Cytokines (
cyto, from
Greek "κύτταρο"
kyttaro "cell" +
kines, from Greek "κίνηση"
kinisi "movement") are a broad and loose category of small proteins (~5–20
kDa) that are important in
cell signaling. They are released by cells and affect the behavior of other cells. Cytokines can also be involved in
autocrine signaling. Cytokines include
chemokines,
interferons,
interleukins,
lymphokines,
tumour necrosis factor but generally not
hormones or
growth factors (despite some overlap in the terminology). Cytokines are produced by a broad range of cells, including immune cells like
macrophages,
B lymphocytes,
T lymphocytes and
mast cells, as well as
endothelial cells,
fibroblasts, and various
stromal cells; a given cytokine may be produced by more than one type of cell.