| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
|
FJ
EXPRESS SUMMARY ARTICLE The Full-length version of this article is also available, published online February 10, 2006 as doi:10.1096/fj.05-4791fje. |
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
,1
,,1
* Immunobiology Research Center, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts, USA;
Department of Surgery, Medical University of Innsbruck, Austria;
Department of Pathology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, USA; and
¶ Instituto Gulbenkian de Ciência, Oeiras, Portugal
2Correspondence: Immunobiology Research Center, Beth Israel Deaconess Medical Center, Harvard Medical School, 99 Brookline Ave., Boston, MA 02215, USA. E-mail: fritz.bach{at}hms.harvard.edu
SPECIFIC AIMS
Heme oxygenase-1 (HO-1) expression and/or administration of the products of heme degradation by HO-1 have proved salutary in several phases of transplantation: suppression of ischemia-reperfusion injury, inhibition of acute (T cell-mediated) rejection, and in amelioration of chronic rejection. It was our goal to study the potential role of HO-1 in tolerance induction.
PRINCIPAL FINDINGS
1. Heme oxygenase-1 activity is required for induction of tolerance with donor specific transfusion (DST) + CD40L/CD40 blockade or DST alone
The combination of DST, given 7 days before transplantation, and anti-CD40L mAb (MR-1) resulted in 100% long-term survival of C57BL/6 hearts transplanted into Balb/c mice. While donor hearts that lacked HO-1 expression also survived long-term (>100 days), DST plus MR-1 failed to promote long-term graft survival when C57BL/6 hearts were transplanted into BALB/c HO-1-deficient (HO-1–/–) recipients (P<0.02 vs. HO-1+/+ recipients) (Fig. 1
).
|
Similarly, DST given on day –7 before transplantation, without further treatment, led to 50% of DBA/2 heart grafts surviving for > 100 days in B6AF1 recipients (P<0.005 vs. untreated control). Inhibition of HO activity by ZnPPIX administration to the recipient from day –8 (one day before DST) to day 6 after transplantation abrogated the tolerogenic effect of DST (day –7) with none (0/9) of the grafts surviving long-term (P<0.002 vs. DST alone, data not shown). These data show that HO-1 expression in the recipient is obligatory to sustain long-term graft survival and tolerance induction afforded by DST plus CD40/CD40L blockade or DST alone.
2. Induced HO-1 activity can synergize with DST in tolerance induction
When DST was given to B6AF1 recipients of DBA/2 hearts mice immediately after transplantation (day 0), these grafts were promptly rejected with a tempo similar to those transplanted into untreated controls (MST=10.3±0.8). Induction of HO-1 expression by CoPPIX administration to the recipient from day –1 to day +13 post-transplant together with DST (day 0) prolonged graft survival significantly (P<0.001 vs. DST alone) with 7 of 8 (87.5%) grafts surviving long-term (>100 days). Induced HO-1 expression also promoted tolerance induction when DST was given on day –7, which by itself led to 50% long-term survival. Induction of HO-1 expression by CoPPIX administration plus DST (day –7) led to 100% (7/7) of the grafts surviving for > 100 days (P<0.001 vs. DST alone). CoPPIX treatment of the recipient without DST resulted in a significant prolongation of allograft survival, with 2 of 6 grafts surviving long-term (i.e., >100 days). The combined effect of DST (day 0) plus HO-1 in terms of achieving long-term survival (tolerance) was significantly greater than HO-1 induction alone (P<0.03).
3. HO-1 promotes donor-specific "peripheral dominant" tolerance to cardiac allografts
To assess whether up-regulation of HO-1 plus DST induced antigen-specific and "peripheral dominant" tolerance in recipients of long-term surviving DBA/2 (H-2d) cardiac allografts, B6AF1 (H-2b,k/d) recipients carrying a DBA/2 transplanted heart for >100 days were, with no further treatment, challenged with a second heart from 1) DBA/2 mice, 2) FVB (H-2q) third-party mice or 3) DBA/2 x FVB F1 mice (H-2d/q). All DBA/2 hearts survived indefinitely, all FVB hearts were rejected promptly, and all DBA/2 x FVB F1 grafts were accepted for >100 days. These observations indicate that antigen-specific, peripheral dominant tolerance was established since as second transplants DBA/2 hearts survived indefinitely while FVB hearts did not, and tolerance to H-2d was propagated to H-2q when the H-2q antigens were presented by the same antigen-presenting cells (Fig. 2
a).
|
4. Induction of HO-1 expression plus DST promotes generation of CD4+CD25+ regulatory T cells that are involved in maintenance of tolerance
Induction of HO-1 expression by CoPPIX combined with DST (day –7) led to a significant decrease in the number of CD4+ T cells (P<0.01 vs. controls) in the lymph nodes on day 14 post-transplantation of DBA/2 hearts to B6AF1 recipients.) However, among the remaining CD4+ T cells there was a significant increase in the percentage of CD4+CD25+ T cells compared with controls (P<0.05), which was paralleled by a significant increase in the expression of Foxp3 as well as increases in TGF-ß, IL-10, and CTLA4. In adoptive transfer experiments, depletion of the CD4+CD25+ cells from a cell population that otherwise transferred tolerance, removed the tolerizing effect (Fig. 2b
).
