Microchimerism in female renal transplant recipients from male donors

Microchimerism in 23 female renal transplant recipients from male donors was studied using nested polymerase chain reaction (nPCR) and fluorescence in situ hybridization (FISH) to detect Y-chromosome. nPCR was a sensitive and specific assay enabling a detection rate of 1/10(6) male/female cells, compared with a sensitivity of 1/10(2) by standard PCR (sPCR). None of the 23 patients with a male allograft demonstrated Y-chromosome using sPCR. In contrast, 1 3 (56.5%) patients demonstrated Y-chromosome with nPCR. Of 9 patients proven to have microchimerism by nPCR, only 3 also demonstrated Y-chromosome using FISH. The existence of B cells and CD8 cells in donor chimeric cells were proved by separation with Dynabeads class I and class II. Dynamic changes of microchimerism occurred in 4 of 5 patients. Four patients were proven to have microchimerism within a year of transplantation and the microchimerism later disappeared in 3, although the sequential change was variable in individual patients. There was no correlation between microchimerism and patients'clinical factors such as donor-specific blood transfusion, HLA matching, immunosuppression, past history of acute rejection and chronic rejection. The degree of microchimerism in renal transplant recipients was relatively low, and its existence did not seem to be compatible with long-term graft acceptance. However, further studies are required to elucidate the immunological mechanism of microchimerism, and it might be an important clue to immunological tolerance.