Which cytokines promote B cell class switching to different Ig isotypes (e.g., IgG, IgA, IgE)?

• A. IL-2 alone
• B. TGF-β alone
• C. IL-10 alone
• D. Cytokines from helper T cells (e.g., IL-4 and IFN-γ) drive class switch recombination

Answer: (D)

B cells change the antibody constant region through class switch recombination, and the signals that drive this switching come from helper T cells. The cytokines they release direct CSR toward different isotypes. For example, IL-4 promotes switching to IgE (and IgG4 in humans), IFN-γ steers switching to certain IgG subclasses, and TGF-β promotes IgA. This coordinated set of signals from helper T cells explains why class switching to multiple isotypes occurs. Relying on a single cytokine in isolation doesn’t capture how CSR is guided across different isotypes, and cytokines like IL-2 or IL-10 don’t primarily drive CSR to multiple isotypes.