Apoptosis is involved in acute cardiac allograft rejection in rats

Apoptosis and acute cellular rejection in human heart transplants

INTRODUCTION AND OBJECTIVES

Apoptosis has been implicated in the pathophysiology of various forms of heart disease. Acute cellular rejection leads to morbidity after heart transplantation and invasive techniques are needed for its diagnosis. We investigated the presence of cardiomyocyte apoptosis in transplanted hearts, its progression, its relationship with rejection, and the possibility that serological markers of apoptosis can be used to detect rejection noninvasively.

METHODS

Overall, 130 endomyocardial biopsies obtained sequentially from 14 consecutive patients during the first 6 months following heart transplantation underwent histochemical analysis. The degree of acute rejection was determined, myocyte apoptosis was assessed using the TUNEL method, and caspase-3 activity was measured. In the first 10 patients, soluble Fas, tumor necrosis factor-alpha (TNFα) and interleukin 6 levels were determined in serum collected at biopsy.

RESULTS

Apoptotic cells were detected in 81.5% of biopsies. No significant correlation was found between the apoptotic index and either the degree of rejection or the time from transplantation; there was only a trend to higher values during prolonged episodes of rejection, which did not reach statistical significance. An inverse correlation was observed between the degree of rejection and the TNFα level (rs=-0.33; P=.003). There was no correlation with any other variable.

CONCLUSIONS

Cardiomyocyte loss due to apoptosis was observed in transplanted hearts, but no correlation was observed with either acute rejection or the time from transplantation. Our findings suggest there could be an inverse correlation between rejection and the serum TNFα level. No serum parameter evaluated was regarded as suitable for the noninvasive diagnosis of acute rejection.

Apoptotic cell death during accelerated rejection in sensitized rat recipients of cardiac allografts

Accelerated rejection due to host sensitization to major histocompatibility complex antigens is a critical problem in clinical organ transplantation in patients who have previously received an organ transplant, experienced acute rejection episodes, received blood transfusions, or been pregnant. The precise pathologic mechanisms underlying accelerated rejection have not been characterized. Herein, we describe apoptosis during T- and B-cell-driven accelerated rejection of cardiac allografts in presensitized recipients. In an established accelerated rejection model, Lewis rats were sensitized to skin grafts from Wistar-Furth rats; after 7 days, they received Wistar-Furth hearts. These grafts were rejected within 24 hours posttransplantation compared with 10 days in nonsensitized recipients (acute rejection, n = 5). Apoptosis was observed during accelerated rejection of cardiac allografts but not in naïve recipients of hearts, as demonstrated at DNA laddering and TUNEL (terminal deoxynucleotide transferase-mediated deoxyuridine triphosphate nick-end labeling) assay. Apoptosis was discovered as a thus far unknown effector mechanism in accelerated cardiac transplant rejection that accompanies combined cellular and humoral immune alloreactivity. Apoptotic cell death in accelerated rejection and the cascade of upstream and downstream events leading to or resulting from this process should be considered critical steps in the pathogenesis of accelerated rejection.

Elevation of plasma granzyme B levels after acute myocardial infarction

BACKGROUND

Apoptosis is reported to play an important role in left ventricular (LV) remodeling after acute myocardial infarction (AMI). Granzyme B is a member of the serine esterase family, which has an important role in cellular apoptosis and extracellular matrix degradation.

METHODS AND RESULTS

Peripheral blood samples were obtained from 33 patients with a first-onset AMI treated by percutaneous coronary intervention (mean age: 61.4+/-8.7 years old) on days 1, 7 and 14 after onset. Plasma levels of tumor necrosis factor (TNF)-alpha, a soluble form of the Fas ligand (sFasL), and granzyme B were measured. TIMI grade 3 recanalization was accomplished in all patients within 12 h after onset. The LV end-diastolic volume index (LVEDVI) was calculated on day 1 and at 6 months after onset. Plasma levels of TNF-alpha, sFasL and granzyme B increased significantly on days 7 and 14 after onset of AMI. Stepwise multivariate regression analysis showed that the plasma granzyme B level on day 14 is a significant explanatory variable for changes in the LVEDVI.

CONCLUSIONS

Plasma levels of granzyme B increased after AMI, which might be an important factor in the progression of late LV remodeling after AMI.

