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

Background: Campylobacter jejuni 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 C. jejuni infection, we generated secondary abiotic Nod2(-/-) and wildtype (WT) mice by broad-spectrum antibiotic treatment. Mice were then perorally infected with C. jejuni 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 C. jejuni. 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 C. jejuni infected Nod2(-/-) mice displayed more distinct regenerative properties in the colon than WT controls. C. jejuni 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 C. jejuni infection. At day 7 p.i. colonic pro-inflammatory mediators including nitric oxide, TNF, IFN-gamma and IL-22 increased more distinctly in Nod2(-/-) as compared to WT mice, whereas C. jejuni 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-gamma, 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 C. jejuni 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 C. jejuni infection, but does not control pathogen loads in the gastrointestinal tract.