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Bos S, Milross L, Filby AJ, Vos R, Fisher AJ. Immune processes in the pathogenesis of chronic lung allograft dysfunction: identifying the missing pieces of the puzzle. Eur Respir Rev 2022; 31:31/165/220060. [PMID: 35896274 DOI: 10.1183/16000617.0060-2022] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2022] [Accepted: 05/19/2022] [Indexed: 11/05/2022] Open
Abstract
Lung transplantation is the optimal treatment for selected patients with end-stage chronic lung diseases. However, chronic lung allograft dysfunction remains the leading obstacle to improved long-term outcomes. Traditionally, lung allograft rejection has been considered primarily as a manifestation of cellular immune responses. However, in reality, an array of complex, interacting and multifactorial mechanisms contribute to its emergence. Alloimmune-dependent mechanisms, including T-cell-mediated rejection and antibody-mediated rejection, as well as non-alloimmune injuries, have been implicated. Moreover, a role has emerged for autoimmune responses to lung self-antigens in the development of chronic graft injury. The aim of this review is to summarise the immune processes involved in the pathogenesis of chronic lung allograft dysfunction, with advanced insights into the role of innate immune pathways and crosstalk between innate and adaptive immunity, and to identify gaps in current knowledge.
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Affiliation(s)
- Saskia Bos
- Newcastle University Translational and Clinical Research Institute, Newcastle upon Tyne, UK.,Institute of Transplantation, Newcastle upon Tyne Hospitals NHS Trust, Newcastle upon Tyne, UK
| | - Luke Milross
- Newcastle University Translational and Clinical Research Institute, Newcastle upon Tyne, UK
| | - Andrew J Filby
- Flow Cytometry Core and Innovation, Methodology and Application Research Theme, Biosciences Institute, Newcastle University, Newcastle upon Tyne, UK
| | - Robin Vos
- Dept of CHROMETA, Laboratory of Respiratory Diseases and Thoracic Surgery (BREATHE), KU Leuven, Leuven, Belgium.,University Hospitals Leuven, Dept of Respiratory Diseases, Leuven, Belgium
| | - Andrew J Fisher
- Newcastle University Translational and Clinical Research Institute, Newcastle upon Tyne, UK .,Institute of Transplantation, Newcastle upon Tyne Hospitals NHS Trust, Newcastle upon Tyne, UK
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Flanagan F, Casey A, Reyes-Múgica M, Kurland G. Post-infectious bronchiolitis obliterans in children. Paediatr Respir Rev 2022; 42:69-78. [PMID: 35562287 DOI: 10.1016/j.prrv.2022.01.007] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/19/2022] [Accepted: 01/28/2022] [Indexed: 10/19/2022]
Affiliation(s)
- Frances Flanagan
- Division of Pulmonary Medicine, Boston Children's Hospital, 333 Longwood Ave, 5(th) Floor, Boston, MA 02115, United States.
| | - Alicia Casey
- Division of Pulmonary Medicine, Boston Children's Hospital, 333 Longwood Ave, 5(th) Floor, Boston, MA 02115, United States.
| | - Miguel Reyes-Múgica
- Department of Pathology, UPMC Children's Hospital ofPittsburgh, One Children's Hospital Drive, 4401 Penn Avenue, Pittsburgh PA 1522, United States.
| | - Geoffrey Kurland
- Division of Pediatric Pulmonology, UPMC Children's Hospital of Pittsburgh, 4401 Penn Avenue, Pittsburgh, PA 15224, United States.
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Abstract
Chronic lung allograft dysfunction (CLAD) is a syndrome of progressive lung function decline, subcategorized into obstructive, restrictive, and mixed phenotypes. The trajectory of CLAD is variable depending on the phenotype, with restrictive and mixed phenotypes having more rapid progression and lower survival. The mechanisms driving CLAD development remain unclear, though allograft injury during primary graft dysfunction, acute cellular rejection, antibody-mediated rejection, and infections trigger immune responses with long-lasting effects that can lead to CLAD months or years later. Currently, retransplantation is the only effective treatment.