Decreased endomyocardial RANKL expression in transplant coronary artery disease

Transplant-associated coronary artery disease (TxCAD) appears to be initiated by endothelial cell activation and inflammation involving inflammatory cytokines and chemokines. Osteoprotegerin (OPG) and receptor activator of nuclear Factor-kappaB ligand (RANKL) have been implicated in cardiovascular disease progression and we measured the expression of these mediators in serum and myocardial biopsies taken serially during the first year after heart transplantation (HTx), relating them to the development of TxCAD. Serum OPG as well as myocardial gene expression of RANK and OPG, but not RANKL, were highest early after HTx and declined progressively. Importantly, patients who develop TxCAD or experience episodes of acute rejection showed a lower myocardial RANKL expression throughout the first year after transplantation than patients without these complications. Our findings may suggest an unrecognized role RANKL in maintaining myocardial and/or endothelial integrity and suggest that RANKL should be further investigated as a parameter that may predict development of TxCAD.

Link between immune cell infiltration and mitochondria-induced cardiomyocyte death during acute cardiac graft rejection

Acute cardiac graft rejection (ACGR) is associated with cardiomyocyte apoptosis. We investigated the respective role of the Fas/FasL and mitochondrial permeability transition pore (mPTP) pathways in cardiomyocyte apoptosis accompanying ACGR. Heterotopic cardiac transplantations were performed in 7-9-week old C57BL6 or C3H mice. Wild type or Fas-deficient (lpr) mice underwent syngeneic (GS) or allogeneic (GA) transplantation, and received either saline or NIM811, a specific inhibitor of the mPTP. At day 5, we assessed ACGR by histology, cardiomyocyte apoptosis by caspase-3 activity and cytochrome c release, Ca(2+)-induced mPTP opening by a potentiometric approach, and expression of Fas, FasL, TNFalpha, perforin, granzyme using RT-PCR. Myocardial infiltration of CD8(+) T lymphocytes was performed by immunohistochemistry. Allogenic transplantation increased infiltration of inflammatory cells, upregulated FasL, perforin, granzyme, and TNFalpha, favored Ca(2+)-induced mPTP opening and increased caspase-3 activity and cytochrome c release in WT grafts. NIM811, but not Fas-deficiency, significantly reduced all these effects. NIM811 also limited infiltration of CD8(+) into WT and lpr transplants. These data suggest that the mPTP pathway plays a major role in cardiomyocyte apoptosis associated with ACGR. Inhibition of mPTP opening may attenuate cardiomyocyte apoptosis either directly or indirectly via a limitation of CD8(+) T-cell activation.

Early Inhibition of Caspase-3 Activity Lessens the Development of Graft Coronary Artery Disease

BACKGROUND

The role of apoptosis in the development of graft coronary artery disease (GCAD) is poorly understood. We have previously shown that early overexpression of the anti-apoptotic protein Bcl-2 lessens the development of GCAD. We hypothesized that early inhibition of apoptosis with a caspase-3 inhibitor would also lessen the development of GCAD.

METHODS

Heterotopic heart transplantation was performed in 4 groups of rats. Donor hearts were pretreated with 50 microg DEVD-CHO, a cell-permeable caspase-3 inhibitor, or vehicle. Recipient animals were pretreated with 1.7 mg/kg intraperitoneal DEVD-CHO or vehicle. Animals were treated with 7.5 mg/kg/d cyclosporine for 10 days to prevent acute rejection. On post-operative day 90, the animals were sacrificed and the transplanted hearts were assessed morphometrically for evidence of GCAD.

RESULTS

At 90 days, intimal proliferation was significantly higher in vehicle treated animals than in inhibitor treated animals. Moreover, the percentage of vessels with high-grade occlusion (>50%) was also lower in inhibitor treated animals.

CONCLUSIONS

Early inhibition of caspase-3 activity with cell-permeable DEVD-CHO lessens the development of GCAD. Caspase-3 inhibition may be a useful strategy for prevention of GCAD in clinical transplantation.

3-Deazaadenosine prevents leukocyte invasion by suppression of adhesion molecule expression during acute cardiac allograft rejection: Involvement of apoptotic cell death

BACKGROUND

In the initial phase after cardiac transplantation, mononuclear cells infiltrate the graft, initiating a relevant impulse for rejection. 3-Deazaadenosine (c3Ado), an analog of adenosine, has proven anti-inflammatory properties both in vitro and in vivo. We hypothesized that c3Ado can serve as a therapeutic tool to reduce cellular infiltration in cardiac allograft transplantation.

