Evidence that humoral allograft rejection in lung transplant patients is not histocompatibility antigen-related

Extracellular vesicles: a potential new player in antibody-mediated rejection in lung allograft recipients

Identification of recipients with pre-existing antibodies and cross-matching of recipient sera with donor lymphocytes have reduced the incidence of antibody-mediated rejection (AMR) after human lung transplantation. However, AMR is still common and requires not only immediate intervention but also has long-term consequences including an increased risk of chronic lung allograft dysfunction (CLAD). The mechanisms resulting in AMR remain largely unknown due to the variation in clinical and histopathological features among lung transplant recipients; however, several reports have demonstrated a strong association between the development of antibodies against mismatched donor human leucocyte antigens [donor-specific antibodies (DSAs)] and AMR. In addition, the development of antibodies against lung self-antigens (K alpha1 tubulin and collagen V) also plays a vital role in AMR pathogenesis, either alone or in combination with DSAs. In the current article, we will review the existing literature regarding the association of DSAs with AMR, along with clinical diagnostic features and current treatment options for AMR. We will also discuss the role of extracellular vesicles (EVs) in the immune-related pathogenesis of AMR, which can lead to CLAD.

The allograft injury marker CXCL9 determines prognosis of anti-HLA antibodies after lung transplantation

Despite the common detection of non-donor specific anti-HLA antibodies (non-DSAs) after lung transplantation, their clinical significance remains unclear. In this retrospective single-center cohort study of 325 lung transplant recipients, we evaluated the association between donor-specific HLA antibodies (DSAs) and non-DSAs with subsequent CLAD development. DSAs were detected in 30% of recipients and were associated with increased CLAD risk, with higher HRs for both de novo and high MFI (>5000) DSAs. Non-DSAs were detected in 56% of recipients, and 85% of DSA positive tests had concurrent non-DSAs. In general, non-DSAs did not increase CLAD risk in multivariable models accounting for DSAs. However, non-DSAs in conjunction with high BAL CXCL9 levels were associated with increased CLAD risk. Multivariable proportional hazards models demonstrate the importance of the HLA antibody-CXCL9 interaction: CLAD risk increases when HLA antibodies (both DSAs and non-DSAs) are detected in conjunction with high CXCL9. Conversely, CLAD risk is not increased when HLA antibodies are detected with low CXCL9. This study supports the potential utility of BAL CXCL9 measurement as a biomarker to risk stratify HLA antibodies for future CLAD. The ability to discriminate between high versus low-risk HLA antibodies may improve management by allowing for guided treatment decisions.

Early Identification of Chronic Lung Allograft Dysfunction: The Need of Biomarkers

A growing number of patients with end-stage lung disease have benefited from lung transplantation (LT). Improvements in organ procurement, surgical techniques and intensive care management have greatly increased short-term graft survival. However, long-term outcomes remain limited, mainly due to the onset of chronic lung allograft dysfunction (CLAD), whose diagnosis is based on permanent loss of lung function after the development of irreversible lung lesions. CLAD is associated with high mortality and morbidity, and its exact physiopathology is still only partially understood. Many researchers and clinicians have searched for CLAD biomarkers to improve diagnosis, to refine the phenotypes associated with differential prognosis and to identify early biological processes that lead to CLAD to enable an early intervention that could modify the inevitable degradation of respiratory function. Donor-specific antibodies are currently the only biomarkers used in routine clinical practice, and their significance for accurately predicting CLAD is still debated. We describe here significant studies that have highlighted potential candidates for reliable and non-invasive biomarkers of CLAD in the fields of imaging and functional monitoring, humoral immunity, cell-mediated immunity, allograft injury, airway remodeling and gene expression. Such biomarkers would improve CLAD prediction and allow differential LT management regarding CLAD risk.

Lung Transplantation

The therapeutic options for patients with advanced pulmonary parenchymal or vascular disorders are currently limited. Lung transplantation remains one of the few viable interventions, but on account of the insufficient donor pool only a minority of these patients actually undergo the procedure each year. Following transplantation there are a number of early and late allograft complications such as primary graft dysfunction, allograft rejection, infection, post-transplant lymphoproliferative disorder and late injury that is now classified as chronic lung allograft dysfunction. The pathologist plays an essential role in the diagnosis and classification of these myriad complications. Although the transplant procedures are performed in selected centers patients typically return to their local centers. When complications arise it is often the responsibility of the local pathologist to evaluate specimens. Therefore familiarity with the pathology of lung transplantation is important.

Antibody-mediated Rejection in Lung Transplantation

There has been increasing awareness of antibody-mediated rejection (AMR) as an important cause of graft failure after lung transplantation in recent years. However, the diagnostic criteria for pulmonary AMR are not well defined. All four tenets of AMR in kidney and heart transplantation, graft dysfunction, complement component deposition, circulating donor-specific antibodies (DSA), and histopathologic changes consistent with AMR, are infrequently present in lung transplantation. Nonetheless, the lung transplant community has made important progress recognizing cases of AMR and developing a definition. However, AMR is often refractory to therapy resulting in graft failure and death. In this review, we discuss the progress and challenges in the diagnosis and therapeutic options for pulmonary AMR. In addition, we briefly examine emerging paradigms of C4d-negative AMR and chronic AMR, and conclude that significant progress is needed to mitigate the effects of humoral immune responses after lung transplantation.