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Affiliation(s)
- Aida Venado
- Division of Pulmonary, Critical Care, Allergy, and Sleep Medicine, University of California, San Francisco, 505 Parnassus Ave, M1093A, San Francisco, CA 94143-2204, USA.
| | - Jasleen Kukreja
- Division of Cardiothoracic Surgery, Univeristy of California, San Francisco, 500 Parnassus Ave, MU 405W Suite 305, San Francisco, CA 94143, USA
| | - John R Greenland
- Division of Pulmonary, Critical Care, Allergy, and Sleep Medicine, University of California, San Francisco, SF VAHCS Building 2, Room 453 (Mail stop 111D), 4150 Clement St, San Francisco CA 94121, USA
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4
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Interleukin-18: A Novel Participant in the Occurrence, Development, and Drug Therapy of Obliterative Bronchiolitis Postlung Transplantation. DISEASE MARKERS 2021; 2021:5586312. [PMID: 34367377 PMCID: PMC8337162 DOI: 10.1155/2021/5586312] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/26/2021] [Accepted: 07/15/2021] [Indexed: 12/03/2022]
Abstract
Background Obliterative bronchiolitis (OB) was a main cause of deterioration of long-term prognosis in lung transplant recipients after the first posttransplant year. Proinflammatory cytokine interleukin-18 (IL-18) strengthened both the natural immunity and acquired immunity and played an important role in organ transplantation. The roles of IL-18 in the occurrence, development, and drug treatment of OB remained unclear. Methods Small interfering RNA (siRNA) against mouse IL-18 (siRNA-IL-18) was used to silence IL-18 expression. Mouse heterotopic tracheal transplantation model was used to simulate OB. Recipient mice were divided into 5 groups (n = 12) according to donor mouse strains and drug treatment: isograft group, allograft group, allograft+tacrolimus group, allograft+azithromycin group, and allograft+tacrolimus+azithromycin group. The luminal obliteration rates were pathological evaluation. Expressions of cytokines and MMPs were detected by real-time PCR, western blot, and enzyme chain immunosorbent assay (ELISA). Results The luminal obliteration rates of IL-18 of the siRNA-IL-18 group were significantly lower than those of the negative control group (p < 0.0001) and the blank control group (p = 0.0002). mRNA expressions of IFN-γ, EMMPRIN, MMP-8, and MMP-9 of the siRNA-IL-18 group were significantly lower than those of the negative and blank control groups. No tracheal occlusion occurred in grafts of the isograft group. The rates of tracheal occlusion of the allograft group, allograft+tacrolimus group, allograft+azithromycin group, and allograft+tacrolimus+azithromycin group were 72.17 ± 4.66%, 40.33 ± 3.00%, 38.50 ± 2.08%, and 23.33 ± 3.24%, respectively. There were significant differences between the 4 groups (p < 0.001). Serum protein expressions of IL-17 (p = 0.0017), IL-18 (p = 0.0036), IFN-γ (p = 0.0102), and MMP-9 (p = 0.0194) were significantly decreased in the allograft+tacrolimus+azithromycin group compared to the allograft group. Conclusions IL-18 could be a novel molecular involved in the occurrence, development, and drug treatment of OB.
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Yoshiyasu N, Sato M. Chronic lung allograft dysfunction post-lung transplantation: The era of bronchiolitis obliterans syndrome and restrictive allograft syndrome. World J Transplant 2020; 10:104-116. [PMID: 32864356 PMCID: PMC7428788 DOI: 10.5500/wjt.v10.i5.104] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/24/2020] [Revised: 04/30/2020] [Accepted: 05/12/2020] [Indexed: 02/05/2023] Open
Abstract
Chronic lung allograft dysfunction (CLAD) following lung transplantation limits long-term survival considerably. The main reason for this is a lack of knowledge regarding the pathological condition and the establishment of treatment. The consensus statement from the International Society for Heart and Lung Transplantation on CLAD in 2019 classified CLAD into two main phenotypes: Bronchiolitis obliterans syndrome and restrictive allograft syndrome. Along with this clear classification, further exploration of the mechanisms and the development of appropriate prevention and treatment strategies for each phenotype are desired. In this review, we summarize the new definition of CLAD and update and summarize the existing knowledge on the underlying mechanisms of bronchiolitis obliterans syndrome and restrictive allograft syndrome, which have been elucidated from clinicopathological observations and animal experiments worldwide.
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Affiliation(s)
- Nobuyuki Yoshiyasu
- Department of Thoracic Surgery, The University of Tokyo Hospital, Tokyo 113-8655, Japan
| | - Masaaki Sato
- Department of Thoracic Surgery, The University of Tokyo Hospital, Tokyo 113-8655, Japan
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Kawashima M, Juvet SC. The role of innate immunity in the long-term outcome of lung transplantation. ANNALS OF TRANSLATIONAL MEDICINE 2020; 8:412. [PMID: 32355856 PMCID: PMC7186608 DOI: 10.21037/atm.2020.03.20] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Long-term survival after lung transplantation remains suboptimal due to chronic lung allograft dysfunction (CLAD), a progressive scarring process affecting the graft. Although anti-donor alloimmunity is central to the pathogenesis of CLAD, its underlying mechanisms are not fully elucidated and it is neither preventable nor treatable using currently available immunosuppression. Recent evidence has shown that innate immune stimuli are fundamental to the development of CLAD. Here, we examine long-standing assumptions and new concepts linking innate immune activation to late lung allograft fibrosis.
