Cytokines and Growth Factors
Cytokines and growth factors are signaling molecules that control the activities of cells through intercellular communication. Numerous families of diverse molecules are categorized as cytokines and/or growth factors. Members of these families bind to specific receptors on the surface of their target cells and induce intracellular signaling pathways that regulate an array of biological processes such as cell proliferation, activation, differentiation, and migration. Cytokines are secreted by a variety of cells but particularly by cells of the immune system. Cytokines produced by these cells are essential for initiating inflammation and the innate and adaptive immune response following infection or injury. Cytokine signaling can induce both local and systemic effects and the outcome is frequently determined by the combination of cytokines that are present. Growth factors are also secreted by a number of different cell types. They regulate multiple processes during development including cell proliferation, differentiation, tissue organization, morphogenesis, and angiogenesis. In addition, they are involved in regulating metabolism, wound healing, and maintaining tissue homeostasis in adult organisms. Constitutive activation of growth factor signaling is frequently associated with cellular transformation and tumorigenesis.