Interaction of Listeria monocytogenes with mouse dendritic cells

In this study, the interaction of murine dendritic cells with Listeria monocytogenes was investigated. Dendritic cells are efficient antigen-presenting cells, play a key role in the immune response, and are capable of migrating over substantial distances between sites of infection and lymphoid tissues. L. monocytogenes EGD invaded dendritic cells, escaped from phagosomes into the cytoplasm, and there directed actin nucleation, polymerization, and polarization in a typical fashion, thereby achieving intracellular movement and cell-to-cell spread. The internalization process appears to be independent of the inl locus. Interestingly, an intact microtubular function was essential for efficient uptake, whereas in a previous report, microtubule disruption did not affect bacterial spread in Caco-2 cells. The results obtained also suggest that L. monocytogenes binds to glycosylated receptors of dendritic cells. Uptake of Listeria cells was mediated by a protein kinase-dependent transducing phosphorylation signal that induces the actin polymerization-dependent phagocytic process. To achieve efficient uptake, de novo protein synthesis of eukaryotic and prokaryotic cells is also required. Despite the killing of dendritic cells, wild-type bacteria were found to persist in small numbers in some cells for at least 24 h. When different isogenic mutants of the EGD strain were analyzed for their capability to interact with dendritic cells, it was observed that some virulence-attenuated mutants (i.e., prfA and delta hly) persisted in large numbers for even longer times. Invasion of dendritic cells by L. monocytogenes, which in turn could result in either cell death or persistent infection, might have an important role in the pathogenesis of listeriosis, leading to impaired immune responses with inefficient bacterial clearance and/or promoting bacterial spread.