Hypersensitivity Reactions Practice Test

Type I: Allergen cross-links IgE on mast cells causing immediate wheal-and-flare and possible anaphylaxis within minutes

Nonimmune: Irritant dermatitis from acids causing immediate burning pain without prior sensitization or immune memory

Type IV: Sensitized T cells mediate delayed inflammation and epidermal damage 48–72 hours after exposure to urushiol

Type III: Immune complexes deposit in small vessels causing palpable purpura, arthralgia, and low complement

Type II: IgG binds to cell-surface antigens causing complement activation and cell destruction with a positive Coombs test