In vivo activation of dendritic cells and T cells during Salmonella enterica serovar typhimurium infection

The present study was initiated to gain insight into the interaction betwee n splenic dendritic cells (DC) and Salmonella enterica serovar Typhimurium in vivo. Splenic phagocytic cell populations associated with green fluoresc ent protein (GFP)-expressing bacteria and the bacterium-specific T-cell res ponse were evaluated in mice given S. enterica serovar Typhimurium expressi ng GFP and ovalbumin. Flow cytometry analysis revealed that GFP-positive sp lenic DC (CD11c(+) major histocompatibility complex class II-positive [MHC- II+] cells) were present following bacterial administration, and confocal m icroscopy showed that GFP-expressing bacteria were contained within CD11c() MHC-II+ splenocytes. Furthermore, splenic DC and T cells were activated f ollowing Salmonella infection. This was shown by increased surface expressi on of CD86 and CD40 on CD11c(+) MHC-II+ cells and increased CD44 and CD69 e xpression on CD4(+) and CD8(+) T cells. Salmonella-specific gamma interfero n (IFN-gamma)-producing cells in both of these T-cell subsets, as well as c ytolytic effector cells, were also generated in mice given live bacteria. T he frequency of Salmonella-specific CD4(+) T cells producing IFN-gamma was greater than that of specific CD8(+) T cells producing IFN-gamma in the sam e infected animal. This supports the argument that the predominant source o f IFN-gamma production by cells of the specific immune response is CD4(+) T cells. Finally, DC that phagocytosed live or heat-killed Salmonella in vit ro primed bacterium-specific IFN-gamma -producing CD4(+) and CD8(+) T cells as well as cytolytic effector cells following administration into naive mi ce. Together these data suggest that DC are involved in priming naive T cel ls to Salmonella in vivo.