The Presence of Anti-HLA Donor-Specific Antibodies in Lung Allograft Recipients Does Not Correlate With C4d Immunofluorescence in Transbronchial Biopsy Specimens

Context.—C4d immunofluorescence (IF) is a surrogate for development of donor-specific antibodies (DSAs) against human leukocyte antigen (HLA) class I and II antigens in kidney and heart biopsy specimens for monitoring of antibody-mediated (humoral) allograft rejection (AMR). Use of C4d IF in monitoring of lung allografts has shown conflicting results.

Objective.—To determine if C4d IF can be used as a reliable marker for AMR and if it correlates with the presence of DSAs and histologic findings on biopsy.

Design.—All transbronchial biopsies in lung allograft recipients, performed at our institution in a 3-year period, were reviewed. A cohort of 92 patients with 110 corresponding biopsies met the inclusion criteria of (1) having a resulted DSA within 2 weeks of biopsy and (2) having C4d immunofluorescence studies performed and confirmed.

Results.—Twenty-nine patients (31.5%) were positive for DSAs and 63 patients (68.5%) did not develop DSAs. Positive C4d capillary IF was seen in 18 of 110 total biopsy specimens (16.4%). Eight of these biopsy samples were from patients positive for DSAs and 10 were from patients negative for DSAs. The correlation coefficient between the presence of DSAs and C4d IF was 0.1628 (P = .09).

Conclusions.—A significant proportion of DSA-positive patients had negative C4d IF results and frequently have no histologic changes on biopsy specimens. DSA-negative patients can be positive for C4d and may show the same histologic changes as reported for DSA-positive patients. Diagnosis of AMR in lung may require a collaborative approach combining clinical data, DSA status, and histology.

Implications for human leukocyte antigen antibodies after lung transplantation: a 10-year experience in 441 patients

BACKGROUND

Long-term survival after lung transplant is limited by the development of chronic and progressive airflow obstruction, a condition known as bronchiolitis obliterans syndrome (BOS). While prior studies strongly implicate cellular rejection as a strong risk factor for BOS, less is known about the clinical significance of human leukocyte antigen (HLA) antibodies and donor HLA-specific antibodies in long-term outcomes.

METHODS

A single-center cohort of 441 lung transplant recipients, spanning a 10-year period, was prospectively screened for HLA antibodies after transplant using flow cytometry-based methods. The prevalence of and predictors for HLA antibodies were determined. The impact of HLA antibodies on survival after transplant and the development of BOS were determined using Cox models.

RESULTS

Of the 441 recipients, 139 (32%) had detectable antibodies to HLA. Of these 139, 54 (39%) developed antibodies specific to donor HLA. The detection of posttransplant HLA antibodies was associated with BOS (HR, 1.54; P=.04) and death (HR, 1.53; P=.02) in multivariable models. The detection of donor-specific HLA antibodies was associated with death (HR, 2.42; P<.0001). The detection of posttransplant HLA antibodies was associated with pretransplant HLA-antibody detection, platelet transfusions, and the development of BOS and cytomegalovirus pneumonitis.

CONCLUSIONS

Approximately one-third of lung transplant recipients have detectable HLA antibodies, which are associated with a worse prognosis regarding graft function and patient survival.

Interplay between immune responses to HLA and non-HLA self-antigens in allograft rejection

Recent studies strongly suggest an increasing role for immune responses against self-antigens (Ags) which are not encoded by the major histocompatibility complex in the immunopathogenesis of allograft rejection. Although, improved surgical techniques coupled with improved methods to detect and avoid sensitization against donor human leukocyte antigen (HLA) have improved the immediate and short term function of transplanted organs. However, acute and chronic rejection still remains a vexing problem for the long term function of the transplanted organ. Immediately following organ transplantation, several factors both immune and non immune mechanisms lead to the development of local inflammatory milieu which sets the stage for allograft rejection. Traditionally, development of antibodies (Abs) against mismatched donor HLA have been implicated in the development of Ab mediated rejection. However, recent studies from our laboratory and others have demonstrated that development of humoral and cellular immune responses against non-HLA self-Ags may contribute in the pathogenesis of allograft rejection. There are reports demonstrating that immune responses to self-Ags especially Abs to the self-Ags as well as cellular immune responses especially through IL17 has significant pro-fibrotic properties leading to chronic allograft failure. This review summarizes recent studies demonstrating the role for immune responses to self-Ags in allograft immunity leading to rejection as well as present recent evidence suggesting there is interplay between allo- and autoimmunity leading to allograft dysfunction.

SaLUTaRy: survey of lung transplant rejection

BACKGROUND

The International Society for Heart and Lung Transplantation (ISHLT) guidelines on the interpretation of lung rejection in pulmonary allograft biopsy specimens were revised most recently in 2007. The goal of our study was to determine how these revisions, along with nuances in the interpretation and application of the guidelines, affect patient care.

METHODS

A Web-based survey was e-mailed to pathologists and pulmonologists identified as being part of the lung transplant team at institutions in the United States with active lung transplant programs as determined from the Organ Procurement and Transplantation Network Web site (http://optn.transplant.hrsa.gov/members/directory.asp).

