Early expansion of CD4⁺ donor T cells depends on FasL function.

Highly enriched CD4⁺ T cells were obtained from spleens of B6, B6-pko, B6-gld, and B6-cdd mice by means of magnetic beads on Macs column (see “Materials and methods”). Then, 1 × 10⁶donor CD4⁺ T cells were combined with 5 × 10⁶ T-cell–depleted B6-Ly5.1 bone marrow cells and injected into BALB/c recipients (2 per group) irradiated at 5.5-Gy (A) or 11-Gy (B) TBI 24 hours earlier. At day 5, the mesenteric lymph nodes were harvested from individual recipient mice and counted. Donor T cells were identified by staining with anti-CD4, anti–H-2K^b, and anti-Ly5.1 mAbs. The percentage of CD4⁺H-2K^b+Ly5.1⁻ cells × the total number of nucleated lymph node cells was used to determine donor cell numbers. (A) B6-cdd and B6-gld versus B6: P < .0014. B6-pko versus B6: P > .5. (B) B6-cdd, B6-gld, and B6-pko versus B6-wt: P > .5.