COVID-19 in recent heart transplant recipients: Clinicopathologic features and early outcomes.

BACKGROUND: The impact of COVID-19 on heart transplant (HTx) recipients remains unclear, particularly in the early post-transplant period. METHODS: We share novel insights from our experience in five HTx patients with COVID-19 (three within 2 months post-transplant) from our institution at the epicenter of the pandemic. RESULTS: All five exhibited moderate (requiring hospitalization, n = 3) or severe (requiring ICU and/or mechanical ventilation, n = 2) illness. Both cases with severe illness were transplanted approximately 6 weeks before presentation and acquired COVID-19 through community spread. All five patients were on immunosuppressive therapy with mycophenolate mofetil (MMF) and tacrolimus, and three that were transplanted within the prior 2 months were additionally on prednisone. The two cases with severe illness had profound lymphopenia with markedly elevated C-reactive protein, procalcitonin, and ferritin. All had bilateral ground-glass opacities on chest imaging. MMF was discontinued in all five, and both severe cases received convalescent plasma. All three recent transplants underwent routine endomyocardial biopsies, revealing mild (n = 1) or no acute cellular rejection (n = 2), and no visible viral particles on electron microscopy. Within 30 days of admission, the two cases with severe illness remain hospitalized but have clinically improved, while the other three have been discharged. CONCLUSIONS: COVID-19 appears to negatively impact outcomes early after heart transplantation.

Repeat exposure to group A streptococcal M protein exacerbates cardiac damage in a rat model of rheumatic heart disease.

Rheumatic fever and rheumatic heart disease (RF/RHD) develop following repeated infection with group A streptococci (GAS). We used the Rat Autoimmune Valvulitis (RAV) model of RF/RHD to demonstrate that repetitive booster immunization with GAS-derived recombinant M protein (rM5) resulted in an enhanced anti-cardiac myosin antibody response that may contribute to the breaking of immune tolerance leading to RF/RHD and increased infiltration of heart valves by mononuclear cells. With each boost, more inflammatory cells were observed infiltrating heart tissue which could lead to severe cardiac damage. We also found evidence that both complement and anti-M protein antibodies in serum from rM5-immunized rats have the potential to contribute to inflammation in heart valves by activating cardiac endothelium. More importantly, we have demonstrated by electrocardiography for the first time in the RAV model that elongation of P-R interval follows repetitive boost with rM5. Our observations provide experimental evidence for cardiac alterations following repeated exposure to GAS M protein with immunological and electrophysiological features resembling that seen in humans following recurrent GAS infection.

Decrease in dendritic cells in endomyocardial biopsies of human dilated cardiomyopathy.

AIMS: Dendritic cells (DCs) are sentinels of the immune system-their role in myocardial disease is unknown as yet. We investigated their myocardial presence in human dilated cardiomyopathy (DCM). METHODS AND RESULTS: Endomyocardial biopsies from 72 patients with DCM (EF ∼30%), as well as myocardial specimens from 18 suicide or accident victims were immunohistochemically analysed for myeloid and plasmacytoid DCs, antigen-presenting cells (APCs), and other leucocytes; also tissue fibrosis and apoptosis were histologically quantified. The myocardial viral genome was identified through polymerase chain reaction, and patients underwent clinical follow-up in 3-6 months. We found myocardial DCs of all examined subtypes and maturation stages (fascin, CD11c, CD209, CD83, and CD304), as well as markers for APCs (HLA-DR and CD40) and T-cell activation (CD69) to be significantly decreased in DCM compared with controls. In contrast, regulatory T cells (the GITR epitope), apoptosis (by TUNEL reaction and immunostaining with BCL-2), and a DC chemokine receptor (CCR7) were overexpressed, while no significant differences were observed for macrophages (CD68). Immature myeloid and plasmacytoid DCs strongly correlated with endothelial progenitor cells (CD34), which were similarly reduced in DCM, and inversely correlated with fibrosis. Myeloid DCs were especially reduced in virus-positive biopsies, and their numbers correlated with positive change in EF (ΔEF) at follow-up. CONCLUSION: Myocardial DCs are reduced in heart biopsies of symptomatic DCM patients. Such a reduction correlates with an unfavourable short-term outcome in terms of EF, and could result from myocardial tissue damage, cellular death, and insufficient vascularization in chronic heart failure.

