The bone marrow functions as the central site of proliferation for long-lived NK cells.

NK cells play an important role in the early defense against invading pathogens. Although it is well established that infection leads to a substantial, local increase in NK cell numbers, little is known about the mechanisms that trigger their proliferation and migration. In this study, we investigated the dynamics of NK cell responses after intranasal respiratory virus infection. We show that NK cell numbers increased in the airways after influenza virus infection but find no evidence of proliferation either at the site of infection or in the draining lymph nodes. Instead, we find that the bone marrow (BM) is the primary site of proliferation of both immature and mature NK cells during infection. Using an adoptive transfer model, we demonstrate that peripheral, long-lived and phenotypically mature NK cells migrate back to the BM and proliferate there, both homeostatically and in response to infection. Thus, the BM is not only a site of NK cell development but also an important site for proliferation of long-lived mature NK cells.

Association of large-airway lymphocytic bronchitis with bronchiolitis obliterans syndrome.

RATIONALE: Lung transplantation offers great promise for otherwise terminal lung diseases, but the development of bronchiolitis obliterans syndrome (BOS) continues to limit survival. Although acute rejection and lymphocytic bronchiolitis have been identified as risk factors for the development of BOS, it is unclear whether large-airway lymphocytic inflammation conveys the same risk. OBJECTIVES: We evaluated lymphocytic bronchitis on endobronchial biopsies as a risk factor for BOS and mortality. METHODS: Endobronchial biopsies were collected and graded during surveillance after lung transplantation. We assessed samples with negative cultures collected in the first 90 days from 298 subjects and compared large-airway lymphocytic bronchitis assessed by a 0-2 "E-score" and with standard A and BR pathology scores for acute rejection and small-airway lymphocytic bronchiolitis, respectively. MEASUREMENTS AND MAIN RESULTS: We found surprisingly little association between large- and small-airway lymphocytic inflammation scores from a given bronchoscopy. Endobronchial lymphocytic bronchitis was more prevalent in subjects in BOS stage 0p and BOS stages 1-3 at the time of biopsy. Within 90 days after transplantation, increasing maximum E-score was associated with greater risk of BOS (adjusted hazard ratio, 1.76; 95% confidence interval, 1.11-2.78; P = 0.02) and in this analysis 90-day maximum E-scores were the only score type predictive of BOS (P < 0.01). CONCLUSIONS: These results support a multicenter study to evaluate endoscopic biopsies for the identification of patients at increased risk for BOS. The association of endobronchial lymphocytic inflammation and BOS may have mechanistic implications.

Isolation of fibroblasts and epithelial cells in bronchoalveolar lavage (BAL).

The long-term outcome of lung transplants is poor with 60%-70% of patients developing chronic rejection. Chronic rejection is manifested histologically by obliterative bronchiolitis with bronchiolitis obliterans syndrome (BOS), the clinical surrogate. Recent studies suggest that fibroblasts and epithelial cells present in bronchoalveolar lavage (BAL) may be a clinically relevant biomarker for BOS. The goal of this investigation was to develop a fast, repeatable method to individually isolate these low-frequency cell types. Fibroblasts and epithelial cells were isolated from BAL using attachment methods and the phenotype of the cells confirmed using immunostaining for vimentin (fibroblasts) and epithelial cell adhesion molecule (EpCAM, epithelial cells). Both fibroblasts and epithelial cells were isolated in every sample of BAL processed with the frequency of fibroblasts ranging from 0.03% to 0.48% and epithelial cells ranging from 0.05% to 1.5% of the total sample. Additional studies were performed using cytospins of cells after macrophages were depleted; cells exhibiting characteristics of both fibroblasts and epithelial cells were observed. The frequency of the cells of interest suggests that conventional methods of immunomagnetic isolation will not be effective in isolating these subpopulations. Finally, some of the low-frequency cells isolated via cytospin exhibit characteristics of epithelial to mesenchymal transition (which was not observed in plating incubations), indicating that the epithelial to mesenchymal cell transition fibroblasts may be nonadherent. In future studies, this technique and dataset may be of use to statistically correlate low-frequency cell type abundance to the onset and development of BOS.

