Which cytokines drive class switching to IgE in B cells?

• A. IFN-γ
• B. IL-2
• C. IL-12
• D. IL-4

Answer: (D)

The main idea is that antibody class switching is directed by the cytokine signals present during B cell activation. IL-4 from Th2 cells binds to the IL-4 receptor on B cells and activates the JAK-STAT6 pathway. This signaling induces ε germline transcription and, with the action of Activation-Induced Cytidine Deaminase (AID), directs recombination from the μ constant region to the ε region, producing IgE-producing B cells. IL-13 can use the same receptor pathway and support IgE switching as well, but IL-4 is the primary driver. In contrast, IFN-γ pushes switching toward other IgG subclasses and tends to suppress IgE, while IL-12 promotes a Th1 response (increasing IFN-γ) and IL-2 mainly supports T cell growth rather than CSR. So IL-4 is the cytokine that drives class switching to IgE.