Low doses of diarrhoeagenic E. coli induce enhanced monocyte and mDC responses and prevent development of symptoms after homologous rechallenge

Abstract

The experimental challenge with attenuated enterotoxigenic E. coli strain E1392/75-2A prevents diarrhea upon a secondary challenge with the same bacteria. A dose-response pilot study was performed to investigate which immunological factors are associated with this protection. Healthy subjects were inoculated with increasing E. coli doses of 1E6-1E10 CFU, and three weeks later, all participants were rechallenged with the highest dose (1E10 CFU). Gastrointestinal discomfort symptoms were recorded, and stool and blood samples were analyzed. After the primary challenge, stool frequency, diarrhea symptom scores, and E. coli-specific serum IgG (IgG-CFA/II) titer increased in a dose-dependent manner. Fecal calprotectin and serum IgG-CFA/II response after primary challenge were delayed in the lower dose groups. Even though stool frequency after the secondary challenge was inversely related to the primary inoculation dose, all E. coli doses protected against clinical symptoms upon rechallenge. Ex vivo stimulation of PBMCs with E. coli just before the second challenge resulted in increased numbers of IL-6+/TNF-α+ monocytes and mDCs than before the primary challenge, without dose-dependency. These data demonstrate that primary E. coli infection with as few as 1E6 CFU protects against a high-dose secondary challenge with a homologous attenuated strain. Increased serum IgG-CFA/II levels and E. coli-induced mDC and monocyte responses after primary challenge suggest that protection against secondary E. coli challenges is associated with adaptive as well as innate immune responses.

Dietary Intervention with Whey Protein Concentrate Does Not Affect Toll-like Receptor Responses and Gene Expression Patterns in Peripheral Blood Mononuclear Cells of Healthy Volunteers

“…We recently demonstrated that a primary in vivo challenge of healthy volunteers with diarrheagenic E. coli bacteria strain E1392/75-2A at doses as low as 1E6 CFU resulted in protection against secondary infection three weeks later [ 27 ]. The primary infection primed monocytes and mDCs for an increased IL-6 and TNF-α production after restimulation with E. coli or TLR ligands ex vivo .…”