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Affiliation(s)
- Mitsuaki Kawashima
- Latner Thoracic Research Laboratories, University Health Network, University of Toronto, Toronto, Ontario, Canada
| | - Stephen C Juvet
- Latner Thoracic Research Laboratories, University Health Network, University of Toronto, Toronto, Ontario, Canada
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Calabrese DR, Wang P, Chong T, Hoover J, Singer JP, Torgerson D, Hays SR, Golden JA, Kukreja J, Dugger D, Christie JD, Greenland JR. Dectin-1 genetic deficiency predicts chronic lung allograft dysfunction and death. JCI Insight 2019; 4:133083. [PMID: 31613800 DOI: 10.1172/jci.insight.133083] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2019] [Accepted: 10/10/2019] [Indexed: 12/21/2022] Open
Abstract
BACKGROUNDInnate immune activation impacts lung transplant outcomes. Dectin-1 is an innate receptor important for pathogen recognition. We hypothesized that genotypes reducing dectin-1 activity would be associated with infection, graft dysfunction, and death in lung transplant recipients.METHODSWe assessed the rs16910526 CLEC7A gene polymorphism Y238X, which results in dectin-1 truncation, in 321 lung allograft recipients at a single institution and in 1,129 lung allograft recipients in the multicenter Lung Transplant Outcomes Group (LTOG) cohort. Differences in dectin-1 mRNA, cytokines, protein levels, immunophenotypes, and clinical factors were assessed.RESULTSY238X carriers had decreased dectin-1 mRNA expression (P = 0.0001), decreased soluble dectin-1 protein concentrations in bronchoalveolar lavage (P = 0.008) and plasma (P = 0.04), and decreased monocyte surface dectin-1 (P = 0.01) compared with wild-type subjects. Y238X carriers had an increased risk of fungal pathogens (HR 1.17, CI 1.0-1.4), an increased risk of graft dysfunction or death (HR 1.6, CI 1.0-2.6), as well increased mortality in the UCSF cohort (HR 1.8, CI 1.1-3.8) and in the LTOG cohort (HR 1.3, CI 1.1-1.6), compared with wild-type CLEC7A subjects.CONCLUSIONIncreased rates of graft dysfunction and death associated with this dectin-1 polymorphism may be amplified by immunosuppression that drives higher fungal burden from compromised pathogen recognition.FUNDINGThe UCSF Nina Ireland Program for Lung Health Innovative Grant program, the Clinical Sciences Research & Development Service of the VA Office of Research and Development, and the Joel D. Cooper Career Development Award from the International Society for Heart and Lung Transplantation.
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Affiliation(s)
- Daniel R Calabrese
- Department of Medicine, UCSF, San Francisco, California, USA.,Medical Service, Veterans Affairs Health Care System, San Francisco, California, USA
| | - Ping Wang
- Department of Medicine, UCSF, San Francisco, California, USA
| | - Tiffany Chong
- Department of Medicine, UCSF, San Francisco, California, USA
| | - Jonathan Hoover
- Department of Medicine, UCSF, San Francisco, California, USA
| | | | - Dara Torgerson
- Department of Medicine, UCSF, San Francisco, California, USA
| | - Steven R Hays
- Department of Medicine, UCSF, San Francisco, California, USA
| | | | | | - Daniel Dugger
- Medical Service, Veterans Affairs Health Care System, San Francisco, California, USA
| | - Jason D Christie
- Department of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | | | - John R Greenland
- Department of Medicine, UCSF, San Francisco, California, USA.,Medical Service, Veterans Affairs Health Care System, San Francisco, California, USA
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Li Y, Shu P, Tang L, Yang X, Fan J, Zhang X. FK506 combined with GM6001 prevents tracheal obliteration in a mouse model of heterotopic tracheal transplantation. Transpl Immunol 2019; 57:101244. [PMID: 31526865 DOI: 10.1016/j.trim.2019.101244] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2019] [Revised: 09/08/2019] [Accepted: 09/13/2019] [Indexed: 01/02/2023]
Abstract
