Several inflammatory cytokines are induced by oxidative stress.and also lead to increased oxidative stress makes them important in chronic inflammation, as well as other immunoresponses, such as fever and acute phase proteins of the liver (IL-1,6,12, IFN-a).
Part of the difficulty with distinguishing cytokines from hormones is that some of the immunomodulating effects of cytokines are systemic rather than local.
For instance, to use hormone terminology, the action of cytokines may be autocrine or paracrine in chemotaxis or chemokinesis and endocrine as a pyrogen.
They act through receptors, and are especially important in the immune system; cytokines modulate the balance between humoral and cell-based immune responses, and they regulate the maturation, growth, and responsiveness of particular cell populations.
Some cytokines enhance or inhibit the action of other cytokines in complex ways.
They are different from hormones, which are also important cell signalling molecules, in that hormones circulate in less variable concentrations and hormones tend to be made by specific kinds of cells.
They are important in health and disease, specifically in host responses to infection, immune responses, inflammation, trauma, sepsis, cancer, and reproduction.
Cytokines are a broad and loose category of small proteins (~5–20 k Da) that are important in cell signalling.
Their release has an effect on the behavior of cells around them.
As of 2008, the current terminology refers to cytokines as immunomodulating agents.
However, more research is needed in this area of defining cytokines and hormones.
The widespread distribution of cellular sources for cytokines may be a feature that differentiates them from hormones.