Research from Taiyuan Normal University shows that the A and B subunits of heat-labile enterotoxin trigger immune responses through two separate signaling routes—offering a roadmap for safer, more effective vaccine adjuvants
A team of researchers led by Professor Xiaoying Wu has uncovered the long-sought molecular mechanisms by which the A and B subunits of Escherichia coli heat-labile enterotoxin (LT) independently activate immune responses in epithelial cells. Their findings demonstrate that the two subunits—LTA and LTB—trigger inflammation through entirely distinct signaling pathways: LTB via the NF-κB pathway and LTA via the NLRP3 inflammasome pathway. This discovery opens a clear path toward engineering safer, subunit-based mucosal vaccine adjuvants that retain immune-boosting power without the toxicity that has historically limited LT's clinical use.
The team published their findings in Acta Microbiologica Sinica on August 4, 2026.
LT is a potent toxin produced by enterotoxigenic E. coli , a major cause of diarrhea in infants, travelers, and livestock. Despite its toxicity, LT has long been recognized as one of the most powerful known mucosal adjuvants—substances that enhance the body's immune response to vaccines delivered through mucosal surfaces such as the nose, mouth, or gut. However, the inability to separate LT's toxicity from its adjuvant activity has severely hampered its clinical application, most notably after the LT-adjuvanted nasal influenza vaccine Nasalflu was withdrawn following cases of Bell's palsy.
Epithelial cells form the primary physical and immune barrier at mucosal surfaces, yet most previous research on LT adjuvants has focused on professional antigen-presenting cells, which are relatively scarce in mucosal tissues," said Dr. Di Liu, first author of the study and a researcher at the Center for Veterinary Medicine, College of Biological Sciences and Technology, Taiyuan Normal University. "Since the LTB pentamer binds with high affinity to epithelial cell surface receptors, LT is far more likely to interact with epithelial cells than with immune cells when administered via mucosal routes. Understanding what happens inside those epithelial cells is absolutely critical to understanding how LT works as an adjuvant."
The research team prepared biologically active LTB, LTA, and a mutant LTA(R192G) via prokaryotic expression. Using the human small intestinal epithelial cell line FHs 74 Int and a mouse jejunal ex vivo intestinal segment model, they systematically examined cell viability, apoptosis, inflammatory cytokine expression, and changes in the NF-κB and NLRP3 inflammasome pathways.
The results revealed a clear division of labor between the two subunits. LTB primarily induced early apoptosis, significantly upregulated the expression of IL-6, IL-8, IL-1β, and TNF-α, and activated the NF-κB pathway. By contrast, LTA triggered pyroptosis—a highly inflammatory form of programmed cell death—specifically upregulated IL-18 and IL-1β, and activated the NLRP3 inflammasome pathway. The mutant LTA(R192G), which carries a single amino acid substitution that dramatically reduces toxicity, showed weakened effects but could still activate the NLRP3 pathway.
Pyroptosis, the team noted, is not simply cell death—it is a highly immunogenic process that releases a flood of inflammatory signals capable of recruiting and activating immune cells such as dendritic cells, macrophages, and T cells to the site of vaccination. The IL-6 produced in response to LTB promotes B-cell differentiation into plasma cells and drives T-cell proliferation, while the IL-18 induced by LTA stimulates Th1 cells and natural killer cells to produce interferon-γ, enhancing cellular immune responses. Meanwhile, TNF-α from LTB-activated pathways triggers cascading inflammatory signals, and IL-1β from LTA-activated pathways synergistically stimulates T-cell activation and induces other cytokines. Together, these coordinated signals reshape the local immune microenvironment to powerfully amplify responses to co-administered vaccine antigens.
The research team expects their work to accelerate the development of next-generation mucosal vaccines against respiratory and gastrointestinal infectious diseases, as well as pandemic threats. By engineering the LTA and LTB subunits separately—preserving their distinct immunostimulatory pathways while eliminating toxicity—scientists can create adjuvants tailored for vaccines administered through nasal sprays, oral drops, or other mucosal routes.
ACTA MICROBIOLOGICA SINICA
Inflammatory signaling and pyroptosis mediate the mucosal adjuvant effect of Escherichia coli heat-labile enterotoxin subunits
4-Aug-2026