Which cytokine is most closely associated with promoting IgE class switching in B cells?

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

Answer: (C)

Cytokine signals guide B cells through class switch recombination, and IL-4 is the strongest driver of switching to IgE. When IL-4 binds its receptor on a B cell, it activates the JAK-STAT6 pathway. STAT6 promotes transcription of the epsilon heavy-chain region (germline ε transcription) and, together with activation-induced cytidine deaminase (AID), enables the recombination that replaces the μ constant region with ε. The result is B cells that can produce IgE antibodies. This Th2-associated cytokine environment is a hallmark of allergic responses, where IL-4 (and to some extent IL-13) pushes CSR toward IgE. By contrast, IFN-γ steers switching toward other isotypes like IgG subclasses and can oppose IgE formation; IL-2 mainly supports T cell growth, and TNF-α is an inflammatory mediator not a primary driver of CSR to IgE.