Intestinal and systemic inflammation induced by symptomatic and asymptomatic enterotoxigenic E. coli infection and impact on intestinal colonization and ETEC specific immune responses in an experimental human challenge model

Abstract

Recent studies have gained a better appreciation of the potential impacts of enteric infections beyond symptomatic diarrhea. It is recognized that infections by several enteropathogens could be associated with growth deficits in children and intestinal and systemic inflammation may play an important underlying role. With enterotoxigenic E. coli (ETEC) being one of the leading causes of diarrhea among children in the developing world and important contributor to stunting, a better understanding of the impact of ETEC infection beyond diarrhea is timely and greatly needed. To address this, we evaluated if ETEC infection induces intestinal and systemic inflammation and its impact on colonization and immune responses to ETEC vaccine-specific antigens in a dose descending experimental human challenge model using ETEC strain H10407. This study demonstrates that the concentrations of myeloperoxidase (MPO) in stool and intestinal fatty acid-binding protein (an indicator of compromised intestinal epithelial integrity) in serum, significantly increased following ETEC infection in both diarrhea and asymptomatic cases and the magnitudes and kinetics of MPO are dose and clinical outcome dependent. Cytokines IL-17A and IFN-γ were significantly increased in serum post-ETEC challenge. In addition, higher pre-challenge concentrations of cytokines IL-10 and GM-CSF were associated with protection from ETEC diarrhea. Interestingly, higher MPO concentrations were associated with higher intestinal colonization of ETEC and lower seroconversions of colonization factor I antigen, but the reverse was noted for seroconversions to heat-labile toxin B-subunit. Together this study has important implications for understanding the acute and long-term negative health outcomes associated with ETEC infection.

Keywords: ETEC; cytokines; immune response; intestinal fatty acid-binding protein; intestinal inflammation; myeloperoxidase; systemic inflammation.

Figure 1.

MPO concentrations pre- and post ETEC challenge

Figure 2.

Pre-challenge MPO concentration in the subjects who did versus who did not seroconverted following challenge. Upper panel CFA/I, lower panel LTB; A,D: serum IgA, B,E: Serum IgG; C,F: ALS IgA. SC: seroconverted, NSC: not seroconverted; Box plot showing Min, Max and Median. p < .05:*; p < .01:**

Figure 3.

I-FABP concentrations pre- and post ETEC challenge

Figure 4.

IL-17A concentrations pre- and post ETEC challenge. A. Magnitudes and kinetics of IL-17A concentrations by clinical outcome. MSD: moderate to severe diarrhea; ND: no diarrhea; D0: day before challenge; −8: 8 hours after challenge; 1 to 9: 1 to 9 days after challenge. B. Comparisons of the peak IL-17A concentrations on any day among the subjects with MSD and ND. D0: day before challenge; Peak: highest concentrations of IL-17A. Box plot showing Min, Max and Median. p < .01:**. Rx: Antibiotic treatment

Figure 5.

IFN-γ concentrations pre and post ETEC challenge.A. Magnitudes and kinetics of IFN-γ concentrations by clinical outcome. MSD: moderate to severe diarrhea; ND: no diarrhea; D0: day before challenge; D1-8: 8 hours after challenge; D1 to D9: 1 to 9 days after challenge. B. Comparisons of the peak IFN-γ concentrations on any day among the subjects with MSD and ND. D0: day before challenge; Peak: highest concentrations of IFN-γ. Box plot showing Min, Max and Median. p < .01:**. Rx: Antibiotic treatment

Figure 6.

Pre-challenge concentrations of GM-CSF and IL-10 among the subjects with MSD or ND. MSD: moderate to severe diarrhea; ND: no diarrhea; Box plot showing Min, Max and Median. p = <0.01: **; p = <0.001: ***