B cells in cardiac transplants: from clinical questions to experimental models.

After many years of debate, there is now general agreement that B cells can participate in the immune response to cardiac transplants. Acute antibody-mediated rejection (AMR) is the best defined manifestation of B cell responses, but diagnostic and mechanistic questions still surround AMR. Many complement dependent mechanisms of antibody-mediated injury have been elucidated. C5 has become a therapeutic target that may not just truncate complement activation, but also may tip the balance away from inflammation by altering macrophage function. Additional complement independent effects have been identified. These may escape diagnosis and progress to chronic graft injury. The function of B cell infiltrates in cardiac transplants is even more enigmatic. Nodular endocardial infiltrates that contain B cells and plasma cells have been described in protocol biopsies of cardiac transplants for decades, but an understanding of their significance is still evolving based on more critical morphological and molecular evaluation of these infiltrates. A range of infiltrates containing B cells has also been described in the epicardial fat in transplants with advanced chronic rejection. B cells have been observed in endocardial and epicardial tertiary lymphoid nodules, but their impact on antigen presentation or antibody production remains to be determined. Experimental models in small and large animals suggest that B cells could be essential for the formation of lymphoid nodules through cytokine production. Similarly, the role of proinflammatory adipokines in the formation or function of epicardial lymphoid nodules has not been studied. These clinical observations provide critical questions to be addressed in experimental models.

C4d analysis in endomyocardial biopsies of heart transplant patients: is there a correlation with hemodynamic data?

BACKGROUND: Endomyocardial biopsy (EMB) is the gold standard for immunologic follow-up to detect acute cellular rejection after cardiac transplantation. Conversely, protocols for the diagnosis and treatment of antibody-mediated rejection (AMR) are not well defined. Histologically, AMR is diagnosed by the presence of capillary damage associated with complement activation. The aim of this study was to correlate C4d expression of activated complement in EMB with hemodynamic compromise upon right heart catheterization. METHODS: Heart transplant patients underwent hemodynamic and histologic follow-up with EMB and right heart catheterization between January 2008 and December 2009 for a total of 491 procedures. The cardiac biopsy was evaluated for acute cellular and AMR by means of the presence of the C4d complement fraction. The histologic results were compared with hemodynamic data registered during right heart catheterization. RESULTS: Comparison of the hemodynamic data of subjects with versus without C4d positivity showed no significant difference. Furthermore, there was no significant difference comparing patients with versus without C4d positivity in the absence of significant acute cellular rejection episodes. (C4d-/ACR- vs C4d+/ACR-). The variation of each single hemodynamic parameter from its basal value (defined as the mean value in case of C4d-/ACR-) seemed to not be influenced by the presence of C4d+. CONCLUSIONS: In our experience, C4d has been routinely evaluated in the majority of EMBs. We could not demonstrate a significant correlation of C4d positivity with hemodynamic compromise. These findings suggest that significant allograft dysfunction is not related to C4d positivity. Therefore, the diagnosis of AMR is difficult to establish, because allograft dysfunction is 1 of the 3 fundamental criteria.

Outcomes of cardiac transplantation in highly sensitized pediatric patients.

Despite aggressive immunosuppressive therapy, pediatric orthotopic heart transplant (OHT) candidates with elevated pre-transplant panel reactive antibody (PRA) carry an increased risk of rejection and early graft failure following transplantation. This study has aimed to more specifically evaluate the outcomes of transplant candidates stratified by PRA values. Records of pediatric patients listed for OHT between April 2004 and July 2008 were reviewed (n = 101). Survival analysis was performed comparing patients with PRA < 25 to those with PRA > 25, as well as patients with PRA < 80 and PRA > 80. Patients with PRA > 25 had decreased survival compared with those with PRA < 25 after listing (P = 0.004). There was an even greater difference in survival between patients with PRA > 80 and those with PRA < 80 (P = 0.002). Similar analyses for the patients who underwent successful transplantation showed no significant difference in post-transplant survival between patients with a pre-transplant PRA > 25 and those with PRA < 25 (P = 0.23). A difference approaching significance was noted for patients with PRA > 80 compared with PRA < 80 (P = 0.066). Patients with significantly elevated pre-transplant PRAs at the time of listing have a significantly worse outcome compared to those with moderately increased PRA values or non-sensitized patients. Further study is necessary to guide physician and family treatment decisions at the time of listing.

