cytokines

n. protein released by lymph cells which acts as a cellular mediator and controls immune response (Physiology)

Cytokines are a group of proteins and peptides that are used in organisms as signaling compounds. These chemical signals are similar to hormones and neurotransmitters and are used to allow one cell to communicate with another. The cytokine family consists mainly of smaller water-soluble proteins and glycoproteins (proteins with an added sugar chain) with a mass of between 8 and 30 kDa. While hormones are released from specific organs into the blood and neurotransmitters are released by nerves, cytokines are released by many types of cells. They are particularly important in both innate and adaptive immune responses. Due to their central role in the immune system, cytokines are involved in a variety of immunological, inflammatory and infectious diseases. However, not all their functions are limited to the immune system, as they are also involved in several developmental processes during embryogenesis.
See more at Wikipedia.org...

Cytokines Chemicals made by the cells that act on other cells to stimulate or inhibit their function. [more]Cytokines - Community and Resources

Noun
1. any of various proteins secreted by cells of the immune system that serve to regulate the immune system
(hypernym) protein
(hyponym) tumor necrosis factor, tumour necrosis factor, TNF