A subset of human plasmacytoid dendritic cells expresses CD8α upon exposure to herpes simplex virus type 1

Classical and plasmacytoid dendritic cells (DC) play important roles in the defense against murine and human infections with herpes simplex virus (HSV). So far, CD8 alpha expression has only been reported for murine DC. CD8 alpha(+) DC have prominent cross-presenting activities, which are enhanced by murine CD8 alpha(+) PDC. The human orthologue of murine CD8 alpha(+) DC, the CD141 (BDCA3)(+) DC, mainly cross-present after TLR3 ligation. We report here the serendipitous finding that a subset of human PDC upregulates CD8 alpha upon HSV-1 stimulation, as shown by gene array and flow cytometry analyses. CD80i, not CD8 beta, was expressed upon exposure. Markers of activation, migration, and costimulation were upregulated on CD8 alpha-expressing human PDC. In these cells, increased cytokine and chemokine levels were detected that enhance development and function of T, B, and NK cells, and recruit immature DC, monocytes, and Th1 cells, respectively. Altogether, human CD8 alpha(+) PDC exhibit a highly activated phenotype and appear to recruit other immune cells to the site of inflammation. Further studies will show whether CD8 alpha-expressing PDC contribute to antigen cross-presentation, which may be important for immune defenses against HSV infections in vitro and in vivo.