Intestinal inflammation induced by heat-labile toxin-producing Enterotoxigenic E. Coli infection and impact on immune responses in an experimental human challenge model
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Abstract
Enterotoxigenic Escherichia coli (ETEC) causes significant morbidity, mortality, and growthth faltering among children, particularly in low- and middle-income countries. While gut inflammation contributes to growth faltering, the role of ETEC in inflammation remains poorly understood. We previously demonstrated that ETEC-producing heat-labile toxin (LT) and heat-stable toxins (ST) induced significant inflammation in humans, but LT-only strains are understudied. In this study, we evaluated the intestinal inflammation induced by the LT-only ETEC strain LSN03-016011/A in a human challenge model. Stool samples were analyzed for pre- and post-challenge myeloperoxidase (MPO) and pro and anti-inflammatory cytokines, ETEC shedding, and ETEC-specific antibody responses. MPO, IL-1β, and IL-8 levels significantly increased post-ETEC challenge, but there was no significant difference between symptomatic and asymptomatic participants. Participants protected from severe diarrhea had higher levels of pre-challenge IL-10, IL-13, and IFN-γ compared to those not protected. The MPO and specific cytokine levels were significantly correlated with the seroconversion status to LT and the colonization factor antigen CS17. This study provides evidence that LT-ETEC strain can induce significant intestinal inflammation even in the absence of symptoms, highlighting the need for a vaccine and a better understanding of the impact of ETEC-attributable inflammation on child health in endemic areas.
Author summary
Enterotoxigenic Escherichia coli (ETEC) is one of the leading causes of enteric infections, resulting in diarrhea, malnutrition, and other long-term health effects. However, how ETEC - particularly strains that produce only the heat-labile toxin (LT) - can contribute to gut inflammation is not fully understood. In this study, we examined the impact of an LT-ETEC infection on gut inflammation and its relations to ETEC-specific immune responses using samples from participants in a controlled human infection study. We found that LT-ETEC induces a significant level of gut inflammation marker myeloperoxidase (MPO) and pro-inflammatory cytokines IL-8 and IL-1β, when the patients had moderate to severe diarrhea and even when diarrheal symptoms were mild or absent. Gut inflammation level correlated with immune responses to ETEC. These findings suggest that LT-ETEC infection causes significant gut inflammation, which plays a role in immune responses. Our results highlight the need for preventive strategies to reduce the burden of ETEC-related illness, particularly in regions where these infections are common, to prevent broader adverse consequences for gut health and child development.
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This Zenodo record is a permanently preserved version of a PREreview. You can view the complete PREreview at https://prereview.org/reviews/15299669.
Overall Assessment:
This study investigated how infection with a heat-labile toxin-only strain of Enterotoxigenic Escherichia coli (ETEC) affects intestinal inflammation and immune responses in humans. Fifteen healthy adults were intentionally exposed to the LT-only ETEC strain LSN03-016011/A, and their stool and blood samples were collected before and after infection. The researchers found significant increases in fecal myeloperoxidase (MPO), IL-1β, and IL-8 levels following the challenge, even among participants who did not develop severe diarrhea. Also, participants who did not develop moderate to severe diarrhea had higher levels of IL-10, IL-13, and IFN-γ before being exposed to the …
This Zenodo record is a permanently preserved version of a PREreview. You can view the complete PREreview at https://prereview.org/reviews/15299669.
Overall Assessment:
This study investigated how infection with a heat-labile toxin-only strain of Enterotoxigenic Escherichia coli (ETEC) affects intestinal inflammation and immune responses in humans. Fifteen healthy adults were intentionally exposed to the LT-only ETEC strain LSN03-016011/A, and their stool and blood samples were collected before and after infection. The researchers found significant increases in fecal myeloperoxidase (MPO), IL-1β, and IL-8 levels following the challenge, even among participants who did not develop severe diarrhea. Also, participants who did not develop moderate to severe diarrhea had higher levels of IL-10, IL-13, and IFN-γ before being exposed to the bacterial strain. Intestinal inflammation was found to be correlated with stronger immune responses to ETEC antigens CS17 and CTB. It was also found that having only LT (heat-labile toxin) was enough to cause strong inflammation, and adding ST (heat-stable toxin) didn't necessarily make the inflammation worse in this study. However, no strong link was found between inflammation and ETEC shedding in stool, meaning the amount of bacteria in stool and level of gut inflammation had no correlation. The findings suggest that there was no strong link found between the amount of bacteria one had in their body and the degree of infection and inflammation found.
