Snapshot A 12-year-old boy presents to the emergency department with dyspnea and urticaria. His symptoms began approximately 30 minutes after being stung by bee. Medical history is significant for asthma and an allergy to shellfish. On physical exam, breathing is labored, and wheezes are appreciated on pulmonary auscultation. Airway, breathing, and circulation is intact. The boy is immediately started on intramuscular epinephrine. (Anaphylaxis) Introduction Hypersensitivity reactions (HSR) can be considered as an overreactive immune response HSR can be classified into four categories login to view 3 more bullets Speed of reaction login to view 2 more bullets Type I HSR (Anaphylactic and Atopic) Mechanism of action login to view 16 more bullets Clinical disorders login to view 1 more bullet Diagnostic testing login to view 2 more bullets Type II HSR (Cytotoxic) Mechanism of action login to view 6 more bullets Clinical disorders login to view 1 more bullet Diagnostic testing login to view 4 more bullets Type III HSR (Immune-Complex) Mechanism of action login to view 3 more bullets Clinical disorders login to view 1 more bullet Type IV HSR (Cell-Mediated) Mechanism of action login to view 6 more bullets Clinical disorders login to view 1 more bullet Summary Hypersensitivity Reactions Hypersensitivity Reaction Type Pathophysiology Clinical Examples Type I (anaphylactic and atopic) Immediate Antigens cross-linkIgE antibodiestriggering vasoactive amine release (e.g., histamine) Anaphylaxis allergens bee sting food (e.g., peanuts) drugs Asthma allergens inhaled materials Allergic rhinitis allergens animals trees Type II (cytotoxic) Antibodies are directed against cell-surface antigens resulting in opsonization complement activation neutrophil and macrophage recruiting NK cell killing impairment of cellular function Autoimmune hemolytic anemia antigen erythrocyte membrane proteins Acute rheumatic fever antigen myocardial antigens via cross-reacting with S. pyogenes M protein Goodpasture syndrome antigen type IV collagen Immune thrombocytopenic purpura antigen platelet membrane proteins Myasthenia gravis antigen acetylcholine receptors Graves' disease antigen TSH receptors Erythroblastosis fetalis antigen Rh antigen Pemphigus vulgaris antigen desmosomes Type III (immune-complex) IgG antibodies complexes withself or foreign antigensresulting in complement activation Serum sickness Arthus reaction Systemic lupus erythematosis Polyarteritis nodosa Poststreptococcal glomerulonephritis Type IV (cell mediated) CD8+ T-cells directly destroy the target cell Pre-sensitized CD4+ helper T-cell releases cytokines when re-exposed to the offending material Notice this does NOT involve antibodies Type I diabetes meilltus Contact dermatitis Tuberculin test Sympathetic ophthalmia