TNF-alpha (Tumor necrosis factor, alpha), a member of the TNF ligand superfamily, is among others, secreted by macrophages, activated monocytes, neutrophils, T-cells, B-cells and natural killer cells stimulated by bacterial lipopolysaccharides. TNF-alpha shows approximately 30% homology with TNF-beta. TNF-alpha plays an important role in the regulation of immune cells. TNF-alpha has many biological activities, including a cytotoxic effect to various tumor cells, causes inflammation, cellular proliferation and plays a critical role in mediating resistance to bacterial infections. Human and murine TNF-alpha show approximately 79% homology and human TNF-alpha is active on murine cells with a slightly reduced specific activity.