Major Strengths:
Novelty in LT-only ETEC strains: This study addresses a significant knowledge gap within LT-only ETEC strains since most research on ETEC inflammation is focused on strains producing both heat-labile (LT) and heat-stable (ST) toxins.
High internal validity: Using a controlled human infection model allowed the researchers to directly link infection to changes in inflammation and immune responses. Controlled exposure of healthy volunteers to a known amount of ETEC bacteria removes any confounding factors that might be present in real-world observational studies.
High reliability: By using a comprehensive biomarker and immune response assessment that measured factors more than diarrhea symptoms like inflammatory markers, cytokines, ETEC shedding, and antibody responses, this increased the reliability of the study by making their findings less likely to be due to chance.
Major Concerns:
Small sample size and statistical power: Since there were only 15 people in the study (most likely due to the extensive biomarker assessments needed and the fact that it was a controlled human infection model), this diminishes the high reliability that was initially considered a major strength
Possible false statistical significance: By not correcting for multiple comparisons, the study may have overstated the number of statistically significant findings since they ran over 50 different tests comparing biomarkers, cytokines, immune responses, etc., and should interpret any results with caution.
No Control for Baseline Variability: Because they only measured each person's baseline once, they might have misjudged how much true change happened after infection. Natural day-to-day variation within biomarkers has the potential to change the effects of infection.
Minor Concerns:
Biomarker Measurement Clarity: The lack of clarity in methods for measuring fecal biomarker concentrations would help create reproducible results.
Figures and Statistical Presentation: Figure 6 does not seem to have a clear pattern to where the significant stars are applied (*). For example, some similar-looking differences are labeled as significant while some are not. Additionally, sample sizes for groups are not always labeled clearly on figures and tables.
Recommendations:
Apply Corrections for Multiple Comparisons: In order to correct for multiple comparisons and decrease the chances of false positive, applying a false discovery rate (FDR) correction (ex/ Benjamini-Hochberg) to adjust p-values across groups of cytokine changes or biomarker correlations would be best.
Strengthen Baseline Measurements: Use more than one baseline measurement since biomarker variability is common. Collecting multiple pre-infection samples (for example, 2–3 days before infection) and an average or median of them to define a more stable baseline is recommended.
Increase Sample Size and Statistical Power: Recreating or redoing the study with a substantially larger population size of healthy volunteers would increase the validity and generalizability of this study.
Conclusion:
This preprint shows that LT-only ETEC infections can cause significant intestinal inflammation even without obvious physical symptoms. By using a carefully controlled human challenge model and inflammatory biomarkers, this study emphasizes that LT-only strains deserve greater recognition in public health strategies and vaccine development. ETEC infections on child health have a vast global impact, especially in third-world countries. The findings of this study should be brought to researchers' awareness in order to enhance diagnostic awareness and reduce long-term consequences of ETEC-related gut damage in order to create a more equitable and healthy world.
Competing interests
The author declares that they have no competing interests.
Use of Artificial Intelligence (AI)
The author declares that they used generative AI to come up with new ideas for their review.
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This Zenodo record is a permanently preserved version of a PREreview. You can view the complete PREreview at https://prereview.org/reviews/15299690.
Overall Assessment:
This study investigated how infection with a heat-labile toxin-only strain of Enterotoxigenic Escherichia coli (ETEC) affects intestinal inflammation and immune responses in humans. Fifteen healthy adults were intentionally exposed to the LT-only ETEC strain LSN03-016011/A, and their stool and blood samples were collected before and after infection. The researchers found significant increases in fecal myeloperoxidase (MPO), IL-1β, and IL-8 levels following the challenge, even among participants who did not develop severe diarrhea. Also, participants who did not develop moderate to severe diarrhea had higher levels of IL-10, IL-13, and IFN-γ before being exposed to the …
This Zenodo record is a permanently preserved version of a PREreview. You can view the complete PREreview at https://prereview.org/reviews/15299690.