[Predictors of osteopenic syndrome in idiopathic pulmonary fibrosis].

AIM: To evaluate the functional state of bone tissue in patients with idiopathic pulmonary fibrosis (IPF), waiting for lung transplantation, and to determine possible predictors of lower bone mineral density (BMD) in this pathology in the pretransplantation period. SUBJECTS AND METHODS: Forty-nine IPF patients waiting for lung transplantation were examined. The patients' mean age was 53.4 +/- 6.4 years. BMD in the lumbar spine (L(II)-L(IV)) and femoral neck (FN) was estimated using dual-energy X-ray absorptiometry. All the patients underwent external respiratory function test, pulmonary diffusing capacity (DL(CO)), gasometry, and 6-minute walk test (6'WT). RESULTS: Osteopenia was recorded in 77% of the examinees, of them 28% had osteoporosis (OP). Normal BMD in both L(II)-L(IV) and FN was found only in 13% of the patients. The T score in L(II)-L(IV) was directly related to body mass index. There was a direct correlation between BMD in L(II)-L(IV) and FN, forced vital capacity (FVC), DL(CO), and arterial blood oxygen saturation (SaO2) and an inverse correlation with arterial carbon dioxide partial pressure (pCO2). No significant correlation was found between the distance covered in 6'WT, FEV1, pO2, and BMD in both L(II)-L(IV) and FN. Six (15%) subjects had atraumatic fractures at different sites. CONCLUSION: Osteopenia is a common systemic manifestation in patients with IPF in the pre-transplantation period. BMI, FVC, exercise desaturation, and DL(CO) may be considered as predictors for the development of OP initiated by IPF.

Donor lung derived myeloid and plasmacytoid dendritic cells differentially regulate T cell proliferation and cytokine production.

BACKGROUND: Direct allorecognition, i.e., donor lung-derived dendritic cells (DCs) stimulating recipient-derived T lymphocytes, is believed to be the key mechanism of lung allograft rejection. Myeloid (cDCs) and plasmacytoid (pDCs) are believed to have differential effects on T cell activation. However, the roles of each DC type on T cell activation and rejection pathology post lung transplantation are unknown. METHODS: Using transgenic mice and antibody depletion techniques, either or both cell types were depleted in lungs of donor BALB/c mice (H-2(d)) prior to transplanting into C57BL/6 mice (H-2(b)), followed by an assessment of rejection pathology, and pDC or cDC-induced proliferation and cytokine production in C57BL/6-derived mediastinal lymph node T cells (CD3+). RESULTS: Depleting either DC type had modest effect on rejection pathology and T cell proliferation. In contrast, T cells from mice that received grafts depleted of both DCs did not proliferate and this was associated with significantly reduced acute rejection scores compared to all other groups. cDCs were potent inducers of IFNγ, whereas both cDCs and pDCs induced IL-10. Both cell types had variable effects on IL-17A production. CONCLUSION: Collectively, the data show that direct allorecognition by donor lung pDCs and cDCs have differential effects on T cell proliferation and cytokine production. Depletion of both donor lung cDC and pDC could prevent the severity of acute rejection episodes.

Leaky lysosomes in lung transplant macrophages: azithromycin prevents oxidative damage.