[Heart transplantation. Pathology, clinical work-up and therapy]. / Herztransplantation. Pathologie, Klinik und Therapie.

Since the first heart transplantation in 1967, the procedure has become an established therapy in the treatment of terminal heart failure. Constant advances in the development of potent immunosuppressive drugs, as well as greater clinical experience and pathological diagnostics have improved patient survival dramatically. The first grading system for rejection was published in 1990 by the International Society for Heart and Lung Transplantation (ISHLT) and revised in 2004. The 2004 grading system comprises three grades of severity (1R, 2R, 3R), whereby the former grade 2 in the 1990 system has been incorporated in the new grade 1R. Recommendations are made for the histological diagnosis of acute antibody-mediated rejection using immunohistochemical staining against C4d and macrophages. To the present day, the pathological examination of endomyocardial biopsies remains the gold standard for post-transplant diagnostic procedures. Whether or not non-invasive diagnostic approaches (e.g. gene array profile analysis on leukocytes) can replace morphological investigations needs to be clarified in randomised, prospective clinical studies.

Expression of allograft inflammatory factor-1 (AIF-1) in acute cellular rejection of cardiac allografts.

BACKGROUND: To date, there are no good biomarkers for diagnosing and predicting the progression of cardiac allograft rejection. Previous studies have shown a correlation of allograft inflammatory factor-1 (AIF-1) to human cardiac allograft rejection; however these studies were limited in sample size and did not address whether AIF-1 could be used as a biomarker in diagnosing and predicting the progression of cardiac allograft rejection. METHODS: Using immunohistochemistry, AIF-1 expression was determined in cardiomyocytes (CMCs), mononuclear cells (MNCs) and Quilty lesions in 192 allograft endomyocardial biopsies and 37 heart specimens from nontransplant patients with diverse heart diseases. RESULTS: AIF-1 was found in both cardiac allografts and hearts with other cardiac diseases. In cardiac allografts, expression levels of AIF-1 in both CMCs and MNCs directly correlated with the severity of cardiac cellular rejection. AIF-1 expression was also elevated in Quilty B lesions, but not in Quilty A lesions. The rejection grade in subsequent biopsies increased in biopsies that had low-grade rejection with high CMC AIF-1 scores or Quilty B lesions. CONCLUSION: AIF-1 was expressed in both CMCs and MNCs in hearts with various adverse conditions including but not limited to heart transplantation. In cardiac transplantation, AIF-1 was associated with the severity of cardiac allograft rejection and Quilty B lesions, which could predict subsequent increases in rejection grade. Thus, AIF-1 shows promise that it can be a potential biomarker for cardiac allograft rejection.

Benefit of immune monitoring in heart transplant patients using ATP production in activated lymphocytes.

BACKGROUND: Balancing immunosuppression to prevent rejection while minimizing infection or drug toxicity risk is a major challenge in heart transplantation. Therapeutic drug monitoring alone is inadequate to measure the immune response. An immune monitoring (IM) assay (ImmuKnow; Cylex, Columbia, MD) performed on peripheral blood measures adenosine triphosphatase (ATP) release from activated lymphocytes and may predict the immune state. Therefore, we sought to determine the utility of IM in heart transplant recipients. METHODS: Between November 2005 and July 2008, 296 heart transplant recipients had a total of 864 IM assays performed at 2 weeks to 10 years post-transplant and were correlated with infection and rejection events that occurred within 1 month after IM testing. All patients received standard triple-drug immunosuppressive therapy with tacrolimus, mycophenolate mofetil and corticosteroids, without induction therapy. RESULTS: There were 38 infectious episodes and 8 rejection episodes. The average IM score was significantly lower during infection than steady state (187 vs 280 ng ATP/ml, p < 0.001). The average IM score was not significantly different during rejection when compared with steady state (327 vs 280 ng ATP/ml, p = 0.35). Interestingly, 3 of 8 rejection episodes were antibody-mediated rejections and had hemodynamic compromise and, for these, the mean IM score was significantly higher than for steady-state patients (491 vs 280 ng ATP/ml, p < 0.001). CONCLUSIONS: The non-invasive IM test appears to predict infectious risk in heart transplant patients. The association between high IM scores and rejection risk is inconclusive due to the small number of rejection episodes. Further studies with larger sample sizes for rejection episodes are required.