RESULTS

Grades B1 and B2 in asymptomatic patients would fall into the same treatment group under the 2007 classification, which combines B1 and B2 into B1R. Also, some pulmonologists would not interpret a pathologic diagnosis of lymphocytic bronchiolitis as grade B rejection, resulting in under-treatment of these patients. Regarding bronchiolitis obliterans, most pulmonologists would treat the patient differently if there were an active mononuclear inflammatory infiltrate, and most pathologists would comment on the presence of such an infiltrate, contrary to the 2007 guidelines, which discourage reporting this infiltrate. We also found discrepancies among pathologists in their interpretation of airway lymphocytic infiltrates, whether eosinophils can be present in bronchial-associated lymphoid tissue, and whether airway inflammation represents rejection or bacterial infection.

CONCLUSIONS

The issue of grading and treating airway inflammation in pulmonary allograft biopsy specimens continues to be problematic, despite revised ISHLT guidelines. Clarification of guidelines for pathologists and pulmonologists using evidence-based criteria could lead to improved communication and patient care.

Complement-mediated microvascular injury leads to chronic rejection

Microvascular loss may be an unappreciated root cause of chronic rejection for all solid organ transplants. As the only solid organ transplant that does not undergo primary systemic arterial revascularization at the time of surgery, lung transplants rely on the establishment of a microcirculation and are especially vulnerable to the effects of microvascular loss. Microangiopathy, with its attendant ischemia, can lead to tissue infarction and airway fibrosis. Maintaining healthy vasculature in lung allografts may be critical for preventing terminal airway fibrosis, also known as the bronchiolitis obliterans syndrome (BOS). BOS is the major obstacle to lung transplant success and affects up to 60% of patients surviving 5 years. The role of complement in causing acute microvascular loss and ischemia during rejection has recently been examined using the mouse orthotopic tracheal transplantation; this is an ideal model for parsing the role of airway vasculature in rejection. Prior to the development of airway fibrosis in rejecting tracheal allografts, C3 deposits on the vascular endothelium just as tissue hypoxia is first detected. With the eventual destruction of vessels, microvascular blood flow to the graft stops altogether for several days. Complement deficiency and complement inhibition lead to markedly improved tissue oxygenation in transplants, diminished airway remodeling, and accelerated vascular repair. CD4+ T cells and antibody-dependent complement activity independently mediate vascular destruction and sustained tissue ischemia during acute rejection. Consequently, interceding against complement-mediated microvascular injury with adjunctive therapy during acute rejection episodes, in addition to standard immunosuppression which targets CD4+ T cells, may help prevent the subsequent development of chronic rejection.

Humoral immunity and the development of obliterative bronchiolitis after lung transplantation: is there a link?

Lung transplantation is considered the definitive treatment for many end-stage lung diseases. However, the lung is rejected more commonly than other solid organ allografts. Obliterative bronchiolitis (OB) is the leading cause of chronic allograft dysfunction, and the key reason why the 5-year survival of lung transplant recipients is only 50%. The pathophysiology of OB is incompletely understood. Although a clear role for the immune response to donor antigens has been observed (also known as anti-human leukocyte antigens), evidence is emerging about the role of autoimmunity to self-antigens. This review highlights the current understanding of humoral immunity in the development of OB after lung transplantation.

Managing complications following lung transplantation

Lung transplantation has become a proven therapeutic option for patients with end-stage lung disease, extending life and providing improved quality of life to those who otherwise would continue to be breathless and oxygen-dependent. Over the past 20 years, considerable experience has been gained in understanding the multitude of medical and surgical issues that impact upon patient survival. Today, clinicians have an armamentarium of tools to manage diverse problems such as primary graft dysfunction, acute and chronic allograft rejection, airway anastomotic issues, infectious complications, renal dysfunction, diabetes and osteoporosis, hematological and gastrointestinal problems, malignancy, and other unique issues that confront immunosuppressed solid organ transplant recipients.

The histopathology of lung allograft dysfunction associated with the development of donor-specific HLA alloantibodies

The histopathology of antibody-mediated rejection in lung allografts, outside of classical hyperacute rejection, has been poorly defined, in part because of the difficulty in identifying potential alloantibodies and in separating alloreactive and nonspecific complement-mediated reactions. In this study, we looked at lung biopsies coinciding with the development of anti-human leukocyte antigen (anti-HLA) antibodies and lung dysfunction in a diverse group of lung transplant recipients over a 3-year period. We identified 23 patients and found that 17 had coexistent high-grade acute cellular rejection, 5 had patchy acute lung injury, and 1 had bronchiolitis at the time that anti-HLA alloantibodies appeared. Capillaritis was seen in 4/22 (18%) cases, usually in the context of cellular rejection. When the 17 cases of acute cellular rejection with coexistent anti-HLA antibodies were compared with a matched group of 26 patients with equivalent cellular rejection grade without anti-HLA antibodies, the only morphologic feature that separated the 2 groups was capillaritis seen in a minority of cases. C4d deposits were seen in both groups, although more frequently in those cases with anti-HLA antibodies (76% vs. 24%). The development of anti-HLA alloantibodies often occurs in the setting of acute cellular rejection, which in only a minority of cases can be identified as likely having an antibody-mediated component. C4d staining does not consistently separate the 2 groups. Identifying and ascribing allograft dysfunction to antibody-mediated rejection related to the development of anti-HLA antibodies is a difficult task that cannot be solved exclusively by morphology and requires significant clinicopathologic correlation.

