Elafin is an epithelial proteinase inhibitor also known under various other names such as Skin-derived Anti leukoproteinase (SKALP) and Elastase-Specific Inhibitor (ESI). Elafin belongs to the Trappin gene family and was given the systematic name Trappin-2. The Trappin family is defined by a N-terminal transglutaminase substrate domain and a C-terminal four disulphide core. Trappins have been suggested to play a role in the regulation of inflammation and in protection against tissue damage in stratified epithelia. Elafin is an inhibitor of leukocyte elastase and proteinase-3 and is a substrate for transglutaminases. The protein is constitutively expressed in various epithelia including hair follicles, oesophagus, vagina and oral cavity. Elafin is not present in normal human skin but is strongly induced during inflammation as in psoriasis and wound healing. Antibodies to elafin can be used to evaluate the effects of treatment of psoriasis since its expression is significantly correlated with clinical scores. Antibodies to elafin have also been succesfully used to study differentiation in squamous cell carcinoma of the head-and-neck region, oesophagus and skin. It is also shown that elafin possesses antimicrobial activity against gram-positive and gram-negative bacteria.