Skin Graft Rejection Elicited by β2-Microglobulin as a Minor Transplantation Antigen Involves Multiple Effector Pathways: Role of Fas-Fas Ligand Interactions and Th2-Dependent Graft Eosinophil Infiltrates

Abstract

β2-Microglobulin (β2m)-derived peptides are minor transplantation Ags in mice as β2m-positive skin grafts (β2m+/+) are rejected by genetically β2m-deficient recipient mice (β2m−/−). We studied the effector pathways responsible for the rejection induced by β2-microglobulin-derived minor transplantation Ags. The rejection of β2m+/+ skin grafts by naive β2m−/− mice was dependent on both CD4 and CD8 T cells as shown by administration of depleting mAbs. Experiments performed with β2m−/−CD8−/− double knockout mice grafted with a β2m+/+ MHC class I-deficient skin showed that sensitized CD4 T cells directed at β2m peptides-MHC class II complexes are sufficient to trigger rapid rejection. Rejection of β2m+/+ grafts was associated with the production of IL-5 in vitro, the expression of IL-4 and IL-5 mRNAs in the grafted tissue, and the presence within rejected grafts of a considerable eosinophil infiltrate. Blocking IL-4 and IL-5 in vivo and depleting eosinophils with an anti-CCR3 mAb prevented graft eosinophil infiltration and prolonged β2m+/+ skin graft survival. Lymphocytes from rejecting β2m−/− mice also displayed an increased production of IFN-γ after culture with β2m+/+ minor alloantigens. In vivo neutralization of IFN-γ inhibited skin graft rejection. Finally, β2m+/+ skin grafts harvested from B6lpr/lpr donor mice, which lack a functional Fas molecule, survived longer than wild-type β2m+/+ skin grafts, showing that Fas-Fas ligand interactions are involved in the rejection process. We conclude that IL-4- and IL-5-dependent eosinophilic rejection, IFN-γ-dependent mechanisms, and Fas-Fas ligand interactions are effector pathways in the acute rejection of minor transplantation Ags.