Figure 5: T cell surveillance model of mixed chimerism. (A) In the BXSB lupusprone mouse, mature T cells positively selected in the host thymus can interact with B cells. However, BXSB mice are unable to selectively suppress auto-reactive Ab production through TCR/MHC interaction. (B) In the fully MHC-matched chimeric BXSB mouse, T cells derived from donor bone marrow can suppress both host and donor auto-reactive B cells through TCR/ MHC interaction. (C) In the fully MHC-mismatched chimeric BXSB mouse, all peripheral T cells can recognize host-type MHC because they were positively selected by host thymic epithelial cells. Therefore, T cells cannot interact with donor B cells expressing donor-type MHC or suppress auto-reactive Ab producing donor B cells.