Tumor Necrosis Factor alpha (TNF-alpha) is a 17.3kD multi-functional pro-inflammatory cytokine primarily secreted by macrophages, but also produced by T and B lymphocytes, activated monocytes and fibroblasts. TNF-alpha exists in both a transmembrane and mature soluble form and has many biological properties, including activation of transcription factor NF-KappaB, the induction of apoptosis in various tumor cell lines and the stimulation of cell differentiation and proliferation under certain conditions. Studies have revealed a role for TNF-alpha in inflammation, septic shock, autoimmune disease and rheumatoid arthritis.