Hypersensitivity Flashcards
Hypersensitivity Definition
Hyperactive immune responses against “harmless” antigens
Hypersensitivity 1: The allergic Reaction
Immediate Reaction to allergen: MAST CELLS AND BASOPHILS
Late Phase Reaction: Caused by mediators released, they recruit inflammatory cells such as EOSINOPHILS AND NEUTROPHILS
Mediators of Type I Hypersensitivity
-
Histamine:
- Vasodilation
- Increased capillary permeability
- Smooth muscle contraction (bronchospasm)
-
Prostaglandins
- Bronchoconstriction
-
Leukotrienes
- Capillary permeability
-
TNF-a, IL-4
- Inflammation
Allergen Definition
Small inhaled proteins that stimulate IgE production in atopic (tendency to develop allergy) individuals
Effective Allergen Traits
- Small, highly soluble
- Low dose
- Carried on dry particles (pollen)
What is difference between non-atopic and atopic individuals?
Non-atopic: IgG Ab
Atopic: IgE Ab
Hygiene hypothesis (childhood)
Early microbial infections important in biasing toward Th1 response to environmental allergens
Western hemisphere has better hygiene so less infections and therefore, more allergies.
Why do some people have allergies?
- Th2 bias developed as a fetus
- Lack of childhood infection maintains Th2 bias
- Genetic predisposition towards allergies
- Lack of Tregulatory response to allergen
Treatments for Allergies
- Bronchodilators (treats bronchoconstriction)
- Antihistamines (block histamine receptors)
- Corticosteroids (block cytokine production, therefore less Ab)
- Omalizumab (anitbody that blocks binding to mast cells, relieves symptoms and severity of asthma)
- Mast cell membrane stabilizers (prevents mast cell breakdown)
- Leukotriene modifiers (inhibits leukotriene)
Only successful approach for CURE of allergy?
Specific Immunotherapy
Types of Hypersensitivity Table
Type II Hypersensitivity: Cytotoxic
Type III: Immune Complex
Antigen-antibody complex induce inflammation in tissues
Persistant microbial or viral infections
Autoimmune disorders
Type IV: Delayed
Macrophage ingests antigen, and presents an epitope on its surface with MHC II protein
Activates macrophages via Th1
Function of T-lymphocytes
Delayed: starts hours, days, after contact w antigen and lasts for days
Types: Contact hypersensitivity, Tuberculin-type
Differences between types of hypersensitivity?
Types I, II, and III are ANTIBODY-mediated, while Type IV is cell-mediated (T) and delayed. Type I are mediated by IgE, whereas types II and III are mediated by IgG and involve complement.