BACKGROUND: Lung allografts contain large amounts of iron (Fe), which inside lung macrophages may promote oxidative lysosomal membrane permeabilization (LMP), cell death and inflammation. The macrolide antibiotic azithromycin (AZM) accumulates 1000-fold inside the acidic lysosomes and may interfere with the lysosomal pool of Fe. OBJECTIVE: Oxidative lysosomal leakage was assessed in lung macrophages from lung transplant recipients without or with AZM treatment and from healthy subjects. The efficiency of AZM to protect lysosomes and cells against oxidants was further assessed employing murine J774 macrophages. METHODS: Macrophages harvested from 8 transplant recipients (5 without and 3 with ongoing AZM treatment) and 7 healthy subjects, and J774 cells pre-treated with AZM, a high-molecular-weight derivative of the Fe chelator desferrioxamine or ammonium chloride were oxidatively stressed. LMP, cell death, Fe, reduced glutathione (GSH) and H-ferritin were assessed. RESULTS: Oxidant challenged macrophages from transplants recipients without AZM exhibited significantly more LMP and cell death than macrophages from healthy subjects. Those macrophages contained significantly more Fe, while GSH and H-ferritin did not differ significantly. Although macrophages from transplant recipients treated with AZM contained both significantly more Fe and less GSH, which would sensitize cells to oxidants, these macrophages resisted oxidant challenge well. The preventive effect of AZM on oxidative LMP and J774 cell death was 60 to 300 times greater than the other drugs tested. CONCLUSIONS: AZM makes lung transplant macrophages and their lysososomes more resistant to oxidant challenge. Possibly, prevention of obliterative bronchiolitis in lung transplants by AZM is partly due to this action.

Lung transplantation in the fischer 344-wistar kyoto strain combination is a relevant experimental model to study the development of bronchiolitis obliterans in the rat.

Chronic allograft rejection and bronchiolitis obliterans (BO) limited successful long-term outcome after lung transplantation (LTX). Reliable animal models are needed to study the pathogenesis of BO and to develop effective therapeutic strategies. The relevance of an available experimental LTX model without immunosuppression-the Fischer (F344)-Wistar Kyoto (WKY) rat strain combination-was analyzed. The kinetics of acute and chronic rejection and respective graft histopathology were described in the F344-to-WKY rat strain combination after allogeneic LTX. A modified classification of chronic lung allograft rejection was introduced to describe obliterative changes in the airways after rat LTX. Animals from Harlan Winkelmann (HW) and Charles River (CR) were examined. Within 14 days after LTX, allografts showed moderate to severe acute vascular and bronchiolar inflammation. In contrast to rats from CR, animals from HW showed a delayed acute rejection process. Mid-term phase after LTX (days 20-40) presented a "borderline form" consisting of both acute and first signs of chronic airway rejection. On postoperative day (POD) 60, first signs of airway remodelling and distinct BO were diagnosed in 80% of animals from HW. At the same time, the allografts with BO-like lesions increased up to 100% in rats from CR. The F344-to-WKY rat LTX model allows detailed assessment of all features of acute and chronic pulmonary rejection representing a clinically relevant model. However, due to breeding differences resulting in various sublines of the same rat strain, the source and husbandary history of the animals is important for analysis of immuno-mediated processes.

Increased natural killer T-like cells are a major source of pro-inflammatory cytokines and granzymes in lung transplant recipients.

BACKGROUND AND OBJECTIVE: Natural killer T (NKT)-like cells are a small but significant population of T lymphocytes; however, their role in lung transplant and the effect of current immunosuppressive agents on their function is largely unknown. We have previously shown lung transplant rejection was associated with an increase in peripheral blood T cell γ-interferon (IFN-γ), tumour necrosis factor-α (TNF-α) and granzyme B. NKT-like cells are a source of these pro-inflammatory mediators and as such may be involved in lung transplant pathology. METHODS: We analysed NKT-like cell numbers and cytokine and granzyme profiles in peripheral blood from a group of stable lung transplant patients and control subjects using multiparameter flow cytometry. RESULTS: There was a significant increase in NKT-like cells in transplant patients compared with control subjects (6.8 ± 4.9 vs 0.8 ± 0.2% lymphocytes respectively). There was an increase in the numbers of NKT-like cells producing IFN-γ, TNF-α, IL-2 IL-17, granzyme and perforin in transplant patients compared with controls. Immunosuppressant drugs were less effective at inhibiting IFN-γ and TNF-α production by T and NKT-like cells than NK cells in vitro. CONCLUSIONS: Current therapeutics is inadequate at suppressing NKT-like cell numbers and their production of pro-inflammatory mediators known to be associated with graft rejection. Alternative therapies that specifically target NKT-like cells may improve patient morbidity.

