Immune responses upon infection of secondary abiotic mice lacking nucleotide-oligomerization-domain-2.

Background: infections are of rising importance worldwide. Given that innate immune receptors including nucleotide-oligomerization-domain-2 (Nod2) are essentially involved in combating enteropathogenic infections, we here surveyed the impact of Nod2 in murine campylobacteriosis.

Methods And Results: In order to overcome physiological colonization resistance preventing from infection, we generated secondary abiotic Nod2 and wildtype (WT) mice by broad-spectrum antibiotic treatment. Mice were then perorally infected with strain 81-176 on 2 consecutive days and could be stably colonized by the pathogen at high loads. Notably, Nod2 deficiency did not affect gastrointestinal colonization properties of . Despite high intestinal pathogenic burdens mice were virtually uncompromised and exhibited fecal blood in single cases only. At day 7 postinfection (p.i.) similar increases in numbers of colonic epithelial apoptotic cells could be observed in mice of either genotype, whereas infected Nod2 mice displayed more distinct regenerative properties in the colon than WT controls. infection was accompanied by increases in distinct immune cell populations such as T lymphocytes and regulatory T cells in mice of either genotype. Increases in T lymphocytes, however, were less pronounced in large intestines of Nod2 mice at day 7 p.i. when compared to WT mice, whereas colonic numbers of B lymphocytes were elevated in WT controls only upon infection. At day 7 p.i., colonic pro-inflammatory mediators including nitric oxide, TNF, IFN-γ and IL-22 increased more distinctly in Nod2 as compared to WT mice, whereas induced IL-23p19 and IL-18 levels were lower in the large intestines of the former. Converse to the colon, however, ileal concentrations of nitric oxide, TNF, IFN-γ, IL-6 and IL-10 were lower in Nod2 as compared to WT mice at day 7 p.i. Even though MUC2 was down-regulated in infected Nod2 mice, this did not result in increased pathogenic translocation from the intestinal tract to extra-intestinal compartments.

Conclusion: In secondary abiotic mice, Nod2 signaling is involved in the orchestrated host immune responses upon infection, but does not control pathogen loads in the gastrointestinal tract.