Abstract | April 5, 2022

Enterotoxigenic Escherichia coli enterotoxins modulate IL-1 signaling and alter mucosal immunity

Presenting Author: Natalya Motyka, MD/PhD Student, 6th Year, Department of Microbiology and Immunology, Tulane University, New Orleans, LA

Coauthors: Sydney Stewart, Research Technician, Microbiology and Immunology, Tulane University, New Orleans, LA; Ian Hollifield, PhD Student, Microbiology and Immunology, Tulane University, New Orleans, LA; Jacob Bitoun, PhD Principal Investigator, Microbiology and Immunology, Tulane University, New Orleans, LA.

Learning Objectives

  1. Identify new roles of IL-1 cytokine signaling following exposure to ETEC enterotoxins;
  2. Understand the interaction between epithelial and innate immune cells following exposure to ETEC enterotoxins.

Background/Knowledge Gap: Enterotoxigenic Escherichia coli (ETEC) are a major cause of diarrheal disease in children younger than 5. Current treatment for ETEC infection is oral rehydration therapy, and there are no licensed vaccines. Insight into preventative or therapeutic mechanisms is imperative, as repeated infections cause physical and mental stunting of children in ETEC-endemic areas. ETEC produce at least one enterotoxin: the heat-labile enterotoxin (LT) and/or the heat-stable enterotoxin (ST), which initiate intracellular signaling cascades via cyclic nucleotides second messengers to cause secretory diarrhea. A lingering question is the evolutionary advantage attained by ETEC strains that produce both ST and LT when either is sufficient to induce diarrhea. We hypothesize that fast-acting ST primes the host for infection by inducing epithelial IL-33, an IL-1 family cytokine, and slower-acting LT sustains IL-33 production but polarizes IL-33 receptor signaling.

Methods: We use in vitro, ex vivo, and in vivo studies to examine responses to ST and LT in epithelial and immune cells at the gene and protein level.

Results: We show that LT induces IL-33 production in T84 cells. LT also induces IL-1Ra, a decoy receptor that prevents IL-1 signaling and suppresses epithelial IL-8 secretion following exposure to IL-1beta. We also show that ST intoxication hastens LT-mediated epithelial transcriptional changes. In wildtype animals, we find that ST- or LT-mediated luminal fluid accumulation coincides with increased IL-33 and IL-1Ra in small intestinal mucosal lysates and IL-33 receptor (IL-33R)-deficient animals are less susceptible to ST-mediated secretion. Once induced, we theorize that IL-33/IL-1Ra signaling modulates the diarrheal response and delays establishment of protective immunity via coordination between epithelial and immune cells. We show that LT suppresses IL-33-induced TNFalpha in BMDCs and BMMs in a cAMP-dependent manner. Additionally, chronic LT intoxication expands hematopoietic CD45+ cells that express IL-33R in small intestinal lamina propria, suggesting that juxtaposition to IL-33-producing epithelial cells is required for expansion of IL-33R+ tissue resident cells.

Conclusions: Our data suggest ST and LT modulate the epithelial contribution to mucosal immunity via IL-33 and IL-1Ra, which now represents a novel target for therapeutics to protect young children from ETEC-mediated secretory diarrhea until immunity develops.

References and Resources:

  1. Qadri F, Akhtar M, Bhuiyan TR, Chowdhury MI, Ahmed T, Rafique TA, Khan A, Rahman SIA, Khanam F, Lundgren A, Wiklund G, Kaim J, Lofstrand M, Carlin N, Bourgeois AL, Maier N, Fix A, Wierzba T, Walker RI, Svennerholm AM. 2020. Safety and immunogenicity of the oral, inactivated, enterotoxigenic Escherichia coli vaccine ETVAX in Bangladeshi children and infants: a double-blind, randomised, placebocontrolled phase 1/2 trial. Lancet Infect Dis 20:208-219.
  2. Harro C, Louis Bourgeois A, Sack D, Walker R, DeNearing B, Brubaker J, Maier N, Fix A, Dally L, Chakraborty S, Clements JD, Saunders I, Darsley MJ. 2019. Live attenuated enterotoxigenic Escherichia coli (ETEC) vaccine with dmLT adjuvant protects human volunteers against virulent experimental ETEC challenge. Vaccine 37:1978-1986.
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