Analysis of MHC class II expression on circulating T cells by flow cytometry in patients with acute rejection following solid organ transplantation

Aim: Following organ transplantation, acute steroid resistant graft rejecti on is one of the main predictors for long-term graft function. The developm ent of new noninvasive diagnostic methods can be helpful for diagnosis and follow-up of episodes of acute graft rejection. Patients and Study Design: Peripheral lymphocytes obtained during serial blood drawings from 206 diffe rent patients after kidney, heart or liver transplantation were analyzed fo r HLA-DR expression on CD8+T cells by two-color now cytometry, Patients wer e investigated during stable course as well as during episodes of graft rej ection or infection. Results: In liver-grafted patients without evidence fo r rejection or infection, the frequency of circulating HLA-DR+ CD8+ T lymph ocytes remained constant over time. The type of immunosuppressive treatment used (Tacrolimus or CyA with or without ATG) had no influence on the HLA-D R expression pattern observed. In contrast, a significant increase in HLA-D R expression was observed during acute biopsy-proven graft rejection. The t ime course of HLA-DR expression paralleled the clinical response of the ind ividual patient to antirejection treatment. In contrast to patients after l iver transplantation, in kidney or thoracic organ graft recipients with acu te graft rejection the increase in HLA-DR expression failed to reach statis tical significance. HLA-DR expression on CD8+ T cells was not specific to e pisodes of rejection; an increase in HLA-DR+ CD8+ T cells was also detectab le during episodes of bacterial or viral infection. Conclusion: In liver graft recipients the analysis of HLA-DR expression on CD8+ T cells is a sensitive but nonspecific marker for immune activation an d could be useful for monitoring of anti rejection therapy.