atopy
Summary
Atopy is a genetic predisposition to develop IgE-mediated hypersensitivity reactions to environmental allergens. It manifests as the classic triad of asthma, allergic rhinitis, and atopic dermatitis (eczema). This Type I hypersensitivity reaction involves Th2 cell activation and increased IgE production.
Detail
Atopy represents a hereditary tendency toward IgE-mediated allergic responses, characterized by overproduction of IgE antibodies against common environmental antigens (allergens). The pathophysiology involves Th2 cell predominance, leading to IL-4 and IL-13 secretion, which promotes B cell class switching to IgE production. Upon allergen re-exposure, cross-linking of IgE antibodies on mast cells and basophils triggers degranulation and release of inflammatory mediators (histamine, leukotrienes, prostaglandins). Clinically, atopy presents as the 'atopic march' - a progression from atopic dermatitis in infancy to food allergies, then asthma and allergic rhinitis in childhood. Key diagnostic features include elevated total IgE levels, positive skin prick tests or specific IgE (RAST) to environmental allergens, and family history of atopic diseases. The condition affects approximately 20% of the population in developed countries and is associated with hygiene hypothesis - reduced early-life microbial exposure may predispose to atopic diseases.
Sources
- Robbins Basic Pathology
- Janeway's Immunobiology
- Harrison's Principles of Internal Medicine
- First Aid for USMLE Step 1
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