Which of the following would be associated with increased IgE production?

• A. Transfusion reaction
• B. Reaction to poison ivy
• C. Activation of Th2 cells
• D. HDN

Answer: (C)

IgE production is driven by a Th2-type immune response. When Th2 cells are activated, they secrete cytokines such as IL-4 (and IL-13) that instruct B cells to switch to producing IgE. This IgE then binds to mast cells and basophils, fueling allergic reactions upon re-exposure to the allergen. So the concept tested is that a Th2-skewed response promotes class switching to IgE. Transfusion reactions involve antibodies against blood group antigens (often IgM or IgG), poisoning from plant allergens like poison ivy triggers a T-cell–mediated type IV response rather than IgE, and hemolytic disease of the newborn results from maternal IgG causing fetal RBC destruction.