Antibody-mediated rejection of donor BM in primed mice is far more rapid than T-cell–mediated rejection in naive mice. Shown are images of BALB/c mice irradiated with 3.5 Gy on day −1 and infused with 20 × 106 B6 GFP+ T-cell–depleted BM cells on day 0. (A-G) Left panels (rejection) indicate untreated mice that ultimately reject their grafts in a T-cell–dependent fashion. Middle panels (engraftment) indicate mice that received anti-CD4 and anti-CD8 mAbs in vivo around the time of transplantation to ensure long-term donor engraftment. Right panels (primed rejection) indicate mice primed with B6 splenocytes on day −28 that reject their donor BM grafts via preformed alloantibody. (H-I) Nonprimed and primed mice as indicated were imaged 3 hours after BMT. Representative images from 1 of 3 mice are shown. See “Materials and methods” for imaging details.