Rat tumor necrosis factor-alpha
Rat tumor necrosis factor-alpha (TNF-α) is primarily a homotrimeric 17 kDa protein, a potent mediator of inflammatory and metabolic functions. Originally known as a highly cytotoxic cytokine for tumor cells, it is produced by lipopolysaccharide stimulated macrophages. When injected into tumor bearing animal, it causes tumor necrosis in vivo and shows cytolytic activity against tumor cells in vitro. Further, TNF-α has been implied as central mediator in shock induced by gram negative microorganisms. TNF-α functions as a central mediator in many inflammatory and immunological processes. Interestingly, it also induced on its turn the production of many cytokines. Signal transduction occurs via two types of TNF-receptors, the p55 and p75 TNF-receptors. The receptors differ strongly in their intracellular signaling pathways.