IFN-γ signaling is necessary for MHC up-regulation. Immunostaining for MHC I (H2-D^b), MHC II (I-A^b) in the liver (A; magnification 100×) and intestine (B; magnification 100× for H2-D^b and 200× for I-A^b) of syngeneic (wt) and allogeneic (wt and IFN-γRKO) recipients on day 8 after transplantation. Positive staining is red for hepatic and brown for intestinal tissues. Biliary ducts (bd) and intestinal submucosa (sm) are indicated by arrows. Staining with isotype controls was negative and omitted from the figure for clarity. One representative experiment of 3 is shown. (C) One representative set of data out of a minimum of 3 showing CD107a expression on donor CD8 T lymphocytes from the spleen, liver, and intestine. No CD8-positive population could be detected in syngeneic hosts' intestines on day 8 after transplantation. (D) Proportion of CD107a⁺ cells among CD8⁺ T cells in the spleen of syngeneic and allogeneic recipients. Histograms represent the mean and SD for at least 3 mice per group, from 3 independent experiments. **P < .01.