Figure 1: Roles of LEC in CD4 and CD8 T-cell tolerance. LEC transcriptionally express a variety of PTA, which are directly presented to CD8 T-cells, leading to CD8 T-cell proliferation and death through the combined effects of PD-1/PD-L1 signaling and a lack of costimulation. LEC do not directly present PTA on MHC II, but instead transfer the PTA to DC, which induce CD4 T-cell anergy. LEC can acquire peptide/MHC II complexes generated by DC, which are then presented by the LEC, leading to CD4 T-cell apoptosis. Finally, LEC can cross-present soluble antigens from the lymph, leading to dysfunctional CD8 activation and increased apoptosis. It is unknown whether soluble antigens can be presented by LEC on MHC II to CD4 T-cells.