In Vivo Activation of Dendritic Cells and T Cells duringSalmonella entericaSerovar Typhimurium Infection

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Abstract
The present study was initiated to gain insight into the interaction between splenic dendritic cells (DC) andSalmonella entericaserovar Typhimurium in vivo. Splenic phagocytic cell populations associated with green fluorescent protein (GFP)-expressing bacteria and the bacterium-specific T-cell response were evaluated in mice givenS. entericaserovar Typhimurium expressing GFP and ovalbumin. Flow cytometry analysis revealed that GFP-positive splenic DC (CD11c+major histocompatibility complex class II-positive [MHC-II+] cells) were present following bacterial administration, and confocal microscopy showed that GFP-expressing bacteria were contained within CD11c+MHC-II+splenocytes. Furthermore, splenic DC and T cells were activated followingSalmonellainfection. This was shown by increased surface expression of CD86 and CD40 on CD11c+MHC-II+cells and increased CD44 and CD69 expression on CD4+and CD8+T cells.Salmonella-specific gamma interferon (IFN-γ)-producing cells in both of these T-cell subsets, as well as cytolytic effector cells, were also generated in mice given live bacteria. The frequency ofSalmonella-specific CD4+T cells producing IFN-γ was greater than that of specific CD8+T cells producing IFN-γ in the same infected animal. This supports the argument that the predominant source of IFN-γ production by cells of the specific immune response is CD4+T cells. Finally, DC that phagocytosed live or heat-killedSalmonellain vitro primed bacterium-specific IFN-γ-producing CD4+and CD8+T cells as well as cytolytic effector cells following administration into naı̈ve mice. Together these data suggest that DC are involved in priming naı̈ve T cells toSalmonellain vivo.