Which cytokine is a major antagonist to IFN-γ?

• A. IL-10
• B. IL-4
• C. TNF-α
• D. TGF-β

Answer: (A)

Understanding how cytokines regulate Th1 vs Th2 responses helps explain why IL-10 is the best answer. IFN-γ is the key Th1 cytokine that activates macrophages and drives cell-mediated immunity. IL-10 acts as a strong anti-inflammatory regulator that dampens this arm of the immune response: it inhibits macrophage activation, reduces MHC II expression, and suppresses production of IL-12 and other pro-inflammatory signals, which in turn lowers IFN-γ production by T and NK cells. Because of these broad inhibitory effects specifically targeting the pathways IFN-γ promotes, IL-10 serves as a major antagonist to IFN-γ. Other options either promote Th2 responses (which can indirectly reduce IFN-γ) or are not primarily antagonistic to IFN-γ—TNF-α tends to work with IFN-γ in macrophage activation, and TGF-β, while anti-inflammatory, is not as central to opposing IFN-γ as IL-10.