Alloreactive cytotoxic CD4(+) responses elicited by cytomegalovirus-infected endothelial cells: Role of MHC class I antigens

Cytomegalovirus (CMV) has been associated with chronic graft rejection in s olid organ transplant patients. To elucidate the mechanism by which CMV lea ds to graft rejection, we hypothesized that CMV infection of endothelial ce lls could stimulate alloreactive cytotoxic T lymphocytes (CTL). This hypoth esis was explored using the following experimental model: peripheral blood mononuclear cells (MNC) obtained from normal hosts were grown on monolayers of umbilical vein endothelial cells (UVEC) infected with CMV (CMV-UVEC) or not (control) and tested for CTL activity against uninfected UVEC, We show ed that CMV-UVEC-stimulated MNC have significant CTL activity against uninf ected UVEC, The CTL activity elicited by CMV-UVEC stimulation was significa ntly higher compared with that stimulated by uninfected UVEC or by ganciclo vir-treated CMV-UVEC, indicating the critical role of productive CMV infect ion. The CTL activity was specific for the UVEC used as stimulators and did not affect MHC-unrelated UVEC, However, lymphoblastoid lines (LBL) major h istocompatibility complex (MHC)-identical with the stimulator UVEC were als o killed by the CMV-UVEC-stimulated MNC, CTL killed identical UVEC and LBL in a competitive fashion. Blocking experiments with monoclonal antibodies ( mAbs) identified CD4 cells as the main effector of CTL activity and MHC cla ss I as the antigenic target of CTL, Although natural killer (NK) cells did not significantly contribute to the CTL activity of CMV-UVEC-stimulated MN C, their presence in the MNC cultures during the stimulation process was cr itical for the development of CTL, This model offers a framework for unders tanding the role of CMV infection in graft rejection and for devising preve ntative strategies.