Which cytokine is primarily responsible for promoting IgE class switching in B cells during allergic responses?

• A. Interleukin-2
• B. Interleukin-10
• C. Interleukin-4
• D. Tumor necrosis factor-alpha

Answer: (C)

IgE production by B cells in allergic reactions is driven by signals that push the B cell to switch its antibody production from IgM to IgE. The cytokine most closely tied to this process is interleukin-4. It is produced by Th2 cells in the allergic milieu and binds to the IL-4 receptor on B cells, triggering the JAK-STAT pathway with STAT6 as a key mediator. This signaling promotes germline transcription of the epsilon (ε) switch region and enables activation-induced cytidine deaminase to initiate class switch recombination to IgE. The result is increased IgE production, which binds to FcεRI on mast cells and basophils and drives allergic responses. While IL-13 can work alongside IL-4 to boost IgE, IL-4 remains the primary driver of this specific switch. Other cytokines like IL-2 or TNF-α do not directly steer IgE switching in the same way.