Histologic examination of GvHD.

Induction of lethal acute GvH reactions after adoptive transfer of allogeneic donor T lymphocytes or donor T cells depleted of alloreactivity by AICD was examined histologically and by immunohistology as described in “Materials and methods.” On day 6 after transfer, 2 mice from each group were killed and tissue from skin, liver, spleen, small intestine, and lymph nodes was fixed or embedded. Depicted are sections of skin (A) and small intestine (B) (magnifications of 100 μm and 200 μm) stained by hematoxylin and eosin, which show cells in the basal layer of the epidermis undergoing apoptosis and lymphocytic infiltrations into the cryptic epithelium of small intestine following adoptive transfer of allogeneic donor cells. In addition, immunohistology (shown in red) revealed massive expansion of CD4⁺ T cells and, albeit to a lesser extent, of CD8⁺ T cells in spleen (C) isolated from F₁recipients that had received untreated allogeneic donor T cells. In contrast, no significant GvHD histopathology could be detected in recipients administered donor T lymphocytes subjected to AICD prior to transfer.