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. Author manuscript; available in PMC: 2010 May 1.
Published in final edited form as: Immunol Rev. 2009 May;229(1):294–306. doi: 10.1111/j.1600-065X.2009.00776.x

Figure 2.

Figure 2

Heterologous immunity to pathogens is a potent barrier to transplantation tolerance/long-term graft survival induced by costimulation blockade. A, Naïve donor-reactive T cells encounter donor antigen under the cover of costimulation blockade, fail to fully differentiate, undergo apoptosis, and therefore fail to mediate destruction of the graft. B, Memory T cells specific for pathogen-derived epitopes presented by self MHC may cross-react with donor-derived MHC and become activated. By virtue of their reduced requirement for CD28 and CD40 mediated costimulation during reactivation, these pathogen-derived memory T cells may then expand, differentiate, and mediate graft destruction.