METHODS

Using the Wistar-Furth-to-Lewis rat cardiac allograft model, animals were treated with 5 mg c3Ado subcutaneously twice per day. Allografts of untreated animals served as controls. Grafts were harvested on Days 1, 3 and 6 after transplantation for further examination (n = 4 per group and timepoint).

RESULTS

Immunohistochemical examination of c3Ado-treated grafts revealed up to 80% reduction of infiltrating major histocompatability complex (MHC) II-positive cells and T-cell-receptor-positive cells (R73) as well as ED1-positive monocytes and macrophages at Days 3 and 6 after transplantation. Adhesion molecule (ICAM-1 and VCAM-1) expression at Days 1 and 3 was almost completely abolished in c3Ado-treated grafts. However, c3Ado treatment did not prevent apoptotic cell death (TUNEL assay, DNA laddering) at Day 6, nor did it prolong allograft survival. As in controls, grafts were rejected at Day 7.

CONCLUSION

c3Ado significantly reduces graft infiltration by preventing leukocyte invasion, most likely through suppression of adhesion molecule expression. Although graft survival was not prolonged, treatment with c3Ado may still serve as a strategy to protect hearts from early damage after transplantation. Further studies will show whether peri-operative use of c3Ado can bridge the critical phase after transplantation when standard immunosuppression is not yet completely efficacious.

Mitochondrial permeability transition in cardiomyocyte apoptosis during acute graft rejection

Evidence indicates that acute cardiac graft rejection is associated with cardiomyocyte apoptosis. Mitochondrial permeability transition (MPT) induces apoptotic cell death. We sought to determine whether MPT might play a role in cardiomyocyte apoptosis in the rat model of heterotopic cardiac transplantation. Syngenic and allogenic transplantations were performed, and both native and grafted hearts were harvested 3 or 5 d after transplantation for detection of acute rejection, assessment of Ca(2+)-induced MPT, and myocardial apoptosis by TUNEL staining and caspase 3 activity. Allogenic grafts developed severe acute rejection at day 5 with concomitant cardiomyocyte apoptosis (apoptotic index: 7.1 +/- 1.0% vs. 1.0 +/- 0.2% in syngenic hearts, and caspase 3 activity: 38 +/- 25 vs. 5 +/- 9 nmol/mg, in allogenic vs. syngenic grafts, respectively). At day 5, Ca(2+)-induced MPT was dramatically altered in allogenic when compared with syngenic grafts (mean Ca(2+) overload averaged 0 +/- 20 vs. 280 +/- 30 microM in allogenic and syngenic grafts, respectively). NIM811, a nonimmunosuppressive derivative of cyclosporin A (CsA), that specifically inhibits the MPT pore, did not alter acute rejection, but significantly delayed Ca(2+)-induced MPT pore opening, attenuated caspase 3 activity and cardiomyocyte apoptosis in allogenic grafts. This suggests that mitochondrial permeability transition pore opening may play an important role in cardiomyocyte apoptosis associated with acute cardiac graft rejection.

Lesions of T-cell-mediated kidney allograft rejection in mice do not require perforin or granzymes A and B

Organ allograft rejection is strongly associated with the presence of alloreactive cytotoxic T cells but the role of cytotoxicity in the pathologic lesions is unclear. Previous studies showed that the principal lesions of kidney rejection - interstitial infiltration, tubulitis, and endothelial arteritis - are T-cell-dependent and antibody-independent. We studied the role of cytotoxic granule components perforin and granzymes A and B in the evolution of the T-cell-mediated lesions of mouse kidney transplant rejection. By real-time RT-PCR, allografts rejecting in wild-type hosts at days 5, 7, 21, and 42 showed massively elevated and persistent expression of perforin and granzymes A and B, but evolution of tubulitis and arteritis did not correlate with increasing granzyme or perforin expression. Allografts transplanted into hosts with disrupted genes for perforin or granzymes A and B showed no change in tubulitis, arteritis, or MHC induction. Thus the development of the histologic lesions diagnostic of T-cell-mediated kidney transplant rejection are associated with but not mediated by perforin or granzyme A or B. Together with previous graft survival studies, these results indicate that the granule-associated cytotoxic mechanisms of T cells are not the effectors of T-cell-mediated allograft rejection.

Bcl-2-mediated inhibition of apoptosis in rat cardiac allografts worsens development of graft coronary artery disease

BACKGROUND

We hypothesized that adenovirally mediated Bcl-2 transfection of donor hearts would reduce the apoptosis that occurs during acute rejection while worsening the development of chronic graft coronary artery disease (GCAD).