Reciprocal regulation of airway rejection by the inducible gas-forming enzymes heme oxygenase and nitric oxide synthase.

Obliterative bronchiolitis (OB) develops insidiously in nearly half of all lung transplant recipients. Although typically preceded by a CD8(+) T cell-rich lymphocytic bronchitis, it remains unresponsive to conventional immunosuppression. Using an airflow permissive model to study the role of gases flowing over the transplanted airway, it is shown that prolonged inhalation of sublethal doses of carbon monoxide (CO), but not nitric oxide (NO), obliterate the appearance of the obstructive airway lesion. Induction of the enzyme responsible for the synthesis of CO, heme oxygenase (Hmox) 1, increased carboxyhemoglobin levels and suppressed lymphocytic bronchitis and airway luminal occlusion after transplantation. In contrast, zinc protoporphyrin IX, a competitive inhibitor of Hmox, increased airway luminal occlusion. Compared with wild-type allografts, expression of inducible NO synthase (iNOS), which promotes the influx of cytoeffector leukocytes and airway graft rejection, was strikingly reduced by either enhanced expression of Hmox-1 or exogenous CO. Hmox-1/CO decreased nuclear factor (NF)-kappaB binding activity to the iNOS promoter region and iNOS expression. Inhibition of soluble guanylate cyclase did not interfere with the ability of CO to suppress OB, implicating a cyclic guanosine 3',5'-monophosphate-independent mechanism through which CO suppresses NF-kappaB, iNOS transcription, and OB. Prolonged CO inhalation represents a new immunosuppresive strategy to prevent OB.

BLT1-mediated T cell trafficking is critical for rejection and obliterative bronchiolitis after lung transplantation.

Leukotriene B4 is a lipid mediator that recently has been shown to have potent chemotactic activity for effector T lymphocytes mediated through its receptor, BLT1. Here, we developed a novel murine model of acute lung rejection to demonstrate that BLT1 controls effector CD8+ T cell trafficking into the lung and that disruption of BLT1 signaling in CD8+ T cells reduces lung inflammation and mortality in the model. In addition, we used BLT1-deficient mice and a BLT1 antagonist in two tracheal transplant models of lung transplantation to demonstrate the importance of BLT1 for the recruitment of T cells into tracheal allografts. We also show that BLT1-mediated CD8+ T cell recruitment plays an important role in the development of airway fibroproliferation and obliteration. Finally, in human studies of lung transplant recipients, we found that BLT1 is up-regulated on T lymphocytes isolated from the airways of patients with obliterative bronchiolitis. These data demonstrate that BLT1 contributes to the development of lung rejection and obliterative bronchiolitis by mediating effector T lymphocyte trafficking into the lung. This is the first report that describes a pathologic role for BLT1-mediated T lymphocyte recruitment in disease and identifies BLT1 as a potential therapeutic target after lung transplantation.

Pathologic interpretation of transbronchial biopsy for acute rejection of lung allograft is highly variable.

Despite the standardization of pathologic grading of acute rejection in transbronchial lung biopsies following lung transplantation, the reproducibility of pathologic diagnosis has not been adequately evaluated. To determine the interobserver variability for pathologic grading of acute rejection, 1566 biopsies from 845 subjects in the Lung Allograft Rejection Gene Expression Observational study were regraded by a pathology panel blinded to the original diagnosis and compared to the grade of acute rejection assigned by individual center pathologists. The study panel confirmed 49.1% of center pathologists' A0 grades, but upgraded 5.7% to A1 and 2.7% to grade ≥ A2 rejection; 42.5% were regraded as AX. Of 268 grade A1 samples, 21.2% were confirmed by the pathology panel; 18.7% were upgraded to ≥ A2 and 35.8% were downgraded to A0 with 24.3% being regraded as AX. Lastly, 53.5% of ≥ A2 cases were confirmed, but 15.7% were downgraded to grade A0 and 18.4% cases to A1, while 12.4% were regraded as AX. The kappa value for interobserver agreement was 0.183 (95%CI 0.147-0.220, p < 0.001). The results for B grade interpretation were similar. Suboptimal sampling is common and a high degree of variability exists in the pathologic interpretation of acute rejection in transbronchial biopsies.

