A general term used to describe a large array of relatively small proteins that are either secreted by a cell to alter its own function (autocrine
effect) or the function of adjacent cells (paracrine
effect). Some cytokines can affect many different systems, giving them functional redundancy if one is missing (i.e. cytokines involved in immune signalling
and the inflammation
Examples of cytokines include the interleukins and various growth factors.
Cytokines often participate in a cytokine network where one cytokine will trigger release of other cytokines. With redundancy built into the network, it is resistant to defects in case one component gets knocked out.