METHODS

PVG donor hearts were treated with either AdvBcl-2 or AdvNull virus before heterotopic transplantation into ACI rats. Bcl-2 expression was assessed on post-operative day 4 (POD) 4 by western blot. Apoptosis was measured using (99m)Technetium-bound-annexin V imaging and caspase 3 activity assay. Allograft survival was determined in a separate cohort of animals. Long-term-treated animals were then assessed for measures of GCAD on POD 90.

RESULTS

Western blot analysis showed upregulation of Bcl-2 expression in AdvBcl-2-treated hearts. (99m)Tc-annexin V images demonstrated decreased uptake in the AdvBcl-2 group (1.41 +/- 0.33% vs 1.94 +/- 0.37%, p = 0.026). Caspase 3 activity was also significantly lower in this treatment group (0.112 +/- 0.032 vs 0.204 +/- 0.096, p = 0.049). Allograft survival was similar in both groups, respectively (7.7 +/- 1.2 vs 6.8 +/- 1.5 days, p = 0.340). GCAD, as determined by percent luminal narrowing (5.9 +/- 6.1% vs 1.6 +/- 1.5%, p = 0.039), intima-to-media ratio (5.1 +/- 5.1% vs 1.5 +/- 1.7%, p = 0.040) and percent of affected vessels (15.1 +/- 9.9% vs 5.3 +/- 4.4%, p = 0.009), was higher for the AdvBcl-2 group.

CONCLUSION

Treatment of cardiac allografts with AdvBcl-2 resulted in a reduction of apoptosis that did not significantly improve short-term graft survival, but worsened chronic GCAD.

Gene expression during acute allograft rejection: novel statistical analysis of microarray data

High-throughput microarrays promise a comprehensive analysis of complex biological processes, yet their applicability is hampered by problems of reproducibility and data management. The current study examines some of the major questions of microarray use in a well-described model of allograft rejection. Using the Brown Norway to Lewis heterotopic heart transplant model, highly purified RNA was isolated from cardiac tissue at postoperative days (POD) 3, 5 and 7 and hybridized onto Affymetrix U34A microarrays. Using the log average ratio (LAR), changes in gene expression were monitored at each timepoint and p-values generated through statistical analysis. Microarray data were verified for 13 significant transcripts using RT-PCR. Of the 8800 transcripts studied, 2864 were increased on POD 3, 1418 on POD 5 and 2745 on POD 7. Verifying previous studies, many up-regulated genes appeared to be associated with the inflammatory process and graft infiltrating cells. Down-regulated transcripts included many novel molecules such as SC1 and decorin. LAR analysis provides a useful approach to analyze microarray data. Results were reproducible and correlated well with both RT-PCR and prior studies. Most importantly, these results provide new insights into the pathogenesis of acute rejection and suggest new molecules for future studies.

Zinc chloride-mediated reduction of apoptosis as an adjunct immunosuppressive modality in cardiac transplantation

BACKGROUND

Zinc (Zn) blocks caspase-3 activation in cardiac allografts and therefore may synergistically decrease apoptosis along with cyclosporine (CsA), which inhibits mitochondrial release of cytochrome c. Simultaneous treatment of rat recipients of heterotopic heart transplants with zinc chloride (ZnCl(2)) thus may allow lower doses of CsA for immunosuppression.

METHODS

PVG (RT1(c)) rat hearts were transplanted heterotopically into the abdomen of ACI (RT1(a)) rats. Group 1 (n = 15) rats received no treatment. Group 2 rats (n = 8) received 2 mg/kg/day CsA (sub-therapeutic dose) by oral gavage. Group 3 rats (n = 9) received 2 mg/kg/day oral CsA in addition to 1 mg/kg/day sub-cutaneous ZnCl(2) delivered by osmotic pump. All rats were imaged using Annexin V-bound (99m)Technetium ((99m)Tc-Annexin V) on post-operative Day 4 and subsequently killed. Annexin V avidly binds apoptotic cells in vivo. Region of interest per whole body (WB) data were calculated using the images. The allograft survival study was conducted with n = 11, 6, and 5 in control, CsA, and CsA+Zn groups, respectively. Finally, percentages of allografts that reached tolerance were measured in both CsA-only and CsA+Zn groups (n = 8 each).

