Escherichia coli heat labile enterotoxin (LT) is regarded as a potent mucosal virulence factor. It shows an immune modulatory activity to increase immune responses to other antigens on mucosal surfaces. LT forms an $AB_5$ toxin structure composed of one A subunit and a pentamer of five B subunits. Because the A subunit is responsible for the enzymatic activity and toxicity, the B subunits have been extensively studied for their exploitation as adjuvants. Having the ability to bind TLR as well as ganglioside receptors, the B subunits of LT shows adjuvanticity. In practice, they are under study concerning the immune modulatory effects for vaccines.