ABSTRACT
In the late 1970s it became clear that lymphocytes and macrophages mediate a wide variety of actions through the secretion of soluble proteins with hormonal activity. These factors were initially found in crude supernatants of cell cultures include growth factors, lymphokines, interferons, and interleukins and are referred to as cytokines. Subsequent expression of recombinant cytokines allowed a more accurate analysis of their biochemical characteristics and functional properties. Nevertheless, the role of many cytokines in vivo still remains obscure due to the fact that their activities are often pleiotropic in nature and frequently shared with other cytokines.
