Alloantigen presentation and GVHD in the absence of radiosensitive host hematopoietic-derived APCs. (A) Experimental schema: β2m^−/−♂→B6♂ chimeras were generated as described in “Methods.” They were then irradiated with 9 Gy and transplanted with TCD BM from β2m^−/− animals along with T cells from B6♂ or BALB/c♀ donors and analyzed for donor T-cell expansion. (B) Total donor CD45.1⁺CD8⁺ or H2kd⁺CD8⁺ T cells expansion. (C) Donor CD8⁺IFN-γ⁺ T cell number and (D) serum levels of IFN-γ. Data from 1 of 2 similar experiments are shown. (E) GVH responses induced by host nonhematopoietic APCs depend on T-cell precursor frequency. Survival and GVHD score. Data from 1 of 2 similar experiments are shown. (F-H) Male nonhematopoietic cells can stimulate both H-Y Ag-specific T cells and allogenic T cells. (F-G) Marilyn CD4 T cells against male liver endothelial cells (H) and epithelial cells of small intestine (G). (H) B6 male–derived liver endothelial cells can stimulate allogeneic BALB/c T cells. (I-J) Class II expression on liver endothelial cells gated by CD146⁺ cells, (right) naive and (left) IFN-γ stimulation for 48 hours (I). (J) Bar graph of class II expression on liver endothelial cells. Data are from 1 of 3 similar experiments.