Recruitment of immune cells across atrial endocardium in human atrial fibrillation.

BACKGROUND: Although clinical studies have suggested a link between inflammation markers and atrial fibrillation (AF), it is still unclear whether local immunologic responses actually exist in human atria during AF. METHODS AND RESULTS: To address this point, human left appendages were obtained from 16 patients who underwent cardiac surgery (5 with sinus rhythm (SR) and 11 with AF) and subjected to immunohistochemical analysis. In all the AF specimens, adhesion and migration of CD45-reactive cells were consistently observed predominantly in the atrial endo- and subendomyocardium and more prominently than in SR. Most of them were immunologically active CD68-positive macrophages, whereas CD3-positive T cells infiltrated to a lesser extent. Scavenger-receptor A staining revealed maturation of macrophages not in the endocardium but in the midmyocardium, a gradient from endo- to midmyocardium. In the endocardium, along with adhesion molecules (intracellular adhesion molecule-1 and vascular cell adhesion molecule-1), a chemotactic protein-1, which facilitates the recruitment, was more abundantly expressed in AF than in SR. Cytokines including transforming growth factor-beta and interleukin-6 were frequently expressed by these macrophages. CONCLUSIONS: These observations collectively imply active adhesion and recruitment of macrophages across the endocardium in human fibrillating atria, thereby supporting the concept of local immunologic inflammatory responses around the atrial endocardium of AF.

Asymptomatic antibody-mediated rejection after heart transplantation predicts poor outcomes.

BACKGROUND: Antibody-mediated rejection (AMR) has been associated with poor outcome after heart transplantation. The diagnosis of AMR usually includes endomyocardial biopsy findings of endothelial cell swelling, intravascular macrophages, C4d+ staining, and associated left ventricular dysfunction. The significance of AMR findings in biopsy specimens of asymptomatic heart transplant patients (normal cardiac function and no symptoms of heart failure) is unclear. METHODS: Between July 1997 and September 2001, AMR was found in the biopsy specimens of 43 patients. Patients were divided into 2 groups: asymptomatic AMR (AsAMR, n = 21) and treated AMR (TxAMR with associated left ventricular dysfunction, n = 22). For comparison, a control group of 86 contemporaneous patients, without AMR, was matched for age, gender, and time from transplant. Outcomes included 5-year actuarial survival and development of cardiac allograft vasculopathy (CAV). Patients were considered to have AMR if they had > or = 1 endomyocardial biopsy specimen positive for AMR. RESULTS: The 5-year actuarial survival for the AsAMR (86%), TxAMR (68%), and control groups (79%) was not significantly different (p = 0.41). Five-year freedom from CAV (> or = 30% stenosis in any vessel) was AsAMR, 52%; TxAMR, 68%; and control, 79%. Individually, freedom from CAV was significantly lower in the AsAMR group compared with the control group (p = 0.02). There was no significant difference between AsAMR vs TxAMR and TxAMR vs control for CAV. CONCLUSIONS: Despite comparable 5-year survival with controls after heart transplantation, AsAMR rejection is associated with a greater risk of CAV. Trials to treat AsAMR to alter outcome are warranted.

Infiltration of macrophages through the atrial endocardium of inflammation-induced rats: contribution of fractalkine.

BACKGROUND: Inflammatory processes in the atria during systemic inflammation remain unclear, so this study tested the hypothesis that macrophages infiltrate the atrial myocardium mainly through the atrial endocardium with the contribution of fractalkine. METHODS AND RESULTS: Sprague-Dawley rats were injected with lipopolysaccharide (LPS) to simulate inflammation in the atria. Inflammation was immunohistologically assessed by the presence of macrophages. Macrophage infiltration was diffuse throughout the atrial myocardium after LPS injection. At an earlier phase after LPS injection, the number of macrophages dramatically increased, mainly in the atrial endocardium, and the expression of fractalkine protein was markedly increased by treatment with LPS in the atrial endocardium. The LPS-induced increase in atrial macrophage infiltration was significantly suppressed by neutralizing the fractalkine protein (P<0.01). CONCLUSIONS: In an experimental model of atrial inflammation, macrophages infiltrated the myocardium mainly through the atrial endocardium with the contribution of fractalkine. Inhibition of macrophage infiltration by suppressing chemokine expression could be a novel therapeutic approach to controling acute inflammation in the atria.

