Type I IFN signaling drives BM accumulation of activated, antigen-specific CD8 T cells. (A and B) Total cell counts of BM CD8 T lymphocytes (A) and gp33⁺ LCMV-specific BM CD8 T cells (B). Black bars, control mice treated with PBS before or after infection; red bars, data from mice treated with a-IFNAR blocking antibody during infection (see Materials and methods for dosage and regimens). (C) Contour plot of intracellular immunostaining for IFNγ and TNFα in BM CD8 T cells 14 dpi with or without a-IFNAR treatment. (D) Histograms showing PD-1 (left) and Tim-3 (right) expression of BM CD8 T cells 14 dpi in control and a-IFNAR–treated mice. (E) Total number of IFNγ⁺ CD8 T cells. (F) IFNγ⁺TNF-α⁺ CD8 T cells. (G) Percentage of PD-1^hiTim-3⁺ T cells in total BM CD8 T cells at 14 dpi. (H) Total BM cellularity. (I and J) BM erythroid progenitors (I) and Lin⁻c-kit⁺ progenitor cells (J; n = 5–7 mice from two or three independent experiments). Statistics were analyzed using two-tailed Mann–Whitney U test with *, P < 0.05; **, P < 0.01; ***, P < 0.001; ns, P > 0.05.