RESULTS

Zinc chloride had an additive effect with CsA on apoptotic blockade and graft survival. The regions of interest per WB uptake of (99m)Tc-Annexin V were 2.43% +/- 0.37%, 2.08% +/- 0.52%, and 1.49% +/- 0.29%*, and acute survivals were 6.4 +/- 1.7, 7.2 +/- 2.1, and 11.2 +/- 2.5* days for control, CsA, and CsA+Zn groups, respectively (*p < 0.001 vs controls). In addition, 87.5% of allografts became tolerant and survived for 90 days in the CsA+Zn group compared with only 37.5% in the CsA-only group (p = 0.049).

CONCLUSION

Zinc-mediated reduction of apoptosis served as an effective adjunct immunosuppressive therapy to CsA in a rat model of cardiac transplantation.

In vivo imaging of acute cardiac rejection in human patients using (99m)technetium labeled annexin V

Annexin V binds phosphatidylserine moieties on apoptotic cells. This study reports the initial experience at Stanford University Medical Center with 99mTc-labeled annexin V imaging as a noninvasive measure of apoptosis in acute cardiac rejection. Ten cardiac transplant patients had 99mTc Annexin V imaging and endomyocardial biopsy (EMB) performed within 24 h. No complications related to 99mTc annexin V administration occurred. Eight patients had ISHLT grade of acute rejection of 1A or less. Five patients had two or more areas of uptake noted in the right ventricle on imaging studies. Two of these patients had positive biopsies: one patient had grade 2 rejection with two focal uptake areas and another had grade 3A rejection with three foci. An additional five patients had either one or zero hot spot areas and corresponding negative EMBs. 99mTc-annexin V appears to be well tolerated and may identify patients with acute cardiac rejection.

Cell death in the heart

The role of apoptosis in cardiac disease remains controversial. Much of the apoptosis detected, by chemical or molecular means, reflects inflammatory reaction and responding blood cells rather than myocytes, though their apoptosis in situ may exacerbate a bad situation, and their direct action against myocytes has not been excluded definitely. Myocyte apoptosis may reflect end-stage cardiac failure rather than causing it. If this is the case, then preventing apoptosis so that the cells can undergo necrosis does not accomplish much. Apoptosis is a consistent and important finding in many forms of cardiovascular disease. As determined by ultra-structure, apoptosis is common in cardiomyocytes, fibroblasts, vascular endothelial cells, and smooth muscle cells in cardiovascular disease of many origins. (62) Even though smooth muscle cells in atheromatous plaques appear to be necrotic,l it is likely that this is an evolved situation of apoptotic cells that were not removed. Given the prevalence of apoptotic processes in diseased heart and the very limited capacity of this organ to repair itself, (56) it is appropriate and justified to continue to explore the significance of apoptosis in cardiac disease and, above all, to explore the use of antiapoptotic agents in acute situations. Researchers must pay explicit attention to how they document cell death and in what tissues or cells it occurs. Otherwise, clinicians risk being deluded by preservation of morphology in nonfunctional cells and by confusion of what happened and where death occurred in the sequence of causality. Cell death in the heart is a matter of substantial theoretical and practical concern. A major problem in analyzing it is that, although apoptosis may be demonstrated easily in myocytes, particularly embryonic myocytes, under conditions of culture, interpretation is much more complex in an intact organ. The first issue is one of timing. In situations of severe, acute loss of cells, such as in an infarct, apoptotic cells may not be cleared rapidly and may progress to a more oncotic or necrotic morphology. Second, in situations of inflammation, biochemical or molecular techniques may confound apoptosis of inflammatory cells with apoptosis of myocytes. Third, priorities in the sequence of apoptosis differ between large, generally nonmitotic cells with massive cytoplasm (as differentiated myocytes) and small mitotic cells in culture, which usually are studied. The appearance and many markers of physiological cell death may differ from the most widely recognized forms of apoptosis, including late collapse of the nucleus and primacy of lysosomal or other proteases as opposed to caspases. Investigators should always strive to establish multiple criteria for apoptosis, with good documentation of timing and cell type. When these factors are taken into consideration, it seems that aggressive action against apoptosis may be of value in acute situations, such as infarct, in which buying short increments of time may reduce damage. In more chronic situations, much of the apoptosis detected derives from invading lymphocytes, mast cells, or other cells relating to inflammation. The apoptosis of these cells may exacerbate an already difficult situation, and intervention may prove of value. Otherwise, apoptosis of myocytes is more typically an end-stage situation, and it is more fruitful to alleviate the problem before this stage is reached.