BACKGROUND Obliterative bronchiolitis (OB) is the major complication limiting the long-term survival of allografts after lung transplantation. In this study, we investigated the effect of tacrolimus (FK506) combined with GM6001,a matrix metalloproteinase (MMP) inhibitor, on the formation of OB using a mouse heterotopic tracheal transplantation model. METHODS Syngeneic tracheal grafts were transplanted heterotopically from BALB/c mice to BALB/c mice. Allografts from C57BL/6 mice were transplanted to BALB/c mice. Isograft group, allograft group, allograft+FK506 group, allograft +GM6001 group and allograft+FK506 + GM6001 group was given respectively intraperitoneal injection of saline, saline, FK506, GM6001 and FK506 + GM6001 once a day. At 28 day after transplantation, OB incidence was determined by hematoxylin-eosin staining and the expressions of MMPs and cytokines were assessed using enzyme linked immunosorbent assay, immunohistochemical assays and western blot assay. RESULTS The tracheal occlusion rates of isograft group, allograft group, allograft+FK506 group, allograft+GM6001 group and allograft+FK506 + GM6001 group were 0, 74.1 ± 9.79%, 34.4 ± 6.04%, 40.3 ± 8.77% and 26.5 ± 5.73% respectively. There were significant differences between the latter two groups (P < .001). The serum MMP-8 and MMP-9 levels of allograft group were significantly higher than those of isograft group (P < .05) and had no significant decrease when treated by FK506. The serum MMP-8 and MMP-9 levels of allograft+FK506 + GM6001 group were significantly lower than those of allograft+FK506 group (P < .05). MMP-8 and MMP-9 protein expression in the grafts of allograft+FK506 + GM6001 group were lower than those of allograft+FK506 group verified by immunohistochemical staining and western blotting. CONCLUSION FK506 combined with GM6001 could alleviate tracheal obliteration in mouse heterotopic tracheal transplantation model, due to its inhibitory effect on MMPs.
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Affiliation(s)
- Yiqian Li
- Department of pharmacy, Shanghai Pulmonary Hospital, Tongji University, Shanghai, China
| | - Ping Shu
- Department of pharmacy, Shanghai Pulmonary Hospital, Tongji University, Shanghai, China
| | - Liang Tang
- Department of central Laboratory, Shanghai Pulmonary Hospital, Tongji University, Shanghai, China
| | - Xiaojun Yang
- Department of central Laboratory, Shanghai Pulmonary Hospital, Tongji University, Shanghai, China
| | - Junwei Fan
- Department of general Surgery, Shanghai General Hospital Affiliated to Shanghai Jiao Tong University, Shanghai, China.
| | - Xiaoqing Zhang
- Department of pharmacy, Shanghai Pulmonary Hospital, Tongji University, Shanghai, China; The International Peace Maternity and Child Health Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China; Shanghai Key Laboratory of Embryo Original Diseases, Shanghai, China; Shanghai Municipal Key Clinical Specialty, Shanghai, China.
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Precision medicine: integration of genetics and functional genomics in prediction of bronchiolitis obliterans after lung transplantation. Curr Opin Pulm Med 2019; 25:308-316. [PMID: 30883449 DOI: 10.1097/mcp.0000000000000579] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
PURPOSE OF REVIEW Lung transplantation (LTx) can be a life saving treatment in end-stage pulmonary diseases, but survival after transplantation is still limited. Posttransplant development of chronic lung allograft dysfunction with bronchiolits obliterans syndrome (BOS) as the major subphenotype, is the main cause of morbidity and mortality. Early identification of high-risk patients for BOS is a large unmet clinical need. In this review, we discuss gene polymorphisms and gene expression related to the development of BOS. RECENT FINDINGS Candidate gene studies showed that donor and recipient gene polymorphisms affect transplant outcome and BOS-free survival after LTx. Both selective and nonselective gene expression studies revealed differentially expressed fibrosis and apoptosis-related genes in BOS compared with non-BOS patients. Significantly, recent microarray expression analysis of blood and broncho-alveolar lavage suggest a role for B-cell and T-cell responses prior to the development of BOS. Furthermore, 6 months prior to the development of BOS differentially expressed genes were identified in peripheral blood cells. SUMMARY Genetic polymorphisms and gene expression changes are associated with the development of BOS. Future genome wide studies are needed to identify easily accessible biomarkers for prediction of BOS toward precision medicine.
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Abstract
PURPOSE OF REVIEW Chronic lung allograft dysfunction (CLAD) was recently introduced as an overarching term covering different phenotypes of chronic allograft dysfunction, including obstructive CLAD (bronchiolitis obliterans syndrome), restrictive CLAD (restrictive allograft syndrome) and graft dysfunction due to causes not related to chronic rejection. In the present review, we will highlight the latest insights and current controversies regarding the new CLAD terminology, