Atopy

Synonym: Localized Anaphylaxis 

Introduction:

Atopy is defined as the tendency of an individual to produce IgE antibodies in response to various environmental antigens and thus develop strong immediate hypersensitivity (allergic) responses. Individuals with allergies to environmental antigens (e.g., pollen, house dust) are atopic. 

Localized anaphylaxis involves reactions limited to a specific target tissue or organ and often involves epithelial surfaces at the site of allergen entry. Atopy is thus defined as the tendency to manifest localized anaphylactic reactions, and this tendency is inherited. 

Atopic allergies include a wide range of IgE-mediated disorders, including allergic rhinitis (hay fever), asthma, atopic dermatitis (eczema), and food allergies. 

Allergic Rhinitis:

This is commonly known as “hay fever” and results from the reaction of airborne allergens with the sensitized mast cells in the conjunctivae and nasal mucosa, which induces the release of pharmacologically active mediators from mast cells. The mediators thus cause localized vasodilation and increased capillary permeability. The symptoms of allergic rhinitis usually include watery exudation of the conjunctivae, upper respiratory tract and nasal mucosa, and sneezing and coughing.

Asthma:

Asthma, a common manifestation of localized anaphylaxis, is triggered by degranulation of mast cells with the release of mediators, but instead of occurring in the nasal mucosa, the reaction develops in the lower respiratory tract. This results in the contraction of the bronchial smooth muscles and thus eventually leads to broncho-constriction. 

Food Allergies:

A variety of foods can induce localized anaphylaxis in allergic individuals. In addition, localized smooth-muscle contraction and vasodilation can be induced by allergen cross-linking of IgE on mast cells along the upper or lower gastrointestinal tract resulting in symptoms such as vomiting or diarrhea. 

Atopic Dermatitis:

Atopic dermatitis (allergic eczema) is an inflammatory disease of the skin frequently associated with a family history of atopy. This disease is observed most commonly among young children, often developing during infancy. Serum IgE levels are often elevated, and the allergic individual develops erythematous skin eruptions filled with pus. 

Article by- SAMPRATI PAREKH  (MSIWM049)

References:

1. Cellular and Molecular Immunology by Abul K. Abbas – 7^thEdition 
2. Kuby Immunology – 5^thEdition.