The mechanism of prolonged graft survival following removal of the regional lymph node.

The immune responsiveness of rats in which the rejection of RT-1-incompatible neonatal heart grafts had been prevented by removal of the draining lymph node was examined. It was found that within three days of node removal animals developed a state of specific unresponsiveness characterized by the failure to reject secondary grafts made into the contralateral leg with intact draining nodes. Studies of recipients with long-surviving grafts revealed that their serum contained significant levels of cytotoxic alloantibody although their cells behaved like those from naive donors in mixed lymphocyte interactions, graft-versus-host responses, and adoptive allograft assays. There was no evidence for the presence of sensitized T cells or suppressor T cells in the tissues of recipients with long-surviving grafts. The findings support the suggestion that prolonged graft survival following node removal is due to enhancement actively induced by the passage of graft antigen into the circulation at a time when the induction of the cell-mediated response has been aborted by removal of the node regional to the graft.