CD8A and infection: In contrast, the infection of B cells and Gr-1+ cells was associated with a significant increase in PD-L1 expression in comparison to naive cells (day 0) or to non-infected (gp70-) cells harvested at the same time point after infection (Fig 2B and 2C) This increase had two phases, it started early at 4 dpi but was most pronounced at 7–12 dpi corresponding with the expansion of cytotoxic CD8+ T cells at this later time point [26].