Plasma Exchange and Immunoadsorption of Patients with Thoracic Organ Transplantation

Primary organ failure after transplantation (TX) remains a serious complication and leads to a high percentage of lethality. It is known, however, that the speed of rejection and tissue destruction depends on 3 main factors: antibody titer, the ability of the tissue to repair itself, and immunosuppressive measures. Especially with evidence for antibodies against human leukocyte antigen (HLA-ab), the immunological risk of persistent and acute episodes of rejection increases. The role of non-HLA-ab in rejection episodes is often underestimated and should be studied further. Antibody-mediated rejection (AMR) is still an unsolved problem in thoracic organ TX. An essential pillar of antihumoral therapy are the extracorporeal procedures like plasmapheresis (PP), therapeutic plasma exchange (TPE), and immunoadsorption (IA), because only they have the ability to remove preformed or de novo developed antibodies quickly and effectively. The quick removal of antibodies and other plasma factors through TPE or IA remains an effective and supportive method for treating AMR and allows the TX despite preformed antibodies. The pertinent literature does not disclose, however, how often and for how long treatment should be administered. It is known, that repeated treatment cycles with adequately processed plasma volume must be used to overcome redistribution of pathological antibodies. Based on our experience in heart transplant recipients with compromised graft function due to non-HLA-ab and HLA-ab, IA seems to be more effective.

Autoantibody formation in human and rat studies of chronic rejection and primary graft dysfunction

Lung transplantation is considered a definitive treatment for many lung diseases. However, rejection and other pathologic entities are major causes of morbidity and mortality for lung transplant recipients. Primary graft dysfunction (PGD) and obliterative bronchiolitis (OB) are the leading causes of early and late mortality, respectively. While the immune basis of PGD has not been clearly defined, evidence is emerging about roles for autoantibodies in this process. Similarly, the pathogenesis of OB has been linked recently to autoimmunity. This review will highlight the current understanding of autoantibodies in PGD and OB post lung transplantation.

Modifiers of complement activation for prevention of antibody-mediated injury to allografts

PURPOSE OF REVIEW

Improvements in prevention and management of cellular rejection of solid organ transplants, coupled with increasing numbers of sensitized patients, have focused attention on antibody-mediated rejection (AbMR). Complement is a critical component of AbMR, in addition to interfacing between innate and adaptive immunity and the coagulation cascade. This article reviews complement biology and strategies to overcome complement in AbMR, cognisant that antibody can act independently of complement.

RECENT FINDINGS

The past decade has witnessed an improvement in the prevention and treatment of AbMR as a result of solid-phase assays to determine antibody specificity, definition of histopathological criteria, and use of plasmapheresis and/or intravenous immunoglobulin (IVIG). Nonetheless, AbMR continues to impact adversely on short- and long-term graft survival. Use of B and/or T-lymphocyte-depleting therapies has not shown measurable benefit, and the need remains for therapies that deplete antibody, or provide better protection from complement-mediated damage. Disordered complement activity in human diseases such as paroxysmal nocturnal haemoglobinuria, has provided additional impetus to pursuing therapeutic complement inhibition. Preliminary data from C5 inhibition with eculizumab in the treatment and prevention of AbMR have shown promise. Trials with recombinant human inhibitors of C1 (effective in angioedema) to prevent or treat AbMR are beginning.

SUMMARY

Despite current limitations, 'protection' of the transplant through plasmapheresis and/or IVIG enables many allografts to survive in sensitized recipients. Elucidating the pathways mediating graft acceptance, by constitutive antibody deletion, or 'accommodation' (wherein donor organ remains uninjured despite antibody binding), or other local protective mechanism(s), is an equally important challenge in the quest to overcome AbMR.

Ultrastructure as a Diagnostic Adjunct in the Evaluation of Lung Allograft Biopsies

Humoral immunity contributes significantly to lung graft dysfunction. Recognizing a role of ultrastructural studies in the evaluation and diagnosis of chronic humoral allograft rejection in the kidney, the authors sought to explore its utility as a diagnostic adjunct in lung allograft biopsies. Ultrastructural studies were conducted on 44 biopsies from 26 lung transplant recipients. Endothelial cell activation and necrosis were seen in the setting of acute humoral allograft rejection. Septal chronic vasculopathic changes of thickening and lamellation of the basement membrane zone (BMZ) and BMZ collagen deposition were correlated with greater numbers of humoral allograft rejection episodes and with the development of chronic graft dysfunction/bronchiolitis obliterans syndrome. There was a positive correlation between the extent of septal fibrosis and certain chronic vasculopathic changes, namely collagen deposition in the BMZ and BMZ wrinkling. Patients with chronic graft dysfunction and multiple rejection episodes manifested low diffusion capacities (less than 50% predicted). The results indicate that ultrastructural analysis is useful in identification of septal fibrosis and chronic vasculopathy of the septal microvasculature, correlating with chronic graft dysfunction, encompassing not only fibrotic sequelae of the bronchial wall but also irreversible terminal lung parenchymal changes, the latter associated with repeated episodes of humoral rejection.

Mechanisms of complement activation, C4d deposition, and their contribution to the pathogenesis of antibody-mediated rejection

Complement split products have emerged as useful markers of antibody-mediated rejection in solid organ transplants. One split product, C4d, is now widely accepted as a marker for antibody-mediated rejection in renal and cardiac allografts. This review summarizes the rationale for the use of C4d as a marker of antibody-mediated rejection, along with the clinical evidence supporting its use in the clinical diagnosis of antibody-mediated rejection. Antibody-independent mechanisms by which C4d can be activated by the classical and lectin pathways of complement activation are also identified. Finally, mechanisms by which complement activation stimulates effector cells (neutrophils, monocytes, macrophages, platelets, and B and T lymphocytes) as well as target cells (endothelial cells) are discussed in relation to antibody-mediated allograft rejection.