Successful treatment of cardiogenic shock caused by humoral cardiac allograft rejection.

The progress of immunosuppressive therapy has made heart transplantation the standard therapy for end-stage heart failure. However, humoral rejection of the cardiac allograft is still a challenging problem associated with high incidence of graft loss and patient mortality. The present patient developed profound cardiogenic shock requiring extracorporeal life support on the 8th day after heart transplantation. Endomyocardial biopsy revealed no cellular rejection, and complement component C4d was positively stained on the capillary endothelium. The patient was successfully treated with repeated plasmapheresis and administration of anti-CD20 monoclonal antibody, rituximab, as well as with steroid pulse and increased standard immunosuppressive medication.

Evolution of the inflammatory response in vertebrates: fish TNF-alpha is a powerful activator of endothelial cells but hardly activates phagocytes.

TNF-alpha is conserved in all vertebrate classes and has been identified in all taxonomic groups of teleost fish. However, its biological activities and its role in infection are largely unknown. Using two complementary fish models, gilthead seabream and zebrafish, we report here that the main proinflammatory effects of fish TNF-alpha are mediated through the activation of endothelial cells. Thus, TNF-alpha promotes the expression of E-selectin and different CC and CXC chemokines in endothelial cells, thus explaining the recruitment and activation of phagocytes observed in vivo in both species. We also found that TLR ligands, and to some extent TNF-alpha, were able to increase the expression of MHC class II and CD83 in endothelial cells, which might suggest a role for fish endothelial cells and TNF-alpha in Ag presentation. Lastly, we found that TNF-alpha increases the susceptibility of the zebrafish to viral (spring viremia of carp virus) and bacterial (Streptococcus iniae) infections. Although the powerful actions of fish TNF-alpha on endothelial cells suggest that it might facilitate pathogen dissemination, it was found that TNF-alpha increased antiviral genes and, more importantly, had little effect on the viral load in early infection. In addition, the stimulation of ZF4 cells with TNF-alpha resulted in increased viral replication. Together, these results indicate that fish TNF-alpha displays different sorts of bioactivity to their mammalian counterparts and point to the complexity of the evolution that has taken place in the regulation of innate immunity by cytokines.

Quilty in biopsy is associated with poor prognosis after heart transplantation.

We tested if Quilty (endocardial infiltration of lymphocytes) in routinely processed endomyocardial biopsy is associated with poor outcome after heart transplantation (HTx). Biopsies (n=9829) harvested within the first post-transplant year from 938 patients (778 men, mean age 49 years) were evaluated for Quilty and acute cellular rejection (according to the International Society for Heart and Lung Transplantation, ISHLT, classification). Transplant vasculopathy was evaluated by coronary angiography, and severe stenosis was found in 19% of patients. Survival was tested by Kaplan-Meier and Cox regression analyses for all-cause mortality and major cardiac events (lethal acute cellular rejection, graft loss or myocardial infarction). We found 1840 (19%) Quilty-positive biopsies in 487 Quilty-positive patients (52%). Quilty was more prevalent in women (p=0.038) and younger men (p=0.001), and was correlated with ISHLT grade 1R (OR 1.45, 95% CI 1.36-1.55; p<0.001) and ISHLT grade 2R (OR 2.48, 95% CI 2.21-3.41; p<0.001). Quilty in any biopsy was associated with a higher all-cause mortality (log rank p=0.045) due to a higher risk for major cardiac event (p=0.0001). Multivariate regression analysis showed Quilty (RR 1.69, 95%CI 1.05-2.73) and transplant vasculopathy (RR 2.78, 95%CI 1.68-4.61) as risk factors for major cardiac events and treated hyperlipidemia as lowering the risk for major cardiac events (RR 0.47, 95%CI 0.28-0.77). Quilty is associated with graft loss and poor outcome post HTx. Index biopsy during the first post-transplant year is a useful tool to identify patients at risk and is recommended during routine post-transplant management.

Quilty effect areas are frequently associated with endocardial C4d deposition.

