Hypersensitivity Reactions: Types I-IV
Start with the big picture
Type I reactions begin rapidly when allergen-linked IgE activates mast cells and basophils, releasing inflammatory mediators. Types II and III involve antibodies and complement, but differ in how tissue injury occurs: Type II antibodies bind cell or extracellular-matrix targets, while Type III immune complexes deposit in tissues and recruit inflammatory damage. Type IV is delayed and driven by sensitized T cells rather than antibodies. The lesson connects these mechanisms with representative conditions and diagnostic clues, including immunofluorescence patterns and laboratory markers. It also introduces clinical management concepts, from emergency care for anaphylaxis to approaches that target allergic pathways or broader immune activity. Some diseases can involve more than one hypersensitivity mechanism.
What you'll learn
- Compare the mechanisms and timing of Type I, II, III, and IV hypersensitivity reactions.
- Relate representative diseases to their hypersensitivity types.
- Interpret key diagnostic patterns, including immunofluorescence findings and relevant markers.
- Explain how overlapping mechanisms can occur in a single disease.
- Describe treatment strategies associated with Type I reactions and Types II–IV.
Continue your study
Work through the complete notes and reinforce the topic with the study tools available in the full lesson.
