In vitro parameters of donor-antigen-specific tolerance.

Donor-antigen-specific tolerance to the allograft is increasingly considered a reachable goal in the field of transplantation. As our understanding of the processes that govern donor-specific tolerance increases, so must our understanding of ways to detect this state of affairs. Unfortunately, this is not a straightforward procedure, as the mechanisms which govern tolerance are multiple and varied. Previously, the mixed lymphocyte reaction was used as standard to detect unresponsiveness. This approach is not valid for detecting tolerance because it only measures both direct pathway, naïve and memory responses, whereas the indirect pathway and 'pure' memory responses are more informative parameters for detecting tolerance. Techniques, such as the trans vivo delayed-type hypersensitivity assay, ELISPOT and antigen-specific HLA tetramer analysis address this problem, and the numbers of cell subsets, such as dendritic cells and NKT cells, can also aid us in detecting donor-antigen-specific tolerance.