Expression of MHC-I mRNA in peripheral blood lymphocytes as an early marker of acute rejection following skin transplantation in mice

Early prediction of acute rejection (AR) is important in clinical practice of organ and tissue transplantation. The aims of this study were to investigate the expression of major histocompatibility complex (MHC)-I and MHC-II genes in peripheral blood lymphocytes (PBLs) following skin grafting and whether their expression can be used as early markers for AR. Skin-grafted mice were selected as an animal model and PBL samples were collected daily for up to 2 weeks post-transplant. Full-thickness skin from the backs of C57BL/6 mice (H-2b) was transplanted onto that of BALB/c mice (H-2d) in allograft group (H-2b to H-2d) and in syngeneic graft group (H-2d to H-2d). The expression levels of MHC-I (H-2K, H-2D) and MHC-II (H-2Ia, H-2Ie) mRNAs were examined using real-time PCR. The histopathological changes of graft biopsies were also analyzed with hematoxylin-eosin staining. The real-time PCR analysis showed that MHC-I and MHC-II mRNA levels were increased in a bimodal distribution pattern during AR in allograft group, whereas no significant changes were detected in syngeneic graft group. The level of H-2K mRNA was significantly increased at day 5 post-transplants compared with those pre-transplant controls (p < 0.01). This increase was detected 5-6 days earlier before graft rejection observed macroscopically. H-2K mRNA level was increased significantly in 93.8% of mice (61/65) in allograft group. These results indicate that the expression of MHC-I and MHC-II mRNAs is up-regulated in PBLs during AR. Especially, the expression of H-2K mRNA can be used as an early marker for AR.