IL18R1, TLR1/TLR6/TLR10, LPP, MYC/PVT1, IL2/ADAD1, HLA-B/MICA) are known to be involved in allergy reactions or other immune system components. C11orf30 appears to be the most important for atopy, since it may enhance vulnerability to poly-sensitization.

• Staphylococcus aureus infection

Eczema can be temporarily controlled with bleach baths. Ciprofloxacin is an allergen that can induce contact dermatitis, which has symptoms similar to eczema. Filaggrin mutations are linked to atopic eczema and may contribute to excessive skin dryness and the loss of normal skin's barrier function. It is conceivable that the filaggrin mutations and lack of the normal skin barrier reveal fissures that allow Staphylococcus aureus to invade the skin.

Atopic eczema is frequently linked to hereditary abnormalities in genes that regulate allergic reactions. As a result, some researchers believe that atopic eczema is an allergic reaction to increased Staphylococcus aureus colonization of the skin. A positive wheal and flare reaction to S. aureus antigens on a skin test is a defining feature of atopic eczema. Furthermore, multiple investigations have shown that persons with atopic eczema have an IgE-mediated response to S. aureus.

 

Signs and symptoms of Atopic disorders

In the following atopic diseases, there is a history of atopy (hypersensitivity to many allergens, and elevated IgE serum levels). Patients are symptom-free in the absence of exposure.

Allergic rhinitis(AR): 

It is also known as atopic rhinitis, which is described as an atopic disease characterized by nasal congestion, clear rhinorrhea, sneezing, postnasal drip, and nasal pruritis. It affects one out of every six people and is related with severe morbidity, productivity loss, and health-care expenses. Historically, atopic rhinitis was assumed to be a disease condition that only affected the nasal airway.

Nonetheless, the unified airway hypothesis classifies allergic rhinitis as a component of systemic allergic reaction, with other linked disorders, such as asthma and atopic dermatitis, sharing an underlying systemic pathology.

AR can be classified as seasonal (intermittent) or chronic (chronic), with around 20% of cases being seasonal, 40% perennial, and 40% having features of both. Patients with AR may also have allergic conjunctivitis, a non-productive cough, Eustachian tube dysfunction, and chronic sinusitis in addition to nasal symptoms. AR can be treated with a number of techniques if diagnosed, with intra-nasal glucocorticoids being the first-line treatment. Atopic rhinitis is mainly characterized by the following clinical manifestations:

• Nasal congestion. 
• Rhinorrhea. 
• Sneezing.  
• Itching of the nose.  
• Post-nasal drainage.  
• Dry cough.  
• Ocular symptoms. 
• Rhinoscopy shows a pale, swollen nasal mucosa with watery secretions.   
• The conjunctivae are hyperemic and edematous.

 

Allergic asthma: 

Allergic asthma is the most frequent kind of asthma. It is often defined by the existence of sensitivity to environmental allergens, however a clinical link between exposure and symptoms may also be present. Allergic asthma has a younger typical onset age than non-allergic asthma. Although the severity of allergic asthma can range from moderate to severe, studies have shown that allergic asthma is less severe than non-allergic asthma.

Patients with allergic asthma are more likely to develop allergic rhinoconjunctivitis and atopic dermatitis. Total IgE levels are often greater in allergic asthma compared to non-allergic asthma, however values significantly overlap between the two categories. Increased Th2 cytokines have been seen in allergic asthma patients' secretions and peripheral blood. Atopy has been found to be inversely related to chronic airflow restriction and airway remodelling. Patients with allergic asthma may exhibit any of the following symptoms:

• Frequent attacks of wheezing and dyspnea associated with chest tightness and coughing (often nocturnal in children) at times productive of thick and tenacious sputum.
• Fatigue.  
• Malaise.    
• Use of accessory muscles of respiration.
• The lung fields are hyper-resonant.  
• Diminished breath sounds, rhonchi, and wheezes on auscultation.  
• The expiratory phase is prolonged.  
• In severe attacks breath, sounds and wheezing may both be absent.

 

Atopic dermatitis:

Atopic dermatitis (AD), commonly known as atopic eczema, is a chronic skin disease (dermatitis). It causes itchy, red, puffy, cracked skin. Clear fluid may emerge from the afflicted locations, which frequently thickens with time. While the disorder can develop at any age, it usually begins in infancy and progresses in severity over time.

Much of the body may be impacted in children under the age of one year. The insides of the knees and elbows are the most typically afflicted sites in children as they get older. Adults are more typically afflicted in the hands and feet. Scratching the afflicted regions increases the symptoms, and people who are affected are more likely to get skin infections. Many people who have atopic dermatitis suffer from hay fever or asthma.

