Cytokines and chemokines are both small proteins made by cells in the immune system. They are important in the production and growth of lymphocytes, and in regulating responses to infection or injury such as inflammation and wound healing. Cytokines are the general category of messenger molecules, while chemokines are a special type of cytokine that direct the migration (chemotaxis) of white blood cells to infected or damaged tissues. Unlike most other cytokines, chemokines regulate their action through interactions with seven-transmembrane, rhodopsin-like G protein-coupled receptors (GPCRs). Cytokines are secreted in the mammalian immune system, and used as messenger molecules to control the duration and strength of the immune response to foreign microorganisms. Many cytokines produced by T cells direct the immune response of various white blood cells (leukocytes) to a foreign microorganism in the body. Among the important varieties are the interleukin (IL) molecules and interferon alpha and beta. The ILs help regulate inflammation, fever, and wound healing, among other things, while the interferons block the replication of viruses. As part of the superfamily of cytokine receptors belongs to the large family of GPCR receptors (GPCR-A1 and A2), among which the CCR and CXC type chemokine receptors, Axon Ligands™ that interact with these receptors have thus been listed in the corresponding sections of the GPCR receptors as well. Additionally, the superfamily of cytokine receptors differentiates tumor necrosis factor (TNF) type receptors and interleukin (IL) type receptors, and a small sub-family of other cytokine receptors that do not fit into the previously lised subfamilies, based on either structure or function.