Background. We evaluated the importance and mechanism of graft and host accommodation in hamster-to-rat cardiac xenotransplantation models.
Methods. To evaluate graft accommodation, accommodated hamster grafts (Group 2) were transplanted to naive host rats treated with FK506, and compared with naive hamster grafts (Group 1). To evaluate host accommodation, three groups were evaluated: naive hamster hearts were transplanted to naive hosts treated with FK506 (Group 3: 0.5 mg/kg, Group 4: 1.0 mg/kg) and splenectomy, and compared with accommodating hosts (Group 5) with FK506 0.5 mg/kg and splenectomy. We examined graft survival, histopathology, antihamster antibodies and B-1 cells in blood.
Results. Graft survival in Group 2 (3.4 +/- 0.9 days) was not significantly different from that in Group 1 (2.8 +/- 0.4 days). Graft survival in Groups 4 and 5 (> 30 days) was significantly prolonged compared with that in Group 3 (6.0 +/- 0.7 days). Histopathology of Groups 1-3 showed humoral rejection, whereas Groups 4 and 5 showed normal histology and expression of protective genes. In Groups 1-3, antihamster immunoglobulin (Ig) M and B-1 cells increased significantly compared to Groups 4 and 5, where IgM and B-1 cells remained low or were reduced.
Conclusions. Host accommodation was more important than graft accommodation. Accommodating grafts expressing protective genes were rejected with an elevation of both IgM and B-1 cells. In accommodated hosts, both IgM and B-1 cells decreased, suggesting that B-1 cells may be responsible for the production of antihamster antibodies. These results suggest that sufficient suppression of B-1 cells, resulting in decreased titers of antihamster antibodies, may play an important role in host accommodation.