CONCLUSIONS AND SIGNIFICANCE
We extend the salutary role that HO-1 expression can have in organ transplantation. In two models of tolerance induction in mice, both reported to involve T regulatory cells, expression/activity of HO-1 in the recipient were critical. In the absence of HO-1, it was not possible to induce tolerance. In one case we transplanted C57BL/6 hearts to Balb/c recipients that received DST + MR-1 using either wild-type recipients or Balb/c recipients deficient in HO-1 (HO-1–/–). In recipients lacking HO-1 expression, this protocol, which was effective at inducing tolerance in wild-type recipients, failed to do so in the HO-1–/– recipients. Likewise, tolerance induction with DST (day –7) alone failed when HO-1 activity was blocked in the recipient with ZnPPIX. These data demonstrate that HO-1 activity is essential for tolerance induction in these protocols that are thought to be based on T regulatory cell function. We hypothesize that this key role for HO-1 relates to the generation of T regulatory cells, perhaps via the need for HO-1 expression in dendritic cells that stimulate Treg.
It appears that tolerance in our studies was also based on T regulatory cell function. Induction of HO-1 expression plus DST increased the percentage of peripheral CD4+CD25+ T cells among CD4+ T cells in B6AF1 recipients carrying DBA/2 cardiac transplants. Emergence of a regulatory function associated with the appearance of these CD4+CD25+ T cells is supported by the increased expression of Foxp3, a transcription factor functionally involved in the immunoregulatory effect of CD4+CD25+ T cells. That these CD4+CD25+ T cells played a role in the establishment of donor-specific tolerance of DBA/2 (H-2d) hearts transplanted into B6AF1 (H-2k/d,b) recipients treated with DST plus HO-1 induction is suggested by the following. "Tolerizing leukocytes" from B6AF1 mice that were carrying a DBA/2 allograft long-term (after DST + HO-1 induction) failed to induce rejection of a DBA/2 heart when adoptively transferred into nonlethally irradiated B6AF1 recipients. However, B6AF1 recipients did reject DBA/2 (H-2d) hearts when CD25+CD4+ T cells were depleted from the tolerizing leukocytes and the remaining cells were adoptively transferred into nonlethally irradiated B6AF1 recipients. These observations suggest that the ability of DST plus HO-1 to induce antigen specific peripheral dominant tolerance is sustained functionally by regulatory CD25+CD4+ T cells.
In addition to the need for HO-1 expression to obtain tolerance by these protocols, induction of HO-1 expression appears to have beneficial effects in terms of promoting the tolerogenic effect of DST given at the time of transplantation. Most striking was our observation that induction of HO-1 led to tolerance in combination with DST (day 0), which by itself did not lead to any long-term surviving hearts. These data show synergy between HO-1 and DST. While we have shown this only for DST, it is possible that a similar synergistic, or an additive, effect of HO-1 induction would be observed for other approaches that are only partially effective for inducing tolerance. As a possible explanation for these findings, we and others have shown that expression of HO-1 is essential for the action of several immunomodulatory molecules (including IL-10 and rapamycin) to exert their therapeutic effects.
Given these results, treatment to induce HO-1 expression should perhaps become an important component of a feasible strategy to achieve tolerance in allogeneic transplantation.
|
FOOTNOTES
1 These authors contributed equally to this paper. 
To read the full text of this article, go to http://www.fasebj.org/cgi/doi/10.1096/fj.05-4791fje;
This article has been cited by other articles:
|
|
 |
|
  M. A. Williams, T. Rangasamy, S. M. Bauer, S. Killedar, M. Karp, T. W. Kensler, M. Yamamoto, P. Breysse, S. Biswal, and S. N. Georas Disruption of the Transcription Factor Nrf2 Promotes Pro-Oxidative Dendritic Cells That Stimulate Th2-Like Immunoresponsiveness upon Activation by Ambient Particulate Matter J. Immunol., October 1, 2008; 181(7): 4545 - 4559. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. C. Lee, F. Bhora, J. Sun, G. Cheng, E. Arguiri, C. C. Solomides, S. Chatterjee, and M. Christofidou-Solomidou Dietary flaxseed enhances antioxidant defenses and is protective in a mouse model of lung ischemia-reperfusion injury Am J Physiol Lung Cell Mol Physiol, February 1, 2008; 294(2): L255 - L265. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 S. Zelenay, A. Chora, M. P. Soares, and J. Demengeot Heme oxygenase-1 is not required for mouse regulatory T cell development and function Int. Immunol., January 1, 2007; 19(1): 11 - 18. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