Acute rejection and humoral sensitization in lung transplant recipients

Despite the recent introduction of many improved immunosuppressive agents for use in transplantation, acute rejection affects up to 55% of lung transplant recipients within the first year after transplant. Acute lung allograft rejection is defined as perivascular or peribronchiolar mononuclear inflammation. Although histopathologic signs of rejection often resolve with treatment, the frequency and severity of acute rejections represent the most important risk factor for the subsequent development of bronchiolitis obliterans syndrome (BOS), a condition of progressive airflow obstruction that limits survival to only 50% at 5 years after lung transplantation. Recent evidence demonstrates that peribronchiolar mononuclear inflammation (also known as lymphocytic bronchiolitis) or even a single episode of minimal perivascular inflammation significantly increase the risk for BOS. We comprehensively review the clinical presentation, diagnosis, histopathologic features, and mechanisms of acute cellular lung rejection. In addition, we consider emerging evidence that humoral rejection occurs in lung transplantation, characterized by local complement activation or the presence of antibody to donor human leukocyte antigens (HLA). We discuss in detail methods for HLA antibody detection as well as the clinical relevance, the mechanisms, and the pathologic hallmarks of humoral injury. Treatment options for cellular rejection include high-dose methylprednisolone, antithymocyte globulin, or alemtuzumab. Treatment options for humoral rejection include intravenous immunoglobulin, plasmapheresis, or rituximab. A greater mechanistic understanding of cellular and humoral forms of rejection and their role in the pathogenesis of BOS is critical in developing therapies that extend long-term survival after lung transplantation.

Pulmonary capillaritis as a manifestation of acute humoral allograft rejection following infant lung transplantation

Pulmonary capillaritis has been described in adult lung transplant recipients, but has not been previously reported in pediatric recipients. We report a case of posttransplant pulmonary capillaritis in an 8-month-old infant, and demonstrate evidence of C4d deposition and B-lymphocytes in the allograft, donor anti-HLA antibodies in the serum and a clinical and immunohistochemical response to anti-CD20 monoclonal antibody (rituximab) therapy. These findings strongly support the hypothesis that pulmonary capillaritis may represent a form of acute humoral rejection in the lung allograft that is less common than, and clinically and histologically distinct from, typical acute cellular rejection.

Humoral responses directed against non-human leukocyte antigens in solid-organ transplantation

Antibody-mediated mechanisms have a major impact on allograft function and survival. During the last decade, improved immunohistochemical and serologic diagnostic procedures have been developed to monitor antibody responses against human leukocyte antigens (HLA). Acute and chronic allograft rejection can occur in HLA-identical sibling transplants implicating the importance of immune response against non-HLA targets. Non-HLA, complement and noncomplement-fixing antibodies may be responsible for a variety of allograft injuries, reflecting the complexity of their acute and chronic actions. Non-HLA antibodies may occur as alloantibodies or autoantibodies. Their antigenic targets described, thus, far include various minor histocompatibility antigens, vascular receptors, adhesion molecules, and intermediate filaments. An analysis of the subtle mechanistic differences in the individual antibody responses directed against non-HLA may help to identify patients at particular risk for irreversible acute or chronic allograft injuries and improve overall outcomes. This review summarizes the current state of research, development in diagnostic and therapeutic strategies, discusses some emerging problems, and provides perspectives in the area of humoral response against non-HLA in solid-organ transplantation.

Anti-type V collagen humoral immunity in lung transplant primary graft dysfunction

Primary graft dysfunction (PGD) is a major complication following lung transplantation. We reported that anti-type V collagen (col(V)) T cell immunity was strongly associated with PGD. However, the role of preformed anti-col(V) Abs and their potential target in PGD are unknown. Col(V) immune serum, purified IgG or B cells from col(V) immune rats were transferred to WKY rat lung isograft recipients followed by assessments of lung pathology, cytokines, and PaO(2)/FiO(2), an index of lung dysfunction in PGD. Immune serum, purified IgG, and B cells all induced pathology consistent with PGD within 4 days posttransfer; up-regulated IFN-gamma, TNF-alpha, and IL-1beta locally; and induced significant reductions in PaO(2)/FiO(2). Depleting anti-col(V) Abs before transfer demonstrated that IgG2c was a major subtype mediating injury. Confocal microscopy revealed strong apical col(V) expression on lung epithelial, but not endothelial cells; which was consistent with the ability of col(V) immune serum to induce complement-dependent cytotoxicity only in the epithelial cells. Examination of plasma from patients with or without PGD revealed that higher levels of preformed anti-col(V) Abs were strongly associated with PGD development. This study demonstrates a major role for anti-col(V) humoral immunity in PGD, and identifies the airway epithelium as a target in PGD.

C4d deposition and cellular infiltrates as markers of acute rejection in rat models of orthotopic lung transplantation

BACKGROUND

C4d is a useful marker of antibody-mediated rejection in cardiac and renal transplants, but clinical studies examining correlations between circulating alloantibodies, C4d deposition, and rejection in lung transplants have yielded conflicting results.

METHODS

We studied circulating alloantibody levels and C4d deposition in two rat models of lung transplantation: Brown Norway (BN) to Wistar-Kyoto (WKY) and PVG.R8 to PVG.1U lung allografts. The availability of C6 deficient (C6-) and C6 sufficient (C6+) PVG 1U rats allowed evaluation of the effects of the terminal complement components on graft injury and C4d deposition.