The etiology is unknown, however it is thought to entail genetics, immune system malfunction, environmental exposures, and skin permeability issues. If one identical twin has the disease, the other has an 85 percent probability of getting it as well. 

Those who live in cities or in arid climates are more likely to be harmed. Certain chemicals, as well as regular hand washing, aggravate symptoms. While emotional stress might exacerbate symptoms, it is not a cause. The condition is not communicable. Typically, a diagnosis is made based on the signs and symptoms. Contact dermatitis, psoriasis, and seborrheic dermatitis are some of the other disorders that must be ruled out before establishing a diagnosis.

Atopic dermatitis affects around 20% of the population at some time in their lives. Younger children are more prone to it. Both men and women are impacted equally. Many people grow out of the disease. Atopic dermatitis is sometimes known as eczema, which refers to a broader set of skin disorders. Other names for this condition include "infantile eczema," "flexural eczema," "prurigo Besnier," "allergic eczema," and "neurodermatitis." Patients may exhibit the following symptoms:

• The disease almost always begins in infancy.
• Itching that worsens at night and exacerbates by irritants such as wool.
• There is a strong family history of atopy.
• Scratching and rubbing cause the typical eczematous skin eruption to flare.
• Ingestion of allergenic food may cause exacerbations.
• The skin is typically dry and scaly.
• Presence of active skin lesions with prurigo and erythema. 
• Chronic lesions are thickened and lichenified.
• Distribution of the lesions is dependent on age - in childhood mostly affects the forehead and cheeks.

 

Food allergy:  

It is a faulty immunological reaction to food. The allergic reaction's symptoms might range from moderate to severe.Cow's milk, peanuts, eggs, shellfish, fish, tree nuts, soy, wheat, sesame, rice, and fruit are all common suspects.

A family history of allergies, a lack of vitamin D, obesity, and a high degree of hygiene are all risk factors. Allergies develop when immunoglobulin E (IgE), a component of the immune system, attaches to food components. The issue is generally a protein in the meal. This causes inflammatory molecules like histamine to be released. Food allergies can show as follows:

• Rhinoconjunctivitis.
• Respiratory symptoms alone are rare.
• Usually part of systemic anaphylaxis. 
• Hypotension.
• Arrhythmias.
• Nausea and vomiting.
• Abdominal cramping or diarrhea.

 

Diagnosis of Atopic disorders

Many atopic diseases are clinically diagnosed with a careful medical history and a comprehensive physical examination. A total blood cell count, immunoglobulin IgE levels, and a skin prick test are all used to detect acute hypersensitivity.

Quantitative Serum Immunoglobulins:

IgM, IgG, and IgA

 

Total Leukocyte Count and Differential:

• Hb (decreased in autoimmune hemolytic anemia).
• Eosinophilia. 
• Lymphocyte studies (CD4/CD8 count and suppressor T cells count that may be lower than the standard value).

 

Allergic test:

• Skin prick tests utilizing various allergens from animal, plants, food, pathogens and environmental pollutants
• The radioallergosorbent test (RAST): Use to determine specific IgE antibodies 

 

Other tests:

• Serum protein electrophoresis (to rule out IgE myeloma)
• Stool examination (for intestinal parasitism)
• Appropriate exclusion diet and blinded provocation (for food allergy diagnostic clarification)
• Chest X-ray (in bronchial asthma)

 

Treatment of Atopic disorders

Allergic rhinitis:

Environmental measures to prevent allergen exposure, medications, and desensitization are used to treat allergic rhinitis. As an allergic condition, the most effective treatment is avoidance of allergens on a prophylactic basis. However, avoidance is not always practicable since medications or desensitization are required to control symptoms.

Environmental measures include avoiding an allergen based on a clinical history of allergies rather than a positive skin test or RAST alone. Environmental control includes the removal of family pets, the frequent cleaning of house dust, and the avoidance of toys and other things. The usage of air-cleaning technologies might be beneficial. Pollen and outdoor mold development must be avoided.

Antihistamines are the most commonly used medications in allergic rhinitis and should be taken with caution to minimize side effects, while novel nonsedating antihistamines are now available to limit the most prevalent adverse effects. Nasal decongestants used orally in conjunction with antihistamines may be beneficial. Antihistaminic eye drops are essential for treating allergic conjunctivitis. Cromolyn nasal spray therapy four times per day is effective and has no acute or long-term harm. 

