T-cell loss during murine acquired immunodeficiency syndrome was mediated through programmed death-1. Wild-type (Wt) and programmed death-1 (PD-1) knockout (KO) mice infected with LP-BM5 were assessed for lymphopenia by examining peripheral blood mononuclear cell (PBMC) preparations at 8 w post-infection (p.i.). PBMC were stained with CD4-eFlour450, CD8-PE-Cy7 and CD3-APC-Cy7 mAbs and analyzed by flow cytometry. (A) Representative flow cytometry contour plots depicting the ratio of CD4+ and CD8+ T-cells from Wt and PD-1 KO animals infected with LP-BM5 are shown. (B) The percentages of CD4+ and CD8+ T-cells in the PBMC preparations were determined at 8 w p.i. Data show the mean (± standard error) percentage of T-cells pooled from three independent experiments. *
P <0.01 versus Wt.