Human dendritic cells infected by Listeria monocytogenes: induction of maturation, requirements for phagolysosomal escape and antigen presentation capacity

An important feature of microbial infections is the ability of the microorg anisms to interfere with and modulate the induction of host immune reaction s. However, little is known about the effects of broad host range pathogens such as Listeria monocytogenes on similar cell types in different hosts. H ere we examine the effects of the human and animal pathogen L. monocytogene s on human dendritic cells (DC) since this type of cells is essential for t he initiation of immune responses. Listeria are phagocytosed efficiently by immature human DC and the bacteria escape from the phagolysosome quickly. Lack of the pore-forming activity of listeriolysin, which was found to be e ssential for the vacuolar escape of this bacterium in other cell types, ret arded but did not prevent egress from the vacuole. Treatment of cultures of immature DC with L. monocytogenes resulted in rapid changes in morphology and cellular constitution followed by maturation of the DC. This could be j udged by the appearance of maturation-specific cell surface markers. Antige n presentation to CD4 T cells was apparently not impaired by the infection. These results are in clear contrast to results obtained previously in the mouse system (Guzman et al., Mel. Microbiol. 1996. 20: 119-126; Darji et al ., Eur. J. Immunol. 1997. 27: 1696-1703.).