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.

Eosinophils: Singularly destructive effector cells or purveyors of immunoregulation?

“…18 For example, IL-4-deficient mice have reduced transplant-associated eosinophilia and impaired T H 2 inflammation at the site of incompatible allograft transplants, suggesting that eosinophils may modulate the immune responses leading to transplant rejection. 19 In addition, both IL-4 and IL-13 are associated with tumor cell death in many types of cancer, 20 and our recent studies using eosinophil-specific antibodies have demonstrated that nearly all human and/or mouse cancers are associated with a robust eosinophil infiltrate at some point in tumor growth. 21 Thus, although further analyses are certainly needed, it is interesting to speculate that eosinophils may be a little recognized participant in the modulation of tumor-associated T H 2 immune responses (or alternatively the downregulation of tumor-associated cytotoxic T H 1 responses).…”

IL-4 Deficiency Prevents Eosinophilic Rejection and Uncovers a Role for Neutrophils in the Rejection of MHC Class II Disparate Skin Grafts

“…Skin grafts were prepared from tails of female mice and grafted onto the flanks of the recipients as previously described (1,10). Vaseline gauze was placed over the graft and sticking plaster was applied around the trunk.…”

Effects of T Cell Frequency and Graft Size on Transplant Outcome in Mice

“…Untreated recipients rapidly reject fully allogeneic heart and skin grafts (10,11,22). In contrast, minor Ag-disparate transplants prime lower frequencies of effector T cells, often with the same proinflammatory phenotype as T cells induced to a fully allogeneic graft (7,10,17,22,25,26). Nonetheless, such minor Ag-disparate grafts are rejected at a slower pace than MHC-disparate grafts, and in some situations minor Ag-disparate transplants are not rejected at all (7,10,17).…”