Role of Salmonella enterica lipopolysaccharide in activation of dendritic cell functions and bacterial containment.

In contrast to nonpathogenic bacteria, the Gram-negative pathogen Salmonella enterica is not eradicated, but persists in murine dendritic cells (DC). The molecular basis of this phenotype is unknown. We set out to characterize bacterial and DC functions that are involved in Salmonella persistence. Our data prove that neither bacterial nor host cell de novo protein biosynthesis is required for Salmonella persistence in DC. We identified the Salmonella O-Ag of the LPS of Salmonella as an important factor for controlling the intracellular fate of Salmonella in DC. A Salmonella strain with entirely absent O-Ag showed an increased rate of uptake by DC, altered intracellular processing, and increased degradation, and also boosted the activation of immune functions of DC. These novel findings demonstrate that in addition to the multiple functions of the bacterial LPS in adaptation to the intestinal environment and protection against innate immune function, this molecule also has an important role in interaction of Salmonella with DC.