Consistent with previous reports in other models that PD-L1 is also expressed on T cells and is further upregulated during activation [4], PD-L1 was upregulated on virtually all CD4+ and CD8+ T cells by day 5 of PbA infection in both C57BL/6 and BALB/c mice (Figure S1A in Text S1). This evidence concerns the gene CD8A and infection.