Cytokines, small proteins (about 5-20 kDa), are very important in human health and disease, specifically in host responses to infection, immune responses, inflammation, trauma, sepsis, cancer, and reproduction. Similar to hormones, cytokines are important in cell signaling: released by certain types of cells, they affect the behavior of other cells and sometimes the releasing cell itself. Different from hormones, cytokines circulate in much higher concentrations and are produced by various types of cells, such as immune cells like macrophages, B lymphocytes, T lymphocytes and mast cells, endothelial cells, fibroblasts, and stromal cells. More than one type of cells may produce the same cytokine. Cytokines act through receptors to modulate the balance between humoral and cell-based immune responses. Cytokines regulate the maturation, growth, and responsiveness of particular cell populations. Some cytokines enhance or inhibit the action of other cytokines in complex ways.
Cytokines can be classed as the following based on their presumed functions, cell of secretion, or target of action:
Interleukins – produced mainly by T-helper cells.
Chemokines – mediating chemoattraction (chemotaxis) between cells.
Lymphokines – produced by lymphocytes.
Monokines – produced primarily by monocytes and macrophages.
Interferons – involved in antiviral responses.
Colony stimulating factors – supporting the growth of cells in semisolid media.
Type I (grouped by receptor subunit):
Interferon II subfamily:
IL 17 family:
CCL2 / MCP-1
CCL3 / MIP-1α
CCL4 / MIP-1β
CCL5 / RANTES
CCL18 / PARC / DC-CK1 / AMAC-1 / MIP-4