Infection of dendritic cells by enterobacteriaceae

Dendritic cells (DC) are potent antigen-presenting cells that play a crucia l role in initiation and modulation of specific immune responses. Various p athogens like viruses or bacteria are able to persist inside DC. In this st udy we investigated the ability of the Gram-Negative bacteria Salmonella ty phimurium and Escherichia coli to infect DC. DC isolated from peripheral bl ood of healthy donors were infected with wildtype S. typhimurium and a nonp athogenic E. coli stool isolate. Association of bacteria with DC was assess ed by labeling of the bacteria with green fluorescent protein. Both Gram-ne gative bacteria were associated with DC as evidenced by microscopy and flow cytometry. The intracellular location could be confirmed by lysis of DC an d subsequent determination of colony-forming units on agar plates, which sh owed a rapid decline in viable Gram-negative bacteria 6 h after infection, being by far more pronounced for E. coli than for S. typhimurium. Testing t he stimulation of T cells by infected versus uninfected but otherwise ident ically treated human immature DC in a mitogen-dependent T cell proliferatio n assay, we found that S. typhimurium, but not E. coli exhibited a suppress ive effect on T cell stimulation, being most significant on days 3-5 after infection. Thus, suppression of dendritic cell function was associated with an enteropathogenic bacterium, S. typhimurium, which can cause severe form s of enteritis. The bacteria with normally mild or no gastric symptoms, E. coli, had no influence on stimulation of T cells by DC.