BACKGROUND: The meaning and clinical implications of the Quilty effect (QE) are not entirely clear. In some biopsies we have found complement split C4d deposition in QE areas, but we do fully comprehend the frequency or pathogenic relationships involved. The objective of this study was to gain insight into the immunologic events involved in the QE, and to understand if and how it relates to complement activation. METHODS: Protocol allograft biopsies (January to December 2005) with evidence of the QE, without cellular rejection or changes suspicious for antibody-mediated rejection, were selected for C4d, CD3, CD20 and CD68 immunohistochemistry. RESULTS: Among 128 allograft biopsies (42 patients), 17 (11 patients) fulfilled the inclusion criteria. Eleven of the 17 biopsies (64.7%), from 8 patients, showed C4d deposition in the endocardium; the positivity was interestingly linear in the endocardium and surrounded by the lymphocytes forming the Quilty lesion. In some cases, the linear C4d deposition extended to the endocardium surrounding the QE area. This pattern was not detected in any of 66 heart allograft biopsies without the QE. B cells were second to T cells in their contribution to the QE, comprising a median of 40% (range, 20% to 50%) of the cells. C4d deposition was not associated with clinical alterations. CONCLUSIONS: The QE is frequently associated with C4d deposition in the endocardium of patients without evidence of rejection. This event suggests a pathogenic relationship between the QE and complement activation. It is possible that the simultaneous presence of both features in an allograft heart biopsy, without evidence of rejection, indicates better adaptation of allograft to host ("accommodation"); however, the precise meaning and implications are not yet known.

[Reversible dilated cardiomyopathy in a patient with acute, advanced heart failure and intense endothelial inflammatory reaction in endomyocardial biopsy--a case report]. / Odwracalna kardiomiopatia rozstrzeniowa u chorego z ostra i ciezka niewydolnoscia serca oraz nasilona odpowiedzia zapalna sródblonka w biopsji endomiokardialnej.

Inflammatory response of the endothelium has been increasingly recognized in the aetiopathogenesis of sporadic dilated cardiomyopathy (DCM). It has been shown that up to 2/3 of patients with DCM have immunohistological evidence of enhanced activation of the endothelium. We present a case of a middle-aged patient with a history of hypertension and hyperlipidaemia who developed sudden significant left ventricular dysfunction following flu-like syndrome. Endomyocardial biopsy revealed no myocarditis, but immunohistological features of endothelial activation were present. Additionally, increasing titers of IgG antibodies against PvB19 were observed. During 18 months of standard heart failure treatment along with statin therapy, we observed a significant recovery of left ventricular systolic function, and in this way, reversible dilated cardiomyopathy.

Neutrophil transendothelial migration potential predicts rejection severity in human cardiac transplantation.

OBJECTIVE: Transplant rejection remains a clinical problem despite therapies that focus on lymphocyte suppression, with little attention focused on the neutrophil. Neutrophils are however the first leukocyte to infiltrate the allograft, are capable of causing myocardial damage and may facilitate lymphocytes recruitment. We hypothesised that an early allograft neutrophil infiltration influences rejection severity. METHODS: Myocardial neutrophil infiltration was assessed using CD15 and myeloperoxidase immunohistochemistry of rejection surveillance endomyocardial biopsy specimens from human cardiac transplant recipients (n=18). In patients undergoing cardiac transplantation (n=10), neutrophils were isolated from multiple perioperative blood samples using a ficoll-based density gradient centrifugation method. The expression of the neutrophil adhesion protein CD11b was then assessed using flow cytometry and compared to subsequent endomyocardial biopsy rejection grades. The effects of contemporary immunosuppressive agents on human neutrophil CD11b were also assessed using healthy control volunteers. RESULTS: Myeloperoxidase staining of endomyocardial biopsies from human heart transplant recipients demonstrated a positive correlation between the degree of neutrophil infiltration and rejection severity at the first postoperative biopsy. Rejection severity was unrelated to ischaemic time. Functional assessment of neutrophils obtained from recipients was then performed. Perioperative transplant sampling demonstrated a significant correlation between the preoperative expression of CD11b and rejection grade at the first postoperative biopsy. In addition, dynamic changes in CD11b expression in the first 24 h positively correlated with subsequent rejection severity. In vitro experiments showed that transplant immunosuppression did not alter neutrophil CD11b expression. CONCLUSION: This study demonstrates a potentially greater role for neutrophils in cardiac transplantation than previously recognised, and suggests that blockade of the early allograft neutrophil infiltration might prevent subsequent lymphocyte recruitment and attenuate rejection.