Apoptosis in cardiac transplant rejection

Apoptosis occurs in human cardiac allograft rejection and may occur with all degrees of rejection and even in its absence. The prevalence and severity of apoptosis is determined predominantly by the intensity of macrophage infiltration and may be mediated by NO-related mechanisms. Apoptosis of interstitial, endothelial, and inflammatory cells is also present in heart allografts and may influence the degree and extent of vascular injury contributing to allograft rejection. Ongoing apoptosis of inflammatory cells suggests an immunoregulatory role. Studies of the involvement of NO in myocyte damage and Fas-FasL interactions in peripheral tolerance have raised the exciting possibility that these pathways can be exploited in a beneficial way. Further understanding of the role of apoptosis and the cellular and biochemical mechanisms that are involved in cardiac myocyte death and in inflammatory, endothelial, and interstitial cell death may provide insights into therapeutic modalities to suppress allograft rejection and vasculopathy.

Apoptosis: the importance of nuclear medicine

Apoptosis is a genetically controlled, energy-dependent process which removes unwanted cells from the body. Because of its orderly progression, apoptosis is also known as programmed cell death or cell suicide. Once initiated, apoptosis is characterized by a series of biochemical and morphological changes involving the cytoplasm, nucleus and cell membrane. Cytoplasmic changes include cytoskeletal disruption, cytoplasmic shrinkage and condensation; prominent changes in the nucleus include peripheral chromatin clumping and inter-nucleosomal DNA cleavage (DNA ladder formation); and membrane changes include the expression of phosphatidylserine on the outer surface of the cell membrane and blebbing (resulting in the formation of cell membrane-bound vesicles or apoptotic bodies). These events allow the cell to digest and package itself into membrane-bound packets containing autodigested cytoplasm and DNA, which can then be easily absorbed by adjacent cells or phagocytes. An endogenous human protein, annexin V (molecular weight approximately 35,000), has an affinity of about 10(-9) M for phosphatidylserine exposed on the surface of apoptotic cells. Annexin V can be labelled with radionuclides such as iodine or technetium, or positron emitting agents. Experimental studies in cells confirm that fluorescence and 99Tc(m)-labelled annexin have comparable affinity for apoptotic cells. In vivo studies with 99Tc(m)-labelled annexin confirm that radiolabelled annexin V can be used to image apoptotic cells/tissues in vivo. In this article, we review experimental data using annexin V imaging and discuss its possible future use to identify apoptosis in vivo.

Alloimmune-mediated apoptosis: comparison in mouse models of acute and chronic cardiac rejection

BACKGROUND

The purpose of the present study was (1) to compare apoptotic activity in models of acute and chronic rejection and (2) to study the cellular distribution of parenchymal versus inflammatory cell apoptosis.

METHODS

Heterotopic cardiac mouse transplantation (CBA into C57BL/6) was used to produce allografts undergoing acute (day 7, untreated recipients, n=6) or chronic (day 55, anti-CD4/8 for 28 days, n=6) rejection. As references, we used 55-day isograft controls (n=5) and native hearts (n=6). To assess apoptotic activity, we quantified DNA laddering (32P incorporation), DNA fragmentation (antinucleosome ELISA), and caspase-1 transcript levels (32P-reverse transcriptase-polymerase chain reaction). To localize apoptosis, we performed terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling.

RESULTS

DNA laddering and nucleosome levels were increased in allografts undergoing acute or chronic rejection when compared with both controls. Both parameters were twofold higher in acutely compared with chronically rejecting hearts. Caspase-1 transcript levels were increased in acutely (P<0.0001) and chronically rejecting hearts (P=0.004). Acutely rejecting grafts had more terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling-positive nuclei (53+/-3 nuclei/high-powered field) than chronically rejecting grafts (9+/-1 nuclei/high-powered field, P<0.0001), but the distribution between graft-infiltrating inflammatory cells and myocytes was similar. Vascular cells undergoing apoptosis were infrequent in both forms.

CONCLUSION

Using four separate indices, apoptotic activity is more pronounced in cardiac allografts undergoing acute compared with chronic rejection. This reflects, in part, the degree of alloimmune response. However, we speculate that the contributions of apoptosis to various forms of rejection are multifactorial. The long-term outcome to the graft may depend upon the magnitude, timing, and target of programmed cell death.