Overall Assessment:
This study investigated how infection with a heat-labile toxin-only strain of Enterotoxigenic Escherichia coli (ETEC) affects intestinal inflammation and immune responses in humans. Fifteen healthy adults were intentionally exposed to the LT-only ETEC strain LSN03-016011/A, and their stool and blood samples were collected before and after infection. The researchers found significant increases in fecal myeloperoxidase (MPO), IL-1β, and IL-8 levels following the challenge, even among participants who did not develop severe diarrhea. Also, participants who did not develop moderate to severe diarrhea had higher levels of IL-10, IL-13, and IFN-γ before being exposed to the bacterial strain. Intestinal inflammation was found to be correlated with stronger immune responses to ETEC antigens CS17 and CTB. It was also found that having only LT (heat-labile toxin) was enough to cause strong inflammation, and adding ST (heat-stable toxin) didn't necessarily make the inflammation worse in this study. However, no strong link was found between inflammation and ETEC shedding in stool, meaning the amount of bacteria in stool and level of gut inflammation had no correlation. The findings suggest that there was no strong link found between the amount of bacteria one had in their body and the degree of infection and inflammation found.
Major Strengths:
Novelty in LT-only ETEC strains: This study addresses a significant knowledge gap within LT-only ETEC strains since most research on ETEC inflammation is focused on strains producing both heat-labile (LT) and heat-stable (ST) toxins.
High internal validity: Using a controlled human infection model allowed the researchers to directly link infection to changes in inflammation and immune responses. Controlled exposure of healthy volunteers to a known amount of ETEC bacteria removes any confounding factors that might be present in real-world observational studies.
High reliability: By using a comprehensive biomarker and immune response assessment that measured factors more than diarrhea symptoms like inflammatory markers, cytokines, ETEC shedding, and antibody responses, this increased the reliability of the study by making their findings less likely to be due to chance.
Major Concerns:
Small sample size and statistical power: Since there were only 15 people in the study (most likely due to the extensive biomarker assessments needed and the fact that it was a controlled human infection model), this diminishes the high reliability that was initially considered a major strength
Possible false statistical significance: By not correcting for multiple comparisons, the study may have overstated the number of statistically significant findings since they ran over 50 different tests comparing biomarkers, cytokines, immune responses, etc., and should interpret any results with caution.
No Control for Baseline Variability: Because they only measured each person's baseline once, they might have misjudged how much true change happened after infection. Natural day-to-day variation within biomarkers has the potential to change the effects of infection.
Minor Concerns:
Biomarker Measurement Clarity: The lack of clarity in methods for measuring fecal biomarker concentrations would help create reproducible results.
Figures and Statistical Presentation: Figure 6 does not seem to have a clear pattern to where the significant stars are applied (*). For example, some similar-looking differences are labeled as significant while some are not. Additionally, sample sizes for groups are not always labeled clearly on figures and tables.
Recommendations:
Apply Corrections for Multiple Comparisons: In order to correct for multiple comparisons and decrease the chances of false positive, applying a false discovery rate (FDR) correction (ex/ Benjamini-Hochberg) to adjust p-values across groups of cytokine changes or biomarker correlations would be best.
Strengthen Baseline Measurements: Use more than one baseline measurement since biomarker variability is common. Collecting multiple pre-infection samples (for example, 2–3 days before infection) and an average or median of them to define a more stable baseline is recommended.
Increase Sample Size and Statistical Power: Recreating or redoing the study with a substantially larger population size of healthy volunteers would increase the validity and generalizability of this study.
Conclusion:
This preprint shows that LT-only ETEC infections can cause significant intestinal inflammation even without obvious physical symptoms. By using a carefully controlled human challenge model and inflammatory biomarkers, this study emphasizes that LT-only strains deserve greater recognition in public health strategies and vaccine development. ETEC infections on child health have a vast global impact, especially in third-world countries. The findings of this study should be brought to researchers' awareness in order to enhance diagnostic awareness and reduce long-term consequences of ETEC-related gut damage in order to create a more equitable and healthy world.
Competing interests
The author declares that they have no competing interests.
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