Complex sentence: Interleukin-2 (IL-2) is an interleukin, a type of cytokine immune system signaling molecule, which is a leukocytotrophic hormone that is instrumental in the body's natural response to microbial infection and in discriminating between foreign (non-self) and self.
Split into simpler sentences: Interleukin-2 (IL-2) is an interleukin, a type of cytokine signaling molecule in the immune system. It is part of the body's natural response to microbial infection, and in discriminating between foreign (non-self) and self.