RESULTS

The lung allografts had histologic features resembling human posttransplant capillaritis, characterized by neutrophilic infiltration of alveoli, edema, and hemorrhage. Immunoperoxidase stains on cross sections of allografts showed intense, diffuse, C4d deposition in a continuous linear pattern on the vascular endothelium. C4d deposits were found in both BN to WKY and PVG R8 to 1U allografts, whereas no staining was detectable in WKY to WKY isografts or native lungs. Complement deposition was associated with vascular disruption in C6+, but not in C6- recipients. The presence of circulating donor-specific alloantibodies was verified by flow cytometry. Cell-specific staining revealed perivascular accumulation of macrophages and T lymphocytes whereas neutrophils were sequestered in the intravascular and alveolar capillary compartments.

CONCLUSIONS

The deposition of C4d on vascular endothelium as well as the coincident presence of alloantibodies is consistent with previous findings in antibody-mediated rejection of renal and cardiac transplants. Furthermore, the histological features of our allografts support the concept that posttransplant capillaritis is a form of humoral rejection.

An immunohistochemical evaluation of C4d deposition in pediatric inflammatory liver diseases

C4d is a marker of the activated complement cascade used to assess the humoral component of rejection, mostly in kidney allograft transplants. The role of C4d deposition has recently been addressed in hepatic allograft but has never been tested in a series of inflammatory liver diseases without previous liver transplantation. The aim of this study was to compare the immunohistochemistry profile of C4d deposition in a pediatric population, between a cohort of patients with autoimmune hepatitis (AIH) and a series of patients with chronic viral hepatitis B or C. Immunohistochemical analysis was performed on 64 liver biopsies. C4d deposition was observed in 25 (83%) of 30 AIH biopsies examined, in 6 (40%) of 15 hepatitis C biopsies, and in 17 (89%) of 19 hepatitis B biopsies. No expression of C4d was observed in 4 noninflammatory liver specimens used as negative controls. In the AIH group, a staining of the periportal sinusoids was often observed, as well as focal periductal reinforcement. Centrolobular vein staining was observed in the 3 hepatitis groups with a higher frequency in viral hepatitis B biopsies. Regardless of the etiology, lymphoid aggregates demonstrated an accentuation of the staining. These results confirm a role for a humoral immune response in pediatric autoimmune as well as in viral hepatitis. The relative ratios of positive cases imply that this immunostaining does not represent a strong diagnostic criterion in the differentiation between viral hepatitis and AIH. However, differences in the pattern of the staining were observed, depending on the etiology of the disease. The high prevalence of C4d reactivity in viral hepatitis strongly suggests that C4d does not represent a useful marker in the differentiation between acute rejection and viral hepatitis relapse in liver transplants.

Th-17, monokines, collagen type V, and primary graft dysfunction in lung transplantation

RATIONALE

The pathogenesis of primary graft dysfunction (PGD), a serious complication of lung transplantation, is poorly understood. Human studies and rodent models have shown that collagen type V (col[V]), stimulates IL-17-dependent cellular immunity after lung transplantation.

OBJECTIVES

To determine whether patients with end-stage lung disease develop pretransplant col(V)-specific cellular immunity, and if so, the impact of this response on PGD.

METHODS

Trans-vivo delayed-type hypersensitivity (TV-DTH) assays were used to evaluate memory T-cell responses to col(V) in 55 patients awaiting lung transplantation. Pa(O(2))/Fi(O(2)) index data were used to assess PGD. Univariate risk factor analysis was performed to identify variables associated with PGD. Rats immunized with col(V) or irrelevant antigen underwent lung isografting to determine if prior anti-col(V) immunity triggers PGD in the absence of alloreactivity.

MEASUREMENTS AND MAIN RESULTS

We found that 58.8% (10/17) of patients with idiopathic pulmonary fibrosis, and 15.8% (6/38) of patients without idiopathic pulmonary fibrosis tested while on the wait list for a lung transplant were col(V) DTH positive. Col(V) reactivity was CD4(+) T-cell and monocyte mediated, and dependent on IL-17, IL-1beta, and tumor necrosis factor (TNF)-alpha. Pa(O(2))/Fi(O(2)) indices were impaired significantly 6-72 hours after transplantation in col(V)-reactive versus nonreactive patients. Univariate risk factor analysis identified only preoperative TV-DTH to col(V) and ischemic time as predictors of PGD. Finally, in a rat lung isograft model, col(V) sensitization resulted in significantly lower Pa(O(2))/Fi(O(2)), increased local TNF-alpha and IL-1beta production, and a moderate-to-severe bronchiolitis/vasculitis when compared with control isografts.

CONCLUSIONS

The data suggest that activation of innate immunity by col(V)-specific Th-17 memory cells represents a novel pathway to PGD after lung transplantation.

Pathology of lung transplantation

The International Society for Heart and Lung Transplantation has a standardized nomenclature for the evaluation of lung allografts. Rejection of the lung allograft is divided into acute and chronic forms. Acute cellular rejection is characterized by perivascular accumulations of mononuclear cells and eosinophils; bronchiolar inflammation is also included in the grading scheme. Acute antibody-mediated rejection in lung allografts is not well defined. Chronic rejection is manifest by fibrous scarring narrowing the lumen of bronchioles, arteries, and veins. The diagnosis of rejection requires the exclusion of infection and other pathology in the allograft.

