[12]. It is therefore unlikely that the constitutive NKG2D ligand expression is caused by a low-grade inflammatory

activity against the commensal bacteria. The NKG2D ligands were detected using recombinant NKG2D and the specific nature of the NKG2D ligands were investigated by RT-PCR which showed that only Rae-1 had a similar expression pattern as the flow Selleckchem Nutlin 3a cytometry results, whereas H60c merely showed a tendency toward this. Hence, not all NKG2G ligands on IECs seem to be regulated by the gut microbiota. We further found a striking downregulation of IEC NKG2D ligand expression in vancomycin-treated mice, which contradicted the findings in ampicillin-treated and germ-free mice. Vancomycin is a well-known anti-Gram-positive antibiotic but also inhibits many Gram-negative Firmicutes species [36], most likely as a result of an ancient evolutionary co-dependency of certain Gram-positive

and Gram-negative bacteria. However, we previously observed a manyfold increase of A. muciniphila in feces from vancomycin-treated nonobese diabetic mice which constituted almost 90% of the remaining microbiota [35]. This species has been suggested to possess an anti-inflammatory protective effect against inflammatory bowel disease [39], and recent findings in gnotobiotic mice mono-colonized with A. muciniphila suggest a transcriptional host response upon colonization that involves immune tolerance against commensal gut bacteria [40]. selleckchem It is thus tempting to speculate that the dominance of this single species in vancomycin-treated mice is linked to the decreased NKG2D ligand expression on IECs, especially as we found high levels of A. muciniphila in the vancomycin-treated mice which corresponded with low levels of NKG2D ligand expression whereas increased expression of A. muciniphila was not observed

in the ampicillin-treated mice. We also found that dietary XOS propagated A. muciniphila, and in parallel to the data obtain in the vancomycin-treated mice, XOS feeding also caused a marked reduction in the IEC NKG2D ligand expression. The nature and mechanisms behind this interesting correlation, as well as specifying other microbes that may Silibinin modulate NKG2D ligands, need further investigation in, for example gnotobiotic mice. The commensal microbiota can affect NKG2D ligand expression by several different mechanisms, which may not necessarily be mutually exclusive. For instance, the commensal bacteria may establish a regulatory milieu in the intestine, with increased expression of immuno-inhibitory cytokines such as TGF-β and IL-10. In this regard, it is notable that both TGF-β and IL-10 have been shown to downregulate NKG2D ligand surface expression [41, 42]. In agreement with this, IL-10 KO mice were shown to have an increase in IEC NKG2D ligand expression.