Heat labile enterotoxin (LT) is produced by Entero Toxigenic E. coli.and is similar to cholera toxin (CT). The identity of the amino acid sequences of LT and CT is about 80% and both toxins are consist of one subunit A and five subunit B. LT continuously activates adenylate cyclase and elevated level of cAMP inhibits absorption of sodium ions by intestinal villi cells, and stimulates secretion of Cl- by villi and crypt cells, thus causing diarrhea. It works as a potent mucosal adjuvant and is considered to be used as adjuvant with vaccines. Subunit A possesses signal peptide of the amino acids 1-18, and the mature form consists of 19-258 amino acids. Subunit B has signal peptide of 1-21, and the mature form consists of 22-124 amino acids.