The gastrointestinal microbiota is initially acquired during birth and evolves throughout the postnatal period reaching a mature microbial community (i.e., composition and abundance) over time. In this regard, few studies have evaluated the impact of neonatal colonization by a pathobiont on the vertical transmissibility of the microbiota or subsequent sensitivity to colitic insults. LF82 is an adherent invasive E. coli (AIEC) strain that has been associated with ileal Crohn's disease. The aim of this study was to evaluate changes in the microbiota and in the sensitivity to dextran sodium sulfate (DSS)-induced colitis following colonization with LF82 as an adult or neonate by vertical acquisition or gavage in gnotobiotic C3H/HeN:TAC mice harboring the altered Schaedler flora (ASF). We hypothesized that ASF mice colonized with LF82 as a neonate would be less susceptible to DSS-induced inflammation compared to ASF mice colonized with LF82 as young adults.Methods:
Adult ASF mice were colonized with LF82 by oral gavage (Generation 0, G0) and bred to produce G1 mice colonized with LF82 from birth. Additionally, neonatal mice were colonized with LF82 by gavage at less than 24 hours of age (G0Neo). To trigger colitis, G1, G0Neo, and G0 mice were given 2.0% DSS in drinking water for 7 days. At necropsy, colonic tissues, serum, and mesenteric lymph nodes (MLN) were harvested to evaluate the severity of intestinal inflammation and magnitude of immunologic responses. DNA extracted from cecal contents was used to assess microbial abundance.Results:
More severe macroscopic and histologic inflammation was present in the G1 + DSS and G0Neo + DSS mice when compared to G0 + DSS mice. The lesions in the G1 + DSS mice were characterized by marked ulceration, inflammatory cell infiltrate, glandular hyperplasia and stromal collapse, and was diffuse and transmural in most of the G1 + DSS mice. In the severely diseased G1 + DSS mice, colitis was accompanied by elevated levels of IFNγ and IL-17 secreted from colonic explants. RNAscope evaluation demonstrated the presence of CD4+ T cells expressing IFNγ or IL-17 demonstrating the cellular source of these cytokines. RNAseq analysis also demonstrated differential inflammatory gene expression between treatment groups. Ex vivo stimulation of MLN-derived CD4+ T cells revealed differential ASF antigen-specific proliferation. Based on 16s rRNA gene sequence taxonomic profiling, colonization of the ASF mice with LF82 minimally altered the composition of the microbial community at 10 to 12 weeks of age.Conclusions:
We demonstrated that neonatal colonization of ASF mice with LF82 resulted in the development of more severe DSS-induced colitis as compared to adult mice colonized with LF82. LF82 did not significantly impact the microbial community (i.e., abundance) but triggered altered immune responses characterized by a prominent Th17 response and differential immunoreactivity to ASF antigens. These data suggest that the age at which an individual is colonized by an AIEC pathobiont will differentially affect the host's mucosal immune response and impact the host's susceptibility to subsequent inflammatory insults.