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Cytokine

(Science: biochemistry) small proteins or biological factors (in the range of 5-20 kD) that are released by cells and have specific effects on cell-cell interaction, communication and behaviour of other cells.

Not really different from hormones, but the term tends to be used as a convenient generic shorthand for interleukins, lymphokines and several related signalling molecules such as TNF and interferons.

Generally growth factors would not be classified as cytokines, though tgf is an exception. Rather an imprecise term. Chemokines are a subset of cytokines.