Cross-primed CD8(+) T cells mediate graft rejection via a distinct effector pathway

To prevent bystander destruction of healthy host tissues, cytotoxic CD8(+) T lymphocytes are fitted with specific receptors that direct their destructive forces specifically against chosen targets. We show here, however, that anti-H-Y monospecific, H-2(b-restricted MataHari CD8(+) T cells reject H-2(k) male skin grafts, with which they cannot directly interact. Such rejection is interferon-gamma-dependent and only occurs if the recipient endothelium expresses H-2(b). The findings suggest an alternate indirect effector pathway that requires processing and presentation of the donor H-Y antigen by recipient endothelium and have implications for both transplantation and autoimmune disease.