Heat-labile enterotoxin (LT) (LT)

Heat-labile enterotoxin (LT) is a major virulence factor produced by enterotoxigenic Escherichia coli (ETEC), a leading cause of traveler's diarrhea and childhood diarrhea in developing countries (StatPearls, 2023). Structurally, LT is an AB5-type toxin consisting of one A subunit with enzymatic activity and five B subunits that mediate binding to GM1 gangliosides on the surface of intestinal epithelial cells (UniProt, P06717). Upon entry into the host cell, the A subunit catalyzes the ADP-ribosylation of the Gs alpha subunit of the heterotrimeric G protein, leading to the constitutive activation of adenylate cyclase and a subsequent surge in intracellular cyclic AMP (cAMP) levels (PubMed, 30241754). This elevation in cAMP triggers the opening of the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channels, resulting in the massive secretion of water and electrolytes into the intestinal lumen, which manifests as watery diarrhea (Nature Reviews Microbiology, 2017). LT is a significant target for vaccine development, with strategies focusing on inactivated whole-cell vaccines or toxoids that elicit neutralizing antibodies against the B subunit (The Lancet Infectious Diseases, 2019). Additionally, LT is being explored as a potent mucosal adjuvant in vaccine formulations due to its ability to enhance immune responses, although safety concerns regarding its inherent toxicity necessitate the use of detoxified mutants (Journal of Immunology Research, 2018). Therapeutic interventions also include the use of oral rehydration therapy to manage the symptoms caused by the toxin's action on the gut (WHO, 2023).

Other names

LT-ILT-IIETEC heat-labile enterotoxinHeat-labile enterotoxin of Escherichia coliLT toxin

Vaccines targeting the heat-labile enterotoxin primarily work by inducing neutralizing antibodies (IgA and IgG) that bind to the B-subunit, preventing the toxin from attaching to GM1 gangliosides on the intestinal epithelium and thereby blocking cellular entry and subsequent toxicity. Experimental small molecule inhibitors aim to competitively bind the B-subunit's sugar-binding sites to prevent host cell attachment.