Which of the following cytokines acts as a costimulator for T helper cells?

• A. Granulysin
• B. Interleukin 1
• C. Interleukin 2
• D. Lymphotoxins

Answer: (C)

Interleukin 2 (IL-2) plays a significant role as a costimulator for T helper cells, making it essential for their activation and proliferation. When T cells recognize an antigen presented by an antigen-presenting cell (APC), additional signals are necessary to fully activate these cells. IL-2 is produced primarily by activated T helper cells and stimulates their growth, differentiation, and survival.

The presence of IL-2 among activated T cells leads to a positive feedback loop, promoting further T cell activation and enhancing the immune response. This process is crucial for the effective functioning of the adaptive immune system, as it helps ensure that T cells are adequately amplified in response to pathogens.

In contrast, the other options listed do not function primarily as costimulators for T helper cells in the same way as IL-2. Granulysin is involved in the cytotoxic activity of certain immune cells, while interleukin 1 is primarily a pro-inflammatory cytokine that enhances immune responses but does not directly act as a costimulator for T helper cells. Lymphotoxins are involved in inducing apoptosis in infected or cancerous cells and are not focused on T cell stimulation.