Final answer:
Interleukin-2 stimulating the proliferation of the T cells that produced it is an example of an autocrine effect, which is a type of cell signaling where a cell targets itself.
Step-by-step explanation:
Interleukin-2 (IL-2) is one of the cytokines that plays a critical role in the function of the immune system, particularly in the growth and activity of T cells.
When IL-2 stimulates proliferation in the T cells that secreted it, this property is referred to as an autocrine effect.
The other options listed – paracrine, endocrine, and singleton effects – describe different modes of signaling: paracrine refers to cell signaling over a short distance to nearby cells, endocrine refers to hormones released into the bloodstream to act on distant cells, and singleton effect is not a recognized term in this context.