Differential intracellular trafficking of Francisella tularensis strains in human dendritic cells. (56.15)

Abstract F. tularensis, the causative agent of tularemia, is an intracellular pathogen that replicates in macrophages and dendritic cells (DCs), where the bacteria escape the endosomal pathway and replicate in the cytoplasm. DCs act as sentries for the immune system and are often the first cells to engulf invading pathogens and trigger the activation of T-cells. F. tularensis inactivates DCs upon entry, but the mechanism of inactivation is not known. We hypothesize that F. tularensis inactivates DCs by disrupting intracellular trafficking and antigen presentation. Using immunofluorescence microscopy, we have performed a detailed characterization of intracellular trafficking of the F. tularensis laboratory strains Schu S4, LVS and novicida and two clinical type A strains in hDCs. Our data indicates that F. tularensis strains colocalize with EEA-1, LAMP-1 and Rab3 endosomal markers as early as 15 min post infection. In addition, we observe a significantly lower number of pathogenic F. tularensis colocalizing with the above markers than the nonpathogenic F. tularensis LVS and novicida strains. Very few bacteria colocalize with the late lysosomal marker Cathepsin D, and we do not observe differences among strains. These data indicate that pathogenic F. tularensis escape the endosomal pathway in hDCs much more rapidly and in greater numbers than nonpathogenic strains, suggesting that pathogenic F. tularensis actively disrupt intracellular trafficking and subsequent antigen presentation.