T-cell expansion after the infusion of B6 and T-bet^−/− LN cells. CByB6F1 mice that received TBI only (n = 11), B6 LN (n = 13), or T-bet^−/− LN (n = 16) treatment were analyzed for CD4 and CD8 T-cell expansion in the BM shown as representative histograms (A) and means with SEs (B). There was drastic expansion (P < .01) of infused B6 T cells but not infused T-bet^−/− T cells. We also analyzed the proportion of BM CD4 and CD8 T cells that express IFN-γ, shown as representatives (C) and means with SEs (D), because there was also significant expansion of IFN-γ–expressing CD4 (P < .05) and IFN-γ–expressing CD8 (P < .01) T cells in mice that received infusion of B6 LN cells but not T-bet^−/− LN cells.