Final answer:
A T-cell's activation by its own secreted Interleukin-2 is an example of Autocrine signaling, where the signaling molecule acts upon the cell that produced it, leading to activation and proliferation.
Step-by-step explanation:
A T-cell's activation by the Interleukin-2 it secreted would best be described as Autocrine signaling.
Autocrine signaling is a form of cell signaling where a cell secretes a hormone or chemical messenger (called an autocrine agent) that binds to autocrine receptors on the same cell, leading to changes in the cell. This is distinct from other types of signaling such as paracrine, endocrine, and holocrine.
For T-cells, specifically, when a helper T cell recognizes an antigen, it can produce Interleukin-2. This Interleukin-2 then binds to receptors on the surface of the same T cell that produced it, which leads to the T cell's activation, proliferation, and differentiation. This process is crucial in the cellular immune response as it ensures a robust defense against pathogens.