Donor T cells from IFNγR^−/− recipients are hyperresponsive to alloantigens. Splenocytes from G-CSF–mobilized Balb/c donors were transplanted into irradiated (1000 rad) wt or IFNγR^−/− B6 recipients. Analyses were performed 9 days after transplantation. (A) Absolute numbers of donor splenic T cells, CD11b⁺ monocytes/neutrophils, and B cells (n = 4-5 in allogeneic T-cell-replete and n = 3 in TCD groups). (B) IFNγ, IL-5, and TNFα determined in sera by cytokine bead array. **P < .01 (n = 10-17). (C) Purified donor (H-2D^d+) CD4⁺ T cells were sort-purified (> 95%) from wt or IFNγR^−/− recipients and restimulated with purified DCs. IL-5 and IL-4 were measured in supernatants by cytokine bead arrays, while IFNγ was measured by ELISA. Data are means plus or minus SE of triplicate wells and is 1 of 3 representative experiments is shown. ND indicates not detected. (D) Purified donor CD8⁺ (H-2D^d+) T cells were sort-purified (> 95%) from wt or IFNγR^−/− recipients and used as effectors in ⁵¹Cr-release CTL assays against host-type EL4 targets and donor-type A20 targets. Data represent means plus or minus SE of triplicate wells combined from 2 replicate experiments. ***P < .001, wt antihost versus IFNγR^−/− antihost.