Which cytokine is most associated with B cell class switching to IgE in allergic responses?

• A. Interleukin-4
• B. Interleukin-2
• C. Interleukin-6
• D. Interferon-gamma

Answer: (A)

In allergic responses, B cells switch to producing IgE mainly under the influence of IL-4. This cytokine, produced by Th2 cells (and also by mast cells and basophils in allergic environments), engages receptors on B cells and activates signaling that promotes switching from IgM to the epsilon constant region, leading to IgE production. The shift to IgE is a hallmark of Th2-dominated responses and underpins the sensitization of mast cells and basophils, which drives immediate hypersensitivity upon re-exposure to the allergen.

Other cytokines don’t specifically steer this switch: IL-2 mainly promotes T cell growth, IL-6 supports B cell differentiation into antibody-secreting cells in a more general way, and IFN-gamma from Th1 responses encourages switching to other isotypes like IgG and can counteract IgE production.