Better responses of virus-specific CD8⁺ T cells and their prolonged survival in <i>Oasl1</i> KO mice due to virus-specific T-cell-extrinsic factors.

<p>GP33-specific TCR transgenic CD8⁺ T cells, P14 cells, were obtained from naïve P14 Thy1.1 congenic mice. 5×10³ of P14 Thy1.1⁺ CD8⁺ T cells were adoptively transferred into WT and <i>Oasl1</i> KO mice. The next day, both recipient mice were infected with LCMV CL-13 and splenocytes were isolated from the mice at 5 d p.i. (<b>A</b>) Massive expansion of virus-specific donor CD8⁺ T cells in the KO mice. Numbers in the representative plot (left) indicate the frequency of donor P14 Thy1.1⁺ CD8⁺ T cells among splenocytes while the absolute numbers of donor P14 Thy1.1⁺ CD8⁺ T cells present per recipient spleen are summarized in the graph (right). (<b>B</b>) Cytokine production from donor P14 Thy1.1⁺ CD8⁺ T cells after <i>in vitro</i> restimulation with GP33 peptide. Representative plots (left) are shown for co-expression of IFN-γ and TNF-α or IFN-γ and IL-2 on donor P14 Thy1.1⁺ CD8⁺ T cells; summarized graph (right) for the frequency of TNF-α- or IL-2-producing cells among IFN-γ⁺ CD8⁺ T cells. (<b>C</b>) Proliferative capability measurement on donor P14 Thy1.1⁺ CD8⁺ T cells by direct <i>ex vivo</i> staining. Representative Ki67 expression levels (MFIs, left) and summarized levels (right) on donor P14 Thy1.1⁺ CD8⁺ T cells are shown. Shade histogram indicates Ki67 expression level on P14 Thy1.1⁺ CD8⁺ T cells before adoptive transfer (a.t.); black line and red line histograms indicate Ki67 expression levels on P14 Thy1.1⁺ CD8⁺ T cells at 5 d p.i. after a.t. into WT and KO mice, respectively. (<b>D</b>) Cell death susceptibility of donor P14 Thy1.1⁺ CD8⁺ T cells. Representative (left) and summary (right) data after direct <i>ex vivo</i> staining of splenocytes for Annexin V (AV) and 7AAD. Donor P14 Thy1.1⁺ CD8⁺ T cells were analyzed. Data are given as mean + SD. Data are representative of two independent experiments (<i>n</i> = 4 per group in each experiment). ns, not significant; **, <i>P</i><0.01; ***, <i>P</i><0.001.