Prolonged Allograft Survival in TNF Receptor 1-Deficient Recipients Is Due to Immunoregulatory Effects, Not to Inhibition of Direct Antigraft Cytotoxicity

Abstract

TNF-α and lymphotoxin (LT)α have been shown to be important mediators of allograft rejection. TNF-R1 is the principal receptor for both molecules. Mice with targeted genetic deletions of TNF-R1 demonstrate normal development of T and B lymphocytes but exhibit functional defects in immune responses. However, the role of TNF-R1-mediated signaling in solid organ transplant rejection has not been defined. To investigate this question, we performed vascularized heterotopic allogeneic cardiac transplants in TNF-R1-deficient (TNF-R1−/−) and wild-type mice. Because all allografts in our protocol expressed TNF-R1, direct antigraft effects of TNF-α and LTα were not prevented. However, immunoregulatory effects on recipient inflammatory cells by TNF-R1 engagement was eliminated in TNF-R1−/− recipients. In our study, cardiac allograft survival was significantly prolonged in TNF-R1−/− recipients. Despite this prolonged allograft survival, we detected increased levels of CD8 T cell markers in allografts from TNF-R1−/− recipients, suggesting that effector functions, but not T cell recruitment, were blocked. We also demonstrated the inhibition of multiple chemokines and cytokines in allografts from TNF-R1−/− recipients including RANTES, IFN-inducible protein-10, lymphotactin, and IL-1R antagonist, as well as altered levels of chemokine receptors. We correlated gene expression with the physiologic process of allograft rejection using self-organizing maps and identified distinct patterns of gene expression in allografts from TNF-R1−/− recipients. These findings indicate that in our experimental system TNF-α and LTα exert profound immunoregulatory effects through TNF-R1.

Modulation of gene expression by alloimmune networks following murine heart transplantation

“…1a). The survival times observed in our experiments were similar to previously reported values (Corry et al 1973;Peugh et al 1986;Grusby et al 1993;Qian et al 1996;Saleem et al 1996;Chitilian and Auchincloss 1997;Exner et al 1999;Forster et al 1999;Mandelbrot et al 1999;Kishimoto et al 2000;Smiley et al 2000;Wasowska et al 2001;Finn et al 2001;McKee et al 2002). Due to the possibility that gene expression could change simply due to kinetic considerations, we used supervised methods (Cluster and GeneCluster) to arbitrarily classify the experimental recipients into three groups based on mean survival time (MST) as follows: (i) the rapid-rejection group has an MST of less than twice that of wild-type recipients of allogeneic grafts; (ii) the no-rejection group has an MST of >100 days, and (iii) the remaining recipients form the intermediate survival group.…”

The endogenous pro-resolving mediators lipoxin A4 and resolvin E1 preserve organ function in allograft rejection

“…Endogenous levels of LXA 4 correlated with the severity of both airway and vascular rejection, suggesting a pivotal role for this counter-regulatory lipid mediator in regulating immune-mediated attack of the transplanted organ. LXA 4 is a potent regulator and stop signal for PMN migration and activation [23, 24] and here decreased TNFα-initiated activation, which is pivotal to early events in organ rejection [14]. In addition, an LXA 4 stable analog and ALX-tg mice provided the means for investigating roles for the LXA 4 –ALX axis in vivo during solid organ transplant rejection.…”

“…Interleukin-8, IL-1β and LTB 4 have been implicated in the pathophysiology of lung allograft rejection [27]. In addition, TNFα signaling is an important mediator of acute and chronic cardiac allograft rejection [14]. TNFα increases leukocyte calcineurin activity and activates PMN [30].…”

“…Murine hearts were transplanted heterotopically as previously described [14]. Hearts were harvested and donor aorta anastamosed to recipient vena cava.…”

Constitutive expression of the anti-apoptotic Bcl-2 family member A1 in murine endothelial cells leads to transplant tolerance

“…The proinflammatory cytokine TNF-α has been shown to be an important mediator of allograft rejection [28] with prolongation of allograft hearts survival being reported in recipient mice lacking the TNF receptor [29]. As over expression of A1, using retrovirus transduction, protected human ECs against TNF-α induced…”