What is a hypersensitivity reaction? An inappropriate overreaction of the immune system to an otherwise harmless antigen
How many types of hypersensitivity reactions exist? Four
What mediates Type I hypersensitivity? IgE antibodies
What mediates Type II hypersensitivity? IgG or IgM antibodies
What mediates Type III hypersensitivity? Immune complexes via complement activation
What mediates Type IV hypersensitivity? Delayed cellular response
An acute, potentially lethal multisystem syndrome caused by sudden release of mast cell and
What is anaphylaxis?
basophil mediators
Is anaphylaxis IgE-mediated? yes
What type of hypersensitivity reaction is anaphylaxis? Type I immediate hypersensitivity
What is an anaphylactoid reaction? A reaction that mimics anaphylaxis but is not IgE-mediated
Does an anaphylactoid reaction require prior sensitization? no
Does anaphylaxis require prior sensitization? yes
How are anaphylactic and anaphylactoid reactions managed? The same way as both are potentially life-threatening
Allergen binds IgE on mast cells/basophils ’intracellular signaling ’degranulation ’releasing
What is the key pathophysiologic step in anaphylaxis? performed mediators ’the mediators act directly on the tissue or recruit additional inflamma-
tory cells ’recruited cells release more mediators
What preformed mediators are released during degranulation? Histamine, tryptase, tumor necrosis factor (TNF)
vasodilation, increased vascular permeability, increased heart rate, increased cardiac contrac-
What are the ettects of histamine?
tion, glandular secretion
What are the ettects of tripase? activates complement and coagulation
What are the ettects of prostaglandin D2? Vasodilation, increased vascular permeability, bronchoconstriction
Increased microvascular permeability, potent bronchoconstriction, enhanced mast cell de-
What are the ettects of leukotrienes?
granulation
What are the ettects of PAF? Decreased coronary blood flow, delayed AV conduction, negative inotropic ettects
What is the ettect of nitric oxide in anaphylaxis? Potent vasodilation ’worsened vascular permeability and hypotension
What is the key pathophysiologic step in anaphylactoid reactions? Direct mast cell/basophil activation without IgE involvement
At what step does anaphylactoid reaction begin? Mast cell degranulation (bypasses IgE formation and binding)
The same as anaphylaxis: histamine, tryptase, TNF, prostaglandins, leukotrienes, PAF, nitric
What mediators are released in anaphylactoid reactions?
oxide
What agents most commonly trigger immune-mediated anaphylaxis? Foods, medications, insect stings, and natural rubber latex
What medications most commonly cause anaphylaxis? Antibiotics (especially beta-lactams)
What foods most commonly cause anaphylaxis? peanuts and tree nuts
What causes Vancomycin infusion reaction? Direct mast cell activation by vancomycin ’histamine release
What is the classic presentation of VIR? Pruritic erythematous rash of face, neck, upper torso ("Red Man Syndrome")
Can VIR cause hypotension and angioedema? Yes in up to 15% of patients.
What skin findings are common in anaphylaxis? Hives, itching, flushing, swollen lips/tongue/uvula, periorbital edema, conjunctival swelling
Nasal discharge, congestion, sneezing, throat itching, voice change, throat tightness, stridor,
What respiratory symptoms are common?
SOB, wheeze, cough
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How many types of hypersensitivity reactions exist? Four
What mediates Type I hypersensitivity? IgE antibodies
What mediates Type II hypersensitivity? IgG or IgM antibodies
What mediates Type III hypersensitivity? Immune complexes via complement activation
What mediates Type IV hypersensitivity? Delayed cellular response
An acute, potentially lethal multisystem syndrome caused by sudden release of mast cell and
What is anaphylaxis?
basophil mediators
Is anaphylaxis IgE-mediated? yes
What type of hypersensitivity reaction is anaphylaxis? Type I immediate hypersensitivity
What is an anaphylactoid reaction? A reaction that mimics anaphylaxis but is not IgE-mediated
Does an anaphylactoid reaction require prior sensitization? no
Does anaphylaxis require prior sensitization? yes
How are anaphylactic and anaphylactoid reactions managed? The same way as both are potentially life-threatening
Allergen binds IgE on mast cells/basophils ’intracellular signaling ’degranulation ’releasing
What is the key pathophysiologic step in anaphylaxis? performed mediators ’the mediators act directly on the tissue or recruit additional inflamma-
tory cells ’recruited cells release more mediators
What preformed mediators are released during degranulation? Histamine, tryptase, tumor necrosis factor (TNF)
vasodilation, increased vascular permeability, increased heart rate, increased cardiac contrac-
What are the ettects of histamine?
tion, glandular secretion
What are the ettects of tripase? activates complement and coagulation
What are the ettects of prostaglandin D2? Vasodilation, increased vascular permeability, bronchoconstriction
Increased microvascular permeability, potent bronchoconstriction, enhanced mast cell de-
What are the ettects of leukotrienes?
granulation
What are the ettects of PAF? Decreased coronary blood flow, delayed AV conduction, negative inotropic ettects
What is the ettect of nitric oxide in anaphylaxis? Potent vasodilation ’worsened vascular permeability and hypotension
What is the key pathophysiologic step in anaphylactoid reactions? Direct mast cell/basophil activation without IgE involvement
At what step does anaphylactoid reaction begin? Mast cell degranulation (bypasses IgE formation and binding)
The same as anaphylaxis: histamine, tryptase, TNF, prostaglandins, leukotrienes, PAF, nitric
What mediators are released in anaphylactoid reactions?
oxide
What agents most commonly trigger immune-mediated anaphylaxis? Foods, medications, insect stings, and natural rubber latex
What medications most commonly cause anaphylaxis? Antibiotics (especially beta-lactams)
What foods most commonly cause anaphylaxis? peanuts and tree nuts
What causes Vancomycin infusion reaction? Direct mast cell activation by vancomycin ’histamine release
What is the classic presentation of VIR? Pruritic erythematous rash of face, neck, upper torso ("Red Man Syndrome")
Can VIR cause hypotension and angioedema? Yes in up to 15% of patients.
What skin findings are common in anaphylaxis? Hives, itching, flushing, swollen lips/tongue/uvula, periorbital edema, conjunctival swelling
Nasal discharge, congestion, sneezing, throat itching, voice change, throat tightness, stridor,
What respiratory symptoms are common?
SOB, wheeze, cough
1/4
