**Core Concept:** The question is asking about the most potent stimulator of native T cells, which are a type of white blood cell responsible for cell-mediated immunity. T cells play a crucial role in the immune response against pathogens and cancer cells.

**Why the Correct Answer is Right:** Interleukin-2 (IL-2) is the most potent stimulator of native T cells. Interleukins are a family of signaling proteins that regulate immune system function, including T cell activation and proliferation. In the context of T cell activation, IL-2 acts as a positive feedback loop, amplifying the immune response.

**Why Each Wrong Option is Incorrect:**

A. Interleukin-4 (IL-4) is a lymphokine that suppresses T cell activation, making it an incorrect choice.
B. Interleukin-7 (IL-7) is a cytokine that promotes B cell development and T cell survival but is less potent than IL-2 in stimulating T cell proliferation.
C. Interleukin-15 (IL-15) is a cytokine involved in T cell activation, but it is even less potent than IL-7 in stimulating T cell proliferation.
D. Interleukin-12 (IL-12) is a cytokine that promotes Th1 differentiation but does not stimulate T cell proliferation as strongly as IL-2.

**Clinical Pearl / High-Yield Fact:** IL-2 is crucial in regulating immune responses, particularly in autoimmune diseases like multiple sclerosis and type 1 diabetes, where excessive T cell activation and autoimmunity occur. Understanding the role of IL-2 and its interactions with other cytokines is essential for understanding the intricacies of the immune system and immune-related disorders.

**Correct Answer:** D. Interleukin-12 (IL-12) is a cytokine that promotes Th1 differentiation but does not stimulate T cell proliferation as strongly as IL-2.