[The mechanism of donor specific unresponsiveness in renal transplant recipients]

A study was conducted to clarify the mechanism of donor specific immunological unresponsiveness in renal transplant recipients with a well functioning kidney, since this might provide a clue to the nature of donor specific immunosuppression. Peripheral blood lymphocytes (PBL) were obtained from three renal transplant recipients, the donors (mother), the fathers and healthy volunteers as 3rd party and used in the present study. PBL from one of the three renal transplant recipients, which were donor specific unresponsive in MLR (Mixed Lymphocyte Reaction) and CML (Cell Mediated Lympholysis), suppressed the MLR, CML and synthesis of IL-2 from 3rd party PBL in a double chamber assay only when stimulated by the donor PBL. This suppression was abolished by the treatment with CD3 or CD8 antibodies and complement. RT-PCR was performed to investigate the suppressive effect of the recipient's PBL on IL-2 mRNA expression. In the double chamber MLR, expression of IL-2 mRNA by the PBL from 3rd party was also suppressed only when the recipient's PBL were stimulated by the donor PBL. These results indicate that one of the mechanisms responsible for donor specific immunological unresponsiveness is the presence of donor specific suppressor T cells in recipient's PBL and that these cells project suppressive effect on lymphocytes by producing a humoral suppressive factor(s) that suppress the expression of the IL-2 mRNA only when stimulated by donor PBL.