FLOW CYTOMETRIC ANALYSIS OF CHIMERISM IN THE RAT TOLERANT TO A RENAL-ALLOGRAFT

Background. Chimerism, produced by the two-way migration of cells betw een graft and host, is a proposed mechanism by which tolerance occurs. The appearance of donor/recipient chimeras in tolerant ACI to Lewis r at heterotopic renal transplants was assessed in peripheral blood leuk ocytes using how cytometry after staining with monoclonal antibodies. Materials and methods. ACI and Lewis rats were used as donor and recip ient, respectively, after Rapamycin and Cyclosporin immunosuppression with or without donor blood or bone marrow transfusion. ACI and Lewis animals were also used for isograft and single-kidney controls. Animal s were sacrificed at various time points after initial operation, Flow cytometry was performed on isolated peripheral blood leukocytes at sa crifice. Histologic and functional data were also obtained. The monocl onal antibody panel included RT1(a) (ACI, MMC I) combined with CD2, CD 4, CD8, CD16, and CD25 or RT1(a,c) (bone marrow chimeras). Results. RT 1(a)+, CD8+ cells were transiently present in the peripheral blood leu kocytes of Lewis recipients with the exception of allogeneic bone marr ow recipients. No significant number of RT1(a)+, CD16+ (''dendritic'' cell-line) chimeras was seen. Veto cells (RT1(a,c)+) were transiently present in the bone marrow recipients, but they did not lead to improv ed outcome. Furthermore, no correlation was made between histologic to lerance and any of these donor-derived cells, Conclusion. Donor/recipi ent chimerism, and the veto cell phenomenon are not operational tolera nce mechanisms in this stringent model of ACI to Lewis rat renal trans plantation. (C) 1998 Academic Press.