IFN-γ Control of an Effector/Target Combination for Skin Allograft Rejection: Macrophage/Skin Components in Normal Mice or T Cell/Endothelial Cells in IFN-γ-Deficient Mice.

Organ, skin, or cell allografts are acutely rejected from normal mice, whereas vascularized organ allografts, but not allografted Meth A cells, are rejected from interferon-γ (IFN-γ)-deficient mice. Here we explored effector/target combinations for i.p. allografted Meth A (cytotoxic T lymphocyte [CTL]-resistant) or RLmale1 (CTL-susceptible) cells into or for BALB/c skin (skin components: CTL resistant) onto normal or IFN-γ-deficient C57BL/6 mice. After allografting, normal mice showed more infiltration but only a little thrombosis/hemorrhage. Monocyte/macrophage MHC receptor (MMR)+ macrophages (on days 5-10) and T cell receptor (TCR)+ CTLs (on days 7-9) were cytotoxic against Meth A cells or skin components and RLmale1 cells, respectively, and the allografts were rejected. After allografting into IFN-γ-deficient mice, MMR- macrophages and highly activated TCR+ CTLs were induced, and the mice died of hemorrhagic ascites with Meth A cells and more acutely rejected RLmale1 cells. The CTLs on days 4-6 were inactive toward skin components at an in vivo effector/target ratio but injured endothelial cells to cause severe thrombosis/hemorrhage and more acute rejection of skin allografts. These results indicate that IFN-γ-dependent MMR expression was essential for macrophage-mediated cytolysis of allogeneic skin components and that IFN-γ-deficient mice more acutely rejected skin allograft by causing CTL-induced injury to endothelial cells.