Donor APCs are required for the propagation of GVHD. Lethally irradiated (900 cGy) Balb Rag mice received transplants of B6 Rag BM to create chimeric animals in which APCs were of donor origin. In reciprocal studies, lethally irradiated (1000 cGy) B6 Rag animals received transplants of Balb Rag BM. Chimeric mice were bled 60 days after transplantation, and peripheral blood cells were determined to be more than 95% donor origin. Spleen cells (containing 0.6 × 106 T cells) from B6→Balb mice undergoing GVHD were then adoptively transferred into either B6 Rag BM→Balb Rag (▪, n = 10) or Balb Rag BM→B6 Rag (□, n = 8) chimeras 2 months after their initial transplantation. B6 Rag animals (n = 19) that received spleen cells containing 1 × 106 T cells from normal B6 mice served as pathologic controls. Weight loss (A), incidence (B), and severity of colitis (C) are depicted. Results are cumulative data from 2 experiments. Error bars depict SEM.
