Magnitude of memory to the major histocompatibility complex

ALTHOUGH the phenomenon of memory is central to the adoptive immune response to antigenic stimulation, the magnitude of the memory effect in graft rejection has never been quantified. We have directly compared the potency of naive and memory cells in two quantitative adoptive transfer assays, one measuring graft rejection and the other graft-versus-host activity. While the well known lack of a significant factor of immunisation in the latter was confirmed, memory cells showed a dramatic, long term increase in their potency to reject heart grafts.