Cytokines can be grouped into a family on the basis of sequence, functional and structural similarities.[8][9][10] Tumor necrosis factor (TNF) (also known as TNF alpha or cachectin) is a monocyte-derived cytotoxin that has been implicated in tumour regression, septic shock and cachexia.[2][3] The protein is synthesised as a prohormone with an unusually long and atypical signal sequence, which is absent from the mature secreted cytokine.[4] A short hydrophobic stretch of amino acids serves to anchor the prohormone in lipid bilayers.[5] Both the mature protein and a partially processed form of the hormone are secreted after cleavage of the propeptide.