General term for protein messengers that regulate immune responses.
Cytokines are secreted by macrophages, monocytes, lymphocytes, neutrophils, and several non-immune cell types.
They function both locally and as hormones.
Cytokines are peptides that, in immune and inflammatory reactions, are released from and regulate the action of inflammatory and immune system cells.
The cytokine superfamily includes the interferons, numerous interleukins, tumor necrosis factor (TNF), various growth factors, the chemokines and the colony stimulating factors (CSF).