Systemic corticosteroids are very efficient in lowering allergic rhinitis symptoms, but because it is a chronic and benign illness, they should be used with caution. Desensitization (allergen injection treatment) should be administered to individuals whose symptoms have not been managed after earlier therapeutic approaches.

 

Allergic asthma:

The goal of symptomatic asthma is to manage the hyperirritable bronchial mucosa by environmental changes, medications, and other therapy.

Environmental control, as in atopic rhinitis, is part of the pharmacological treatment for bronchial asthma. The medication therapy involves the use of sympathomimetic beta-adrenergic bronchodilators, which are beneficial in acute attacks as well as long-term maintenance.

Subcutaneous administration of 0.2-0.5 mL of epinephrine is safe and effective. Albuterol, metaproterenol, pirbuterol, and isoetharine are selective beta-adrenergic bronchodilators that are administered through aerosol inhalation.

When used with sympathomimetic medicine, theophylline is a powerful bronchodilator. In an acute asthmatic episode, 250 to 500 mg of intravenous theophylline can be delivered quickly.

Glucocorticoids have proven to be extremely effective in the treatment of allergic asthma. Although their usefulness in asthma should be employed only after all other treatment alternatives have been exhausted. A daily dosage of 30 to 60 mg of prednisone is generally sufficient.

Cromolyn sodium (20 mg) is available as a metered-dose inhaler and as long-term preventive treatment. It will never reverse a severe assault. If secondary bacterial bronchitis or bronchopneumonia develops in allergic asthma, antibiotics may be used. Hydration and expectorants can help with thick sputum.

Desensitization works just as effectively in allergic asthma as it does in allergic rhinitis. Injection therapy for pollen hay fever is one example. In allergic asthma and atopic rhinitis, antileukotrienes such as montelukast and zafirlukast can be used.

 

Atopic dermatitis:

Atopic dermatitis manifests as a chronic skin illness that need good skin care, environmental management, medications, and allergy avoidance. The most effective preventative approach for skin itching is the use of nonirritating topical lubricants. 

When skin involvement is less severe, topical steroids are beneficial; but, in systemic eczema, systemic corticosteroids are required, generally starting with a high dose and gradually reducing until a therapeutic effect is achieved. Antihistamines used orally can help reduce itching. Patients should avoid taking frequent baths, as well as using irritating fabrics and strong detergents. If an infection arises, an antibiotic is required.

 

Food allergy:

A food allergy is treated by strictly avoiding the offending allergen. It is critical to have an emergency care plan and a documented anaphylactic action plan. It is vital to have self-injectable epinephrine and a medical alert bracelet on hand to inform healthcare providers to what is going on. Cow's milk, soy, wheat, egg, and peanut are the most frequent dietary allergens in children, accounting for 91% of responses. The most frequent allergies in adults include fish, shellfish, peanuts, tree nuts, eggs, fruits, and vegetables.

 

Outcome of Atopic disorders

Because atopic dermatitis is incurable, it has a lifetime proclivity for the development of allergic responses. Nonetheless, the signs of atopy frequently vary throughout time. Atopic dermatitis has a better prognosis and is treated with immunotherapy with moderate effectiveness. The prognosis of allergic asthma varies depending to the persistence of the causal environmental allergen, IgE levels in blood or tissues, and genetic composition.

Systemic anaphylaxis is the occurrence of an immunoglobulin E-mediated response in many organs at the same time. An insect venom, food, or medicine is the allergen. The response is potentially lethal and can be triggered by a trace amount of allergen. Anaphylaxis has a dismal prognosis and need rapid medical attention.

 

Conclusion

Atopy is the propensity to develop an excessive immunoglobulin E (IgE) immunological response to normally innocuous environmental chemicals. Allergic disorders are clinical symptoms of such improper, atopic reactions.

The clinical effect is an increased propensity to hypersensitivity responses. The most common manifestations of atopy are allergic bronchial asthma and allergic rhinitis, followed by atopic dermatitis and food allergies. Atopic conditions include allergic conjunctivitis, IgE-mediated drug allergy, urticaria and angioedema, and anaphylactic shock.

Atopy should be identified sooner, which typically necessitates early diagnosis by a pediatrician and referral to an allergy expert for disease confirmation and therapy. Later on, pulmonologists and dermatologists may be required. 

The patient should be educated by their main care practitioner, specialty-trained nurses, and pharmacists about keeping an allergy diary and having an epinephrine injector with them. To steer cases to the best possible solution, all of these specialists must work together as an inter-professional team.