Lung Transplantation: Current Status and Challenges

The lung is an anatomically complex vital organ whose normal physiology depends on actively regulated ventilation and perfusion, and maintenance of a delicate blood-air barrier over a huge surface area in direct contact with a potentially hostile environment. Despite significant progress over the past 25 years, both short- and long-term outcomes remain significantly inferior for lung recipients relative to other "solid" organs. This review summarizes the current status of lung transplantation so as to frame the principle challenges currently facing end-stage lung-failure patients and the practitioners who care for them.

C3d and the Septal Microvasculature as a Predictor of Chronic Lung Allograft Dysfunction

Studies have shown a potential role for humoral rejection in the evolution of lung graft dysfunction, apparently based on antibodies without human leukocyte antigen specificity. The correlation between extent of C4d deposition with clinical status further illustrates the importance of humoral immunity. Our study examines the potential value of C3d as a further diagnostic adjunct. C3d deposition was examined in lung allograft specimens using frozen tissue indirect direct immunofluorescence (IIF) and avidin biotin immunohistochemical applied to paraffin embedded tissue. Intermediate/extensive amounts of C3d using IIF and immunohistochemical (IH) methodologies correlated with chronic graft dysfunction; IIF C3d deposition was associated with septal and bronchial wall fibrosis (p < 0.0001). Weak/absent amounts of IIF and IH C3d correlated with clinical stability (p < 0.0001). Higher levels of C3d by IH were more sensitive than by IIF as a bronchiolitis obliterans syndrome determinant. C3d and C4d deposition using immunofluorescence and IH were correlated (p < 0.00001). C3d deposition appears prognostically significant. Higher tissue expression of C3d mark chronic graft dysfunction/persistent graft failure following transplantation. The close correlation between C3d and C4d lends credence to the role of humoral allograft rejection as a pulmonary graft dysfunction contributing factor. C3d by IH manifests higher sensitivity but similar specificity compared to C3d by IIF.

Role of Flow Cytometry to Define Unacceptable HLA Antigens in Lung Transplant Recipients with HLA-Specific Antibodies

BACKGROUND

Antidonor HLA-specific antibodies have been associated with hyperacute rejection and primary graft failure in lung transplant recipients. Thus, transplant candidates with HLA-specific antibodies generally undergo prospective crossmatching to exclude donors with unacceptable HLA antigens. However, the need to perform a prospective crossmatch limits the donor pool and is associated with increased waiting list times and mortality. A virtual crossmatch strategy using flow cytometry, which enables precise determination of HLA-specific antibody specificity, was compared to prospective crossmatching in sensitized lung transplant candidates.

METHODS

In all, 341 lung transplant recipients were analyzed retrospectively (April 1992 to July 2003). Sixteen patients with HLA-specific antibodies underwent transplantation based on flow cytometric determination of antibody specificity and 10 underwent prospective crossmatching.

RESULTS

Freedom from bronchiolitis obliterans syndrome (BOS) at three years was similar in those undergoing a virtual crossmatch, those undergoing prospective crossmatching, and those without HLA-specific antibodies (80.4% +/- 13.4, 85.7% +/- 13.2, and 73.8% +/- 2.8, respectively, P = 0.88). Three-year survival was also comparable (87.5% +/- 8.3, 70.0% +/- 14.5, and 78.5% +/- 2.4, respectively, P = 0.31). Elimination of prospective crossmatching for sensitized patients was associated with a significant decrease in time on the waiting list (P < 0.01) and in waiting list mortality (P < 0.05). All 16 patients undergoing a virtual crossmatch had negative retrospective crossmatches.

CONCLUSIONS

By carefully determining the specificity of HLA-specific antibodies, flow cytometry methodologies enable the prediction of negative crossmatch results with up to 100% accuracy, enabling the determination of appropriateness of donors. Using this virtual crossmatch strategy, crossmatching can be safely omitted prior to lung transplantation, thereby decreasing waiting list time and mortality rates for candidates with HLA-specific antibodies.

Pulmonary Capillaritis in Lung Transplant Recipients: Treatment and Effect on Allograft Function

The clinical outcomes of lung transplant recipients presenting with post-transplant pulmonary capillaritis have not been well described. We retrospectively reviewed 40 cases of biopsy-proven pulmonary capillaritis in lung transplant recipients. Patients presented with a clinical syndrome characterized by dyspnea, hypoxemia, abnormal chest X-ray, and a decrease in forced expiratory volume in 1 second (FEV1); 25% presented with hemoptysis, and 18% with fulminant respiratory failure. Therapy with intravenous corticosteroids resulted in clinical improvement in 17 cases (43%). A response to plasmapheresis was seen in 12 (67%) of 18 cases refractory to corticosteroids. There were 5 deaths within 3 months of diagnosis. Nine (82%) of 11 lung transplant recipients who presented with capillaritis within 4 weeks post-transplant were alive at 1 year; all but 1 patient achieved expected percent predicted FEV1 values. Only 3 (14%) of 21 who presented with capillaritis > 1 month after transplant had a >20% decrease in the FEV1 after 12 months. These results suggest that post-transplant pulmonary capillaritis is (1) likely a form of acute allograft rejection clinically and histologically distinct from typical acute rejection, (2) less responsive to corticosteroid therapy than typical acute rejection, and (3) not associated with long-term adverse effects on allograft function.

