What is human interleukin 2?

interleukin-2 (IL-2) is an interleukin, a type of cytokine signaling molecule in the immune system. It is a 15.5–16 kDa protein[5] that regulates the activities of white blood cells (leukocytes, often lymphocytes) that are responsible for immunity. IL-2 is part of the body's natural response to microbial infection, and in discriminating between foreign ("non-self") and "self". IL-2 mediates its effects by binding to IL-2 receptors, which are expressed by lymphocytes. The major sources of IL-2 are activated CD4+ T cells and activated CD8+ T cells

Explanation:

In homeostasis fashion, cells undergo balanced cell division and programmed cell death (apoptosis) through regulated signalling.This maintains tissue integrity. On the one hand, Proto-oncogenes promotes cells proliferation. On the other hand, tumors suppressors inhibit cell growth and division especially in cells with damaged dna.
Therefore mutations on these oncogenes could result to uncontrolled cell proliferation. Cancer cells also overexpress angiogens that results to proliferation of blood vessels in tumors. This contributes to their metastasis in the body.