The monoclonal antibody 52B83 reacts with tumor necrosis factor alpha (TNF-alpha). TNF-alpha is a homotrimeric 17 kDa protein, that interacts with either one of the two types of TNF-receptors, termed I and II, leading to receptor cross-linking and signal transduction. The receptors differ strongly in their intra-cellular signaling pathways.TNF-alpha was originally described as a highly cytotoxic cytokine for tumor cells, it causes tumor necrosis in vivo and shows cytolytic activity against tumor cells in vitro. Furthermore,- TNF-alpha is found to be a central mediator in many inflammatory and immunological processes. It can be induced by various products of micro-organisms and by various cytokines leading to expression of a wide variety of- cytokines. The pro-inflammatory properties of- TNF-alpha play a central role in several auto-immune diseases such as rheumatoid arthritis and inhibition by neutralizing molecules have been shown to be beneficial in patients.