Heat-labile enterotoxin

Heat-labile enterotoxin is a type of labile toxin found in Escherichia coli and Bacillus cereus.

Escherichia coli

The heat labile enterotoxin is inactivated at high temperatures.^[1][2]

It acts similarly to the cholera toxin by raising cAMP levels through ADP-ribosylation of the alpha-subunit of a Gs protein leading to the constitutive activation of adenylate cyclase. Elevated cAMP levels stimulate the activation of the CFTR channel thus stimulating secretion of Chloride ions and water from the enterocyte into the gut lumen. This ionic imbalance causes watery diarrhea.

In addition to its effects on chloride secretion, which involve the same steps as the effects of cholera toxin, heat-labile enterotoxin binds additional substrates: lipopolysaccharide on the surface of E. coli cells and A-type blood antigens.^[3] The importance of these binding events is not yet known.

References

1. Wagner B, Hufnagl K, Radauer C, et al. (April 2004). "Expression of the B subunit of the heat-labile enterotoxin of Escherichia coli in tobacco mosaic virus-infected Nicotiana benthamiana plants and its characterization as mucosal immunogen and adjuvant". Journal of Immunological Methods. 287 (1-2): 203–15. doi:10.1016/j.jim.2004.02.001. PMID 15099768.
2. Glenn GM, Flyer DC, Ellingsworth LR, et al. (October 2007). "Transcutaneous immunization with heat-labile enterotoxin: development of a needle-free vaccine patch". Expert Rev Vaccines. 6 (5): 809–19. doi:10.1586/14760584.6.5.809. PMID 17931160.
3. Mudrak B and Kuehn MJ (2010). "Heat-labile enterotoxin: Beyond GM1 binding". Toxins. 2 (6): 1445–1470. doi:10.3390/toxins2061445.