The immune system recognizes the presence of pathogens by several proteins that bind to molecules secreted by the pathogen or carried on their surface. The cells responsible for these immune responses include the B-Cells, T-Cells, macrophages, neutrophils ..., basophils, eosinophils, endothelial cells, or mast cells. These cells have distinct roles in the immune system, and communicate with other immune cells by Cytokines, which control proliferation, differentiation and function of cells of the immune system. Furthermore, they are involved in processes of inflammation and in the neuronal, haematopoietic and embryonal development of an organism. Cytokines have been classified on the basis of their biological responses into pro- or anti-inflammatory Cytokines, depending on their effects on immunocytes. Cytokines act in networks or cascades. Many of the Cytokines act locally like autocrine hormones and their targets are cells of the same or similar type as the Cytokine-producing cell. Unlike hormones, Cytokines are not stored in glands as preformed molecules, but are rapidly synthesized and secreted by different cells mostly after stimulation. Cytokines are pleiotropic in their biological activities and play pivotal roles in a variety of responses, including the immune response, hematopoiesis, neurogenesis, embryogenesis, and oncogenesis. They frequently affect the action of other Cytokines in an additive, synergistic or antagonistic manner.
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