Immune Evasion by Yersinia enterocolitica: Differential Targeting of Dendritic Cell Subpopulations In Vivo

CD4⁺ T cells are essential for the control of Yersinia enterocolitica (Ye) infection in mice. Ye can inhibit dendritic cell (DC) antigen uptake and degradation, maturation and subsequently T-cell activation in vitro. Here we investigated the effects of Ye infection on splenic DCs and T-cell proliferation in an experimental mouse infection model. We found that OVA-specific CD4⁺ T cells had a reduced potential to proliferate when stimulated with OVA after infection with Ye compared to control mice. Additionally, proliferation of OVA-specific CD4⁺ T cells was markedly reduced when cultured with splenic CD8α⁺ DCs from Ye infected mice in the presence of OVA. In contrast, T-cell proliferation was not impaired in cultures with CD4⁺ or CD4⁻CD8α⁻ DCs isolated from Ye infected mice. However, OVA uptake and degradation as well as cytokine production were impaired in CD8α⁺ DCs, but not in CD4⁺ and CD4⁻CD8α⁻ DCs after Ye infection. Pathogenicity factors (Yops) from Ye were most frequently injected into CD8α⁺ DCs, resulting in less MHC class II and CD86 expression than on non-injected CD8α⁺ DCs. Three days post infection with Ye the number of splenic CD8α⁺ and CD4⁺ DCs was reduced by 50% and 90%, respectively. The decreased number of DC subsets, which was dependent on TLR4 and TRIF signaling, was the result of a faster proliferation and suppressed de novo DC generation. Together, we show that Ye infection negatively regulates the stimulatory capacity of some but not all splenic DC subpopulations in vivo. This leads to differential antigen uptake and degradation, cytokine production, cell loss, and cell death rates in various DC subpopulations. The data suggest that these effects might be caused directly by injection of Yops into DCs and indirectly by affecting the homeostasis of CD4⁺ and CD8α⁺ DCs. These events may contribute to reduced T-cell proliferation and immune evasion of Ye.