Spleen cells were isolated from naive B6 mice and cultivated with F-MuLV infected Mus Dunni cells to infect mouse cells in vitro. Multi-parameter flow cytometry was used to determine PD-L1 expression (MFI) (A) and the percentage of PD-L1^high cells (B) in different target cell populations of FV. C. Ter119⁺, CD19⁺, and Gr-1⁺ cells were isolated from naïve wild type mice and were infected with F-MuLV in vitro. mRNA from infected and non-infected cells was isolated for real time PCR quantification of the IFNα mRNA expression. The numbers of IFNα mRNA copies in relation to 10⁵ copies of mRNA for β-actin is shown. Data was pooled from at least two independent experiments with similar results. Spleen cells were isolated from naїve wild type mice or from naïve IFNAR1^-/- mice and cultivated with F-MuLV infected Mus Dunni cells to infect mouse cells in vitro. Multi-parameter flow cytometry was used to determine PD-L1 expression (MFI) on infected CD19⁺ and Gr-1⁺ cells (D) and in the presence of IFNα (E) Data was pooled from at least two independent experiments with similar results. F. Multi-parameter flow cytometry was used to determine the expression of PD-L1 on the sur-face of gp70⁺Ter119⁺, gp70⁺CD19⁺, and gp70⁺Gr-1⁺ cells isolated from spleens of 6 day FV infected WT and IFNAR1^-/- mice. Data was pooled from two independent experiments with similar results. Multi-parameter flow cytometry was used to determine the expression of PD-L1 on the surface of human CD4⁺ T cells after HIV-1 infection. Representative histograms of PD-L1 expression on human CD4⁺ T cells non-stimulated and non-infected, stimulated in vitro with PHA and infected with HIV-1 or cells only stimulated with PHA are shown. The data is shown for day three, seven and ten after infection (G). Expression of PD-L1 on human CD4⁺ T cells (H) and the percentage of PD-L1^high CD4⁺ T cells (I) in populations of non-stimulated and non-infected, stimulated in vitro with PHA and infected with HIV-1 or cells only stimulated with PHA are shown at day ten after infection. Mean numbers plus SD from three independent experiments with similar results was shown. Differences between FV infected (gp70⁺) and FV non-infected (gp70^-) mice cells were analyzed by an unpaired t-test. Differences between HIV infected (p24⁺) and HIV non-infected (p24^-) CD4⁺ cells were analyzed by Mann-Whitney t test. Statistically significant differences between the groups are indicated in the figure (*p˂0.05, **p˂0.005).

https://doi.org/10.1371/journal.ppat.1005364.g001