Indirect allorecognition: not simple but effective.

Donor dendritic cells are potent but short-lived stimulators of early transplant rejection, and recipient antigen presenting cells presenting donor major histocompatibility complex peptides sustain immunoreactivity and contribute to chronic rejection. We briefly consider how CD4 T cells that recognize allopeptide can provide help for effector and regulatory responses and highlight the implications for promoting graft survival.