ImmunologyLesson 1 of 4 in the course Diseases of the Immune System

Hypersensitivity Mechanisms, Clinical Patterns, and Management

5 flashcards · 5 quiz questions · 5 match pairs · 5 fill-in sentences · English

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Summary

Hypersensitivity reactions occur when immune defenses cause harmful or disproportionate effects in the body. This lesson introduces the four-part classification and explains how type I hypersensitivity produces allergies and anaphylaxis.

Hypersensitivities are classified by the immune mechanism that causes tissue damage.

An allergen is an antigen that provokes an allergic response. Examples include pollen, mold, animal dander, foods, insect venom, and some drugs. During an initial exposure in a susceptible person, T_H2 cells release IL-4 and IL-13, stimulating allergen-specific B cells to switch antibody production to IgE. IgE binds by its Fc region to receptors on mast cells. This initial process is called sensitization; it often causes no symptoms by itself.

All flashcards

What is sensitization in type I hypersensitivity?
An initial exposure leads to allergen-specific IgE binding to mast cells, priming them for a later exposure.
How does allergen cross-linking activate a sensitized mast cell?
It links mast-cell-bound IgE molecules and triggers degranulation and mediator release.
What causes tissue injury in type III hypersensitivity?
Deposited antigen–antibody complexes activate complement and inflammatory cells.
What is the defining immune mechanism of type IV hypersensitivity?
T cells and the effector cells they activate cause tissue injury.
What is a late-phase type I reaction?
A delayed inflammatory response involving recruited immune cells and additional mediator release.

Quiz questions

  1. Which mechanism defines type III hypersensitivity?Answer: Soluble antigen–antibody complexes deposit in tissues and trigger inflammation.
  2. Which antibodies are generally present in type O plasma?Answer: Anti-A and anti-B antibodies.
  3. How can maternal anti-D antibodies cause hemolytic disease of the newborn?Answer: Maternal IgG crosses the placenta and destroys fetal Rh-positive red blood cells.
  4. What does a positive Mantoux tuberculin skin test establish by itself?Answer: Immune recognition of tuberculin, but not necessarily active tuberculosis.
  5. Which medication is the immediate first-line treatment for anaphylaxis?Answer: Epinephrine.

Based on Microbiology by Nina Parker, Mark Schneegurt, Anh-Hue Thi Tu, Philip Lister, Brian M. Forster (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.

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