Humoral rejection of organ allografts

In recent years, the deleterious clinical consequences of recipient de novo alloantibody production against HLA antigens from human organ allografts have been extensively investigated. In kidney transplantation, the identification of the complement C4d fragment in peritubular capillaries as a specific marker for humoral rejection has helped to define and characterize distinct clinical alloantibody-mediated syndromes. This knowledge is relevant for patient management as new therapeutic strategies to remove and control anti-donor antibody production, particularly in the setting of acute humoral rejection, have been reported. For recipients of nonrenal organ allografts such as heart transplant recipients, de novo anti-HLA alloantibody may also be important, although more studies are needed before clear guidelines can be proposed.

C4d Staining of Pulmonary Allograft Biopsies: An Immunoperoxidase Study

BACKGROUND

The role of antibody-mediated/humoral rejection in lung allografts is not fully elucidated. In other organ systems, deposition of a specific complement product, C4d, is a sensitive and specific marker for humoral rejection. C4d can be evaluated in tissue biopsies by immunofluorescence or light microscopic immunohistochemical staining techniques. Using immunohistochemical staining techniques we sought to determine whether there was any specific staining pattern for C4d in lung allograft biopsies with or without the diagnosis of acute or chronic cellular or humoral rejection.

METHODS

A total of 68 lung transplant biopsies, performed at UCLA Medical Center from January 2002 to August 2004, were collected and the paraffin blocks were re-cut and stained for C4d by an immunoperoxidase technique. The cases were separated by the presence or absence of features of acute and/or chronic rejection based on the International Society for Heart and Lung Transplantation working formulation for the classification of pulmonary allograft rejection, revised 1995. The pattern of staining for C4d was then systematically examined.

RESULTS

Positive staining in a variable, focal non-specific pattern was observed. There was no consistent staining pattern within the different diagnostic groups.

CONCLUSIONS

C4d staining of paraffin-embedded lung allograft biopsies, using currently available techniques, does not identify acute or chronic cellular or humoral rejection in lung allograft tissue.

C4d deposition in lung allografts is associated with circulating anti-HLA alloantibody

The complement activation demonstrated by vascular C4d deposition is used to diagnose antibody-mediated rejection (AMR) in renal allografts, but remains controversial in lung transplantation (LTX).

METHODS

C4d deposition was assessed by immunohistochemistry in 192 lung transplant biopsies from 32 patients. ELISA analysis was performed on 415 serum samples in those 32 temporally and rejection-grade matched LTX patients; 16 patients developed HLA-Ab, while the other 16 patients remained negative. The specificity of C4d staining was further compared in 18 additional LTX patients without HLA-Ab or acute cellular rejection (ACR), but in the presence of CMV-pneumonitis or reperfusion injury.

RESULTS

Specific subendothelial C4d deposition was seen in 5 of 16 (31%) patients with HLA-Ab and was absent in 16 patients without HLA-Ab (p<0.05). All patients with specific C4d deposition exhibited donor-specific HLA-Ab. There were 13 patients with bronchiolitis obliterans syndrome in the group of 16 HLA-Ab positive patients, versus 2/16 in ELISA-negative patients (p<0.005). One of 7 patients with CMV pneumonitis and 2 of 11 patients with reperfusion injury also showed C4d positivity (not statistically significant).

CONCLUSIONS

In this study, specific subendothelial C4d deposition was a marker for the involvement of HLA-Ab in lung allograft rejection. The patchy nature, low sensitivity, and specificity of C4d staining might limit clinical use in protocol biopsies. However, in patients with decreasing pulmonary function, refractory ACR and/or HLA-Ab, specific C4d deposition may serve as a marker of coexistent AMR.

Biliary epithelial cell antibodies induce expression of toll-like receptors 2 and 3: a mechanism for post-liver transplantation cholangitis?

Studies to determine the role of preformed antibodies to biliary epithelial cells (BECs) in liver transplant rejections have been initiated. However, the clinical importance of these antibodies in the posttransplantation period still remains to be elucidated. Reactivity to BECs isolated from a normal healthy liver was investigated in sera of 56 patients before and after liver transplantation (LTX) using flow cytometry. Functional capacity of BEC antibodies was determined by the ability to induce expression of Toll-like receptors (TLRs) on BECs. Cytokine and chemokine production induced by BEC antibodies was determined by enzyme-linked immunosorbent assay. In all, 7 patients (13%) had BEC antibodies only pre-LTX, 14 (25%) only after LTX, 18 (32%) both before and after LTX, and 17 (30%) had no detectable antibodies. Presence of preformed BEC antibodies correlated with acute rejections (P < 0.03). Deposition of immunoglobulins in bile ducts was detected in biopsies of patients during rejections. Significantly higher numbers of patients with post-LTX antibodies (9 of 32) developed cholangitis, compared with 0 of 17 without antibodies (P < 0.02). Specificity studies indicated that these antibodies were both non-HLA- and HLA-specific. Normal BECs expressed mRNA but not the proteins for the TLRs. However, treatment with F(ab')2 fragments of BEC antibodies induced protein expression of TLRs 2 and 3 and significantly high production of interleukin (IL)-6, monocyte chemoattractant protein (MCP)-1, macrophage inflammatory protein (MIP)-1alpha, epithelial neutrophil activating peptide (ENA)-78, and IL-8. In conclusion, BEC antibodies via induction of TLR2 and TLR3 expression, as well as inflammatory cytokine and chemokine production may induce epithelial cell inflammatory responses to bacterial components and contribute to posttransplantation cholangitis.