Cytokines are immuno-modulating cell signalling molecules. They are low-weight molecular proteins that mediate their effects when they bind to specific cell surface receptors.
On binding to a receptor, a cytokine stimulates the receptor to send a signal to the cell that alters its function or phenotype. The cytokines can trigger the up regulation or down regulation of several genes and their transcription factors which may lead to the formation of other cytokines and new cell surface receptors, or it may suppress the cytokine's effect through negative feedback. In this way, cytokines can regulate the intensity and duration of the immune system responses.
Cellular response to cytokines
Cells have different responses to certain cytokines, depending on the following:
The presence of the cytokine receptor on the cell surface
The abundance of the receptor on the cell surface
The abundance of the cytokine in the environment outside the cell
The ability of the cytokine to initiate the downstream signal within the cell on binding to the cell surface receptor
Some cytokines share similar functions. Cytokine actions may be autocrine meaning the cytokine acts on the same cell that secretes it. If the cytokine acts on cells nearby other than the one that secreted it, the action is termed paracrine. If the cytokines travel through the circulation and target cells in other parts of the body, the action is described as endocrine.
Some of the general functions of cytokines include:
Regulation of metabolic pathways within cells of muscle, adipose tissue, central nervous system, and liver.