TNF-alpha is secreted by macrophages, monocytes, neutrophils, T-cells (principally CD4+), and NK-cells. Many transformed cell lines also secrete TNF-alpha. Monomeric human TNF-alpha is a 157 amino acid protein (non-glycosylated) with a reported molecular weight of 17 kD. TNF-alpha forms multimeric complexes; stable trimers are most common in solution. A 26 kD membrane form of TNF-alpha has also been described. TNF-alpha binding to surface receptors elicits a wide array of biologic activities including: cytolysis and cytostasis of many tumor cell lines in vitro, hemorraghic necrosis of tumors in vivo, increased fibroblast proliferation, and enhanced chemotaxis and phagocytosis in neutrophils. The MAb1 antibody can neutralize the bioactivity of natural or recombinant TNF-alpha.