Plasmacytoid dendritic cells mature independently of MyD88 and IFN-αβR in response to Listeria and stimulate CD8 T cells.

Plasmacytoid dendritic cells (pDCs) are a subpopulation of dendritic cells specialized in the production of IFN-α/β, particularly during viral infections. In this way pDCs directly impact antiviral immunity and influence T cell activation. However, despite their role as modulators of the immune response, their function as antigen-presenting cells (APCs) remains poorly understood. Indeed, their capacity as APCs during bacterial infections is unexplored. Here we investigate the importance of MyD88 and IFN-α/β in upregulating costimulatory molecules on pDCs during Listeria infection and their impact on activation of naïve CD8 T cells. We show that pDCs efficiently upregulate CD80 and CD86 during systemic Listeria infection, yet express lower levels of these molecules than conventional dendritic cells (cDCs). Furthermore, pDCs are able to stimulate CD8 T cell proliferation and IFN-γ production, although less efficiently than cDCs. Despite these differences, the influence of MyD88 and IFN-α/β on CD80 and CD86 expression on pDCs and cDCs is similar. Thus, our data show for the first time the potential of pDCs to activate CD8 T cells in response to a bacterial infection.