Q15 - Classifying Hypersensitivity Reactions

Theoretical A Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license

There are four different types of hypersensitivity reactions in the human body, as can be seen in the list below.

TYPE I: Fast response which occurs in minutes, rather than multiple hours or days. Free antigens cross link the IgE on mast cells and basophils, which causes a release of vasoactive biomolecules.

TYPE II: IgG or IgM antibody binds to cellular antigen, leading to complement activation and cell lysis. IgG can also mediate Antibody Dependent Cell Cytotoxicity (ADCC) with cytotoxic T cells, natural killer cells, macrophages and neutrophils.

TYPE III: Antigen-antibody complexes are deposited in tissues. Complement activation provides inflammatory mediators and recruits neutrophils. Enzymes released from neutrophils damage tissue.

TYPE IV: Cell-mediated reactions are initiated by T-lymphocytes and mediated by effector T-cells and macrophages. This response involves the interaction of antigens with the surface of lymphocytes.

Match each of the following conditions with one of the hypersensitivities described above.

Q15.1. Match each scenario to one of the four hypersensitivity types (I: IgE/mast-cell, fast; II: IgG/IgM vs. cellular antigen + complement/ADCC; III: immune complexes deposited in tissue; IV: T-cell/macrophage-mediated). Which type matches: the reaction during a mismatched blood transfusion?

Q15.2. Which type matches: exposure to poison ivy, whose toxin binds human proteins and makes them self-antigens?

Q15.3. Which type matches: the reaction dermatologists use to identify specific food allergens patients are sensitive to (skin-prick testing)?

Q15.4. Which type matches: a reaction after pathogenic bacteria are destroyed by the immune system, but some of their macromolecules persist afterward?

Q15.5. Which type matches: a reaction that cannot be transferred from one patient to another via serum?

Q15.6. Which type matches: hay fever?

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Question reproduced from IBO 2019, Theoretical Exam A, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Official answer key