Bile acids aspiration reduces survival in lung transplant recipients with BOS despite azithromycin.

Azithromycin (AZM) improved bronchiolitis obliterans syndrome (BOS) and reduced aspiration in lung transplant (LTx) recipients. We hypothesize that AZM could improve graft and overall survival more efficiently in LTx patients with BOS who have bile acid (BA) aspiration by protecting against the aspiration-induced progression of BOS. The goal was to compare FEV(1) (% baseline), BOS progression and overall survival in LTx recipients treated with AZM for BOS, both with versus without BA aspiration. Therefore, LTx recipients treated with AZM for BOS were recruited and broncho-alveolar lavage (BAL) samples were analyzed for the presence of BA and neutrophilia before the start of AZM treatment. Short-term effect of AZM on FEV(1) and BAL neutrophilia was assessed, progression of BOS and survival were followed-up for 3 years and results were compared between patients with/without BA aspiration. 19/37 LTx patients had BA in BAL. BA aspiration predisposed to a significantly worse outcome, in terms of decline in FEV(1) , progression of BOS ≥ 1 and survival. AZM does not seem to protect against the long-term allograft dysfunction caused by gastroesophageal reflux (GER) and aspiration and an additional treatment targeting aspiration may be indicated in those LTx patients.

Lung transplantation affects expression of the chemokine receptor type 4 on specific T cell subsets.

Alloreactive T cells that infiltrate the graft after lung transplantation (LTx) play a role in chronic rejection. Chemokines such as thymus and activation-regulated chemokine (TARC), macrophage-derived chemokine (MDC) and monocyte chemotactic protein-1 (MCP-1) are produced locally in the lung and attract T cells via chemokine receptor 4 (CCR4). In a TARC gradient, cells expressing CCR4(++) migrate more efficiently than CCR4(+) -expressing cells. In this study, we compared the CCR4 expression of T cells in blood from 20 lung transplant recipients to healthy controls. We then examined whether CCR4 expression is associated with the occurrence of chronic rejection. The CCR4(++) expression was decreased on CD4 T cells from LTx patients (P < 0·0001) when compared to healthy controls. The analysis of CD4 T cell subsets showed that this decrease was present on central memory, effector memory and terminally differentiated T cells (P = 0·0007, P < 0·0001 and P = 0·05, respectively), while a trend was found for naive CD4 T cells (P = 0·06). Also, the expression of CCR4(+) on regulatory T cells (T(regs) ) was decreased in LTx patients when compared to healthy controls (P = 0·02). Interestingly, the CCR4(++) expression on CD4 effector memory T cells was decreased in patients developing chronic rejection sometimes more than a year before the clinical diagnosis when compared to patients who did not (P = 0·04). The analysis of CD8 T cell subsets only showed the CCR4(+) expression to be increased significantly on effector memory and terminally differentiated CD8 T cells (P = 0·02, P = 0·03, respectively) in LTx patients, but no relation was found in chronic rejection. In conclusion, the expression of CCR4 on T cell subsets was altered after LTx and appears to be related to chronic rejection.

Ischaemia-reperfusion injury in orthotopic mouse lung transplants - a scanning electron microscopy study.

