C57-CD40 ligand deficient mice: A potential model for enterotoxigenic Escherichia coli (H10407) colonization

Enterotoxigenic Escherichia coli (ETEC) are a major cause of diarrheal disease in humans, calves and pigs. In humans, these infections mainly occur in developing countries leading to a high diarrheal morbidity and infant mortality and to travellers' diarrhea. ETEC strains constitute a phenotypically and genetically diverse pathotype with as common characteristics the production of heat-labile (LT) and/or heat-stable enterotoxins (ST) as well as of one or more fimbrial colonization factors. Despite the global importance of these pathogens, a broadly ETEC protective vaccine is not yet available, partially due to the lack of a suitable animal model for human ETEC. Such model would allow to test more ETEC molecules as potential vaccine candidates. The C57-CD40 ligand deficient (C57-cd40l^-/-) mouse has been successfully used to develop infection models of intestinal pathogens, but little is known about its humoral immune response. Therefore, the aims of this study were to characterize the humoral immune response of C57 and C57-cd40l^-/- mice and to determine the persistence of ETEC H10407 and two of its variants after oral inoculation. The serum IgM, IgG and IgA and faecal IgG and IgA concentrations, of twelve mice per mouse strain (C57 and C57-cd40l^-/-), were determined by ELISA. All serum immunoglobulins and the faecal IgG concentration were significantly lower in C57-cd40l^-/- than in C57 mice. In contrast the faecal IgA concentration was significantly higher in the C57-cd40l^-/- mice. This high intestinal IgA concentration might be a compensatory T cell-independent production of IgA production. Both mouse strains were orally inoculated with 5×10⁸ ETEC H10407 (LT⁺, ST-colonization factor antigen I (CFA/I)⁺) and ETEC in animal faeces was established by culture followed by st and lt loci identification by PCR until day 14 post infection. Most C57 mice eliminated the strain within 3 days whereas infection remained in C57-cd40l^-/- mice until day 14. Subsequently both mouse strains were inoculated with ETEC H10407 variants and followed up until day 113. Likewise C57 mice eliminated both ETEC variants within 4 days. All C57-cd40l^-/- mice had eliminated the LT^- variant at day 31, whereas the ST-CFA/I^- variant remained in mice stools until day 113. These observations suggest that C57-cd40l^-/- mice are permissive for ETEC H10407 colonization.