What type of feedback system is demonstrated when T helper cells proliferate upon releasing IL-2?

• A. Negative feedback system
• B. Homeostatic feedback system
• C. Positive feedback system
• D. Regulatory feedback system

Answer: (C)

The scenario described involves T helper cells proliferating in response to the release of interleukin-2 (IL-2), which is a clear example of a positive feedback system. In this context, when T helper cells activate and produce IL-2, this cytokine acts on those same T helper cells as well as nearby T cells, promoting their growth and further stimulation. This self-amplifying cycle enhances the immune response, increasing the number of T cells that can help in fighting infections.

A positive feedback system is characterized by an initial stimulus that produces a response that further amplifies that stimulus. In the case of T helper cells, the release of IL-2 strengthens the proliferation of these cells, thus perpetuating the cycle effectively. This mechanism is crucial during an immune response, as it ensures a rapid and robust activation of T cells when needed, such as during an infection.

Other feedback systems, like negative feedback, work to reduce or inhibit a process, homeostatic feedback involves maintaining balance without amplifying a response, and regulatory feedback typically refers to controlling or modulating biological functions rather than necessarily increasing cell populations. These systems do not apply in this scenario as there is a clear escalation of activity rather than a moderation or maintenance of balance.