Which cytokine is primarily produced by T cells and drives T cell proliferation?

• A. Interleukin-4
• B. Interleukin-2
• C. Interleukin-6
• D. Interferon-gamma

Answer: (B)

T cell proliferation after antigen recognition is driven by a growth factor that T cells themselves produce, creating an autocrine signal. This cytokine is interleukin-2. Activated T cells secrete IL-2, which then binds to the IL-2 receptor on the same or neighboring T cells, promoting clonal expansion and proliferation. The receptor comes in high affinity form when its alpha chain (CD25) is upregulated on activation, making the signal potent and sustained during the immune response.

IL-2 also helps expand other cytotoxic and helper T cells and can support NK cell proliferation, but its central role is driving the expansion of antigen-specific T cells after they’re activated. In contrast, interleukin-4 is more about Th2 responses and B cell help, interleukin-6 is a broader inflammatory mediator with wide sources, and interferon-gamma largely activates macrophages and shapes Th1 responses rather than initiating T cell proliferation.