Lung ischaemia-reperfusion (I/R) injury remains a major cause of graft failure in lung transplantation (Tx). With the implementation of orthotopic lung Tx in mice, a physiological model on the base of a perfused and ventilated graft became available for the investigation of I/R injury. Using the scanning electron microscopy (SEM) technique, we here present an analysis of early and late morphological changes of pulmonary I/R injury. Syngeneic lungs were orthotopically transplanted between C57BL/6 mice. Grafts were exposed to 2 h of cold ischaemia. Transplants and right lungs were examined by SEM with corresponding haematoxylin-eosin histology 30 min and 4 h after reperfusion. Thirty minutes after reperfusion, the alveolar surface of transplants showed a discontinued lining of surfactant, while the lining of the non-transplanted lung was normal. Within the graft, leucocytes displayed an irregular surface with development of pseudopodia, and microvilli were detected on the membrane of pneumocytes. At 4 h after reperfusion, leucocytes significantly increased in numbers within the alveolar space. Also, the number of microvilli on pneumocytes increased significantly. Similar to these, the endothelium of vessels increasingly developed microvilli from 30 min towards 4 h after reperfusion. The airways of transplanted grafts showed mild changes with thickening of the bronchial epithelium and a destruction of kinocilia. Taken together, SEM detects pathological events of I/R that are previously not described in normal histology. These findings may influence the interpretation of studies investigating the I/R injury in the mouse model of lung Tx.

Thin-section computed tomography findings before and after azithromycin treatment of neutrophilic reversible lung allograft dysfunction.

OBJECTIVES: Recently a novel subgroup of bronchiolitis obliterans syndrome (BOS) has been described in patients after lung transplantation with high neutrophil counts in broncho-alveolar lavage and recovery of lung functional decline with azithromycin treatment. We aimed to describe the thin-section computed tomography (CT) findings of these neutrophilic reversible allograft dysfunction (NRAD) patients before and after azithromycin. METHODS: A cohort of 100 lung transplant recipients with BOS were treated with azithromycin and underwent lung function testing, broncho-alveolar lavage and CT before azithromycin treatment and during follow-up. The 200 CT data sets were scored for bronchial dilatation, mucus plugging, centrilobular abnormalities, airway wall thickening, consolidation, ground glass and end-expiratory air trapping. RESULTS: NRAD was characterized by more centrilobular abnormalities on CT (p = 0.03 for prevalence and p = 0.06 for severity) compared to non-responders. At follow-up NRAD patients showed improvement in all CT abnormalities including air trapping, but the degree of improvement in all CT abnormalities was significantly different between responders and non-responders (who showed progression of bronchus dilatation, consolidation and air trapping). CONCLUSIONS: Within BOS patients those with NRAD differ from azithromycin non-responders by more centrilobular abnormalities on CT before azithromycin and improvement in bronchus dilatation, consolidation and air trapping during treatment.

Antibodies to MHC class I induce autoimmunity: role in the pathogenesis of chronic rejection.

Alloimmunity to mismatched donor HLA-Ags and autoimmunity to self-Ags have been hypothesized to play an important role in immunopathogenesis of chronic rejection of transplanted organs. However, it is not known what role, if any, alloimmune response plays in inducing autoimmunity. To test whether Ab-developed posttransplantation to mismatched donor MHC induces autoimmunity and chronic rejection, we developed a murine model wherein anti-MHC class I Abs or control (C1.18.4/anti-keratin) were administered intrabronchially into native lungs. Animals receiving anti-MHC class I, but not control Abs, developed marked cellular infiltration around vessels and bronchiole of lung by day 15, followed by epithelial hyperplasia, fibrosis, and occlusion of the distal airways similar to chronic rejection following human lung transplantation. Lungs of mice receiving anti-MHC class I showed increased expression of chemokines, their receptors, and growth factors, and induced IL-17 as well as de novo Abs to self-Ags, K-alpha1 tubulin, and collagen V. IL-17 neutralization by anti-IL-17 resulted in reduction of autoantibody and lesions induced by anti-MHC class I Abs. Thus, our results indicate that Abs to donor MHC can induce autoimmunity, mediated by IL-17, which plays a pivotal role in chronic rejection postlung transplantation. Therefore, approaches to prevent autoimmunity should be considered for the treatment of chronic rejection postlung transplantation.

Type V collagen-induced oral tolerance plus low-dose cyclosporine prevents rejection of MHC class I and II incompatible lung allografts.

Autoimmunity to type V collagen (col(V)) is a major risk factor for lung allograft rejection. Although col(V)-induced oral tolerance abrogates rejection of minor histoincompatible lung transplants, its ability to prevent rejection of fully MHC incompatible lung allografts is unknown. Rat lung allografts fully incompatible at MHC class I and II loci (Brown Norway (RT1(n))) were transplanted into untreated Wistar Kyoto rat recipients (WKY, RT1(l)), or WKY rats were fed col(V) pretransplantation. To determine whether col(V) enhanced cyclosporine (CsA)-mediated immune suppression, WKY rats were treated with low-dose CsA (5 mg/kg), posttransplant, or oral col(V) plus CsA. The data showed that in contrast to col(V) or CsA, col(V) plus low-dose CsA significantly prevented rejection pathology, down-regulated alloantigen-induced production of IFN-gamma and IL-17A, and suppressed chemotaxis for lung macrophages in allograft bronchoalveolar lavage fluid that was associated with lower local levels of MCP-1 (CCL2). Col(V) plus CsA was associated with alloantigen-induced expression of IL-10 in mediastinal lymph node or splenic T cells, intragraft expression of IL-10 and Foxp3 in perivascular and peribronchiolar mononuclear cells, and constitutive production of IL-10 from allograft alveolar macrophages. These data demonstrate that col(V) enhances low-dose CsA-mediated immune suppression, and suggest a role for oral col(V) in immune modulation in lung transplantation.

[Lung transplantation and rejection. Basic principles, clinical aspects and histomorphology]. / Lungentransplantation und Abstoßung. Grundlagen, klinische Aspekte und Histomorphologie.

Lung transplantation is the ultimate therapeutical approach for the treatment of both children and adults with terminal congenital or acquired lung disease. In contrast to survival rates during the first year following transplantation, the long-term survival for patients after lung transplantation has not significantly improved in the past. In addition to other complications, acute cellular rejection constitutes a major cause for diminished function of pulmonary grafts, and can, among other factors, be causative for chronic rejection (bronchiolitis obliterans syndrome, BOS). In 2006, the International Society for Heart and Lung Transplantation (ISHLT) provided a revised version of the grading system for acute and chronic rejection of pulmonary grafts.

IL-17-dependent cellular immunity to collagen type V predisposes to obliterative bronchiolitis in human lung transplants.

Bronchiolitis obliterans syndrome (BOS), a process of fibro-obliterative occlusion of the small airways in the transplanted lung, is the most common cause of lung transplant failure. We tested the role of cell-mediated immunity to collagen type V [col(V)] in this process. PBMC responses to col(II) and col(V) were monitored prospectively over a 7-year period. PBMCs from lung transplant recipients, but not from healthy controls or col(IV)-reactive Goodpasture's syndrome patients after renal transplant, were frequently col(V) reactive. Col(V)-specific responses were dependent on both CD4+ T cells and monocytes and required both IL-17 and the monokines TNF-alpha and IL-1beta. Strong col(V)-specific responses were associated with substantially increased incidence and severity of BOS. Incidences of acute rejection, HLA-DR mismatched transplants, and induction of HLA-specific antibodies in the transplant recipient were not as strongly associated with a risk of BOS. These data suggest that while alloimmunity initiates lung transplant rejection, de novo autoimmunity mediated by col(V)-specific Th17 cells and monocyte/macrophage accessory cells ultimately causes progressive airway obliteration.

Every allograft needs a silver lining.

The development of chronic allograft rejection is based on the hypothesis that cumulative, time-dependent tissue injury eventually leads to a fibrotic response. In this issue of the JCI, Babu and colleagues found that alloimmune-mediated microvascular loss precedes tissue damage in murine orthotopic tracheal allografts (see the related article beginning on page 3774). The concept that injury to the endothelium may precede airway fibrosis suggests that interventions to maintain vascular integrity may be important, especially in the case of lung transplantation. Further, for all solid organ allografts, it is possible that the key to long-term allograft survival is physiological vascular repair at early times following transplantation.