Analysis of PCR microchimerism induced by intrathymic inoculation of donor alloantigens in rats.

Intrathymic injection of donor alloantigens (splenocytes) was performed in rat heart transplantation to induced tolerance. In our experimental protocol, male (BN rats, RT1n) heart allografts were transplanted to female (LEW rats, RT1(1)) recipients in order to detect the existence of Y-chromosomes in recipients' tissues using the polymerase chain reaction (PCR) after the establishment of microchimerism. The mean survival time (MST) of male heart allografts was prolonged by the thymic injection protocol. PCR analysis of the Y-chromosomes of these recipients showed that splenocytes inoculated into the thymus still remained after as long as 30 days, while none of the cells that originated from the donor were never detected in the peripheral blood. On the other hand, our previous study demonstrated that the donor-specific Y-chromosomes could be detected in all the tissues of the females (peripheral blood, lymph nodes, spleen, and liver) except for thymus, of the sex-mismatched rat liver transplantation without thymic injection. Completely inconsistent results were deduced from two of our experiments, but the present study demonstrated that thymic clonal deletion played a major role in the prolongation of allograft survival after intrathymic injection of donor alloantigens.