Endotoxins

Definition

Toxic components of the outer cell envelope of Gram-negative bacteria, most commonly lipopolysaccharides (LPS), that are released upon cell lysis and trigger strong innate immune responses in hosts. In arthropod biology, endotoxins are relevant as virulence factors of entomopathogenic bacteria and as immune modulators in vector-pathogen interactions.

Etymology

Example

The delta endotoxins (Cry proteins) produced by Bacillus thuringiensis form crystalline inclusions that, when ingested by lepidopteran larvae, solubilize in the alkaline midgut and create pores in epithelial cells, causing gut paralysis and death—forming the basis of Bt insecticides and transgenic Bt crops.

Synonyms

• LPS
• lipopolysaccharide

Related Terms

• Exotoxins
• lipopolysaccharide
• innate immunity
• entomopathogenic bacteria
• Bacillus thuringiensis
• septic shock
• Gram-negative bacteria

Usage Notes

In strict modern usage, 'endotoxin' is often treated as synonymous with lipopolysaccharide (LPS), though this conflation is imprecise: endotoxins are structurally defined by their cell-envelope location and release upon cell death, while LPS is a specific molecular class. The term 'endotoxin' contrasts with 'exotoxin,' which refers to secreted toxic proteins. In entomology, the notable exception is the delta endotoxin of B. thuringiensis, which is a protein crystal rather than LPS and is released by cell lysis rather than secretion, justifying its endotoxin classification by mechanism rather than chemistry.