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Published byClifford Jordan Modified over 9 years ago
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Hypersensitivity Reactions
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Injurious, patologic immune reactions causing tissue injury and disease Excessive or aberrant immune response to: Foreign antigens (non-self) - non-infectious (environmental) - infectious Self (autologous) antigens failure of self-tolerance (autoimmunity, autoimmune diseases)
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Types of Hypersensitivity Reactions Type I Type II Type III Type IV Antibody mediated T cell mediated
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Type I (Immediate hypersensitivity) (Allergy) Atopy – inherited propensity of an individual to produce high levels of IgE to various environmental antigens Alergen – an antigen that induces immediate hypersensitivity in atopic people
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"in recognition of his work on anaphylaxis" Charles Richet 1913 Nobel Prize of Medicine and Physiology
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Common allergens
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Food allergens (“the big eight”)
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The sequence of events
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Type I hypersensitivity
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Biochemical events in mast cell activation
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High level IgE production is determined by: Genetic factors (MHC II, cytokines, cytokine receptors...) Nature of allergen (mass, glycosylation, charge, stability) Environmental factors (exposure to microbes, polution, smoking...)
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Clinical manifestasions Alergic conjuctivitis Alergic rhinitis (hay fever) Alergic (bronchial) asthma Hives (Urticaria) Atopic dermatitis Food allergy Anaphylaxis (systemic)
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Testing for type I hypersensitivityin vivo Skin tests Prick testing Intradermal testing Provokativni testovi Bronchoprovocative tests (metacholin chloride or alergen) DBPCFC (Double-Blind Placebo-Controlled Food Challenge)
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15 min. Prick testing Swelling 2mm › negative control – positive ≥ 5mm – clinically relevant 5-10 mm weak sensitivity 10-15 mm moderate sensitivity › 15 mm strong sensitivity Swelling and redness
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Testing for type I hypersensitivityin vitro Total IgE nephelometry...
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Alergen specific IgE RAST (RadioAllergoSorbent Test) EIA (PHADIA ImmunoCap...)
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Therapy Inhibition of mast cell degranulation (cromolyn) Blocking of mast cell mediator effects (antihistamines) Reduction of inflammation (corticosteroids) Bronchial smooth muscle relaxation (phosphodiesterase inhibitors) “Desensitization” – repeated administration of allergen Epinephrine - anaphylaxis
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