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. Unlike hormones, cytokines are not stored in glands as preformed molecules, but are rapidly synthesized and secreted by different cells mostly after stimulation.