Microchimeric cells from the peripheral blood associated with cardiac grafts are bone marrow derived, long-lived and maintain acquired tolerance to minor histocompatibility antigen H-Y

Background. Although it has been well established that the microchimerism o ccurs in the peripheral blood of the recipients after various settings in b oth clinical and experimental organ transplantation, nevertheless, their ro les in inducing and maintaining acquired transplantation tolerance are cont roversial. Furthermore, regarding the cell lineages, kinetics, and function s of the cells that constitute the microchimerism after organ transplantati on, solid information is not available. Methods. Using rat heterotopic heart isografts from bone marrow chimeras be tween cross-sex and applying polymerase chain reaction with specific primer s to rat sex determining region of Y chromosome, a relationship between a s tate of microchimerism and induction as well as maintenance of acquired tol erance to H-Y antigen were examined. Results. Microchimeric cells of the peripheral blood (MCPB) after cardiac g rafting contain bone marrow-derived and radiation-sensitive cells. Furtherm ore, removal of the primary cardiac grafts revealed that microchimeric cell s in the peripheral blood are long-lived cells, i.e., more than 6 months. W hen the female rats that had contained long-lasting MCPB, were innoculated with syngeneic male dendritic cells, failure to sensitize female toward mal e specific antigen H-Y was found to occur. Conclusions. Thus it was suggested that radiation-sensitive, bone marrow de rived, long-lived MCPB play a significant role in maintaining acquired tran splantation tolerance to minor histocompatibility antigen H-Y.