Differences in lymphocyte gene expression between tolerant and syngeneic liver grafted rats

✍ Scribed by Masayuki Fujino; Yusuke Kitazawa; Mikiko Kawasaki; Naoko Funeshima; Hiromitsu Kimura; Toshiharu Nakajima; Hirohisa Saito; Xiao-Kang Li

• Publisher: John Wiley and Sons
• Year: 2004
• Tongue: English
• Weight: 363 KB
• Volume: 10
• Category: Article
• ISSN: 1527-6465
• DOI: 10.1002/lt.20082

✦ Synopsis

Induction of tolerance to allogeneic donor grafts is a clinically desirable goal in bone marrow and solid organ transplantation. We have taken the advantage of DNA microarray technology to investigate gene expression mechanism in regulatory cells. In the present study, using a tacrolimus (FK506) induced tolerance of the fully mismatched liver allograft rat model, we demonstrated that, in contrast with peripheral blood lymphocytes (PBLs) from syngeneic recipients, PBLs taken from tolerant recipients 100 days after transplantation were able to suppress the in vitro proliferation of allogeneic PBLs and to prolong the survival of second syngeneic recipients. We also compared messenger RNA profiles in PBLs from tolerant recipients with those from syngeneic recipients using a DNA microarray with probe sets corresponding to more than 8000 rat genes. There were 96 up-regulated and 103 down-regulated genes in the tolerant recipients. In the up-regulated group, there were 76 known genes and 20 expressed sequence tags (ESTs). In the down-regulated groups, there were 87 known genes and 16 ESTs. Our data indicated that FK506 treatment induced tolerance and expansion of regulatory cells and the DNA microarray technology was useful for this application and provided many informative insights into the mechanism of lymphocyte regulation. (Liver Transpl 2004;10:379 -391.)

T he possible mechanisms of transplantation tol- erance include clonal deletion of allo-reactive cells, clonal anergy, ignorance or helpness, exhaustion, cell-mediated suppression, 1 and what has been termed as "infectious" tolerance, 2 based on the ability of transferred T cells to propagate and impose tolerance in new cohorts of test animals. Recently, considerable evidence has suggested the existence of regulatory T cells that prevent autoimmunity and maintain transplantation tolerance. 3,4 Studies of the mechanisms underlying this tolerance indicate immune regulation as the major determinant, with CD4ϩ T lymphocytes from tolerant hosts inhibiting rejection of donor-specific allografts after adoptive transfer into sets of test rat recipients. 5 In contrast, the clonal exhaustion-deletion is thought to be the seminal mechanism of tolerance and participated with the donor leukocyte chimerism-associated mechanisms of acquired tolerance. 6 -8 Although the elucidation of clonal exhaustion-deletion has been unclear, it may be possible that regulatory T cells are involved with this mechanism in part.

The phenotype of these regulatory T cells has been further refined, and CD4ϩCD25ϩ CD45RB low T cells are now considered the principle components. 4,9,10 These cells have been shown capable of regulating CD4ϩCD25-or CD4ϩCD45RB high in nontolerant cells both in vitro and in vivo, preventing the onset of autoimmunity and gut immunopathology. [11][12][13][14] They have also been shown capable of suppressing in vitro proliferation and INF-␥ secretion by CD8ϩ T cells. 15 Recently, Graca et al. 16 showed that both CD4ϩCD25ϩ and CD4ϩCD25-cells from tolerant mice could mediate suppression. In that study, they concluded that regulatory cells in both populations were involved in suppression, perhaps acting together.

Previous studies had shown that only the CD4ϩD25ϩ cells from tolerant animals were important for regulation. 21,22 In agreement with Graca et al., Chiffoleau et al. 17 demonstrated that transplantation tolerance was transferable with splenic and thymic CD4ϩCD25ϩ cells, and also in 50% of cases with splenic CD4ϩ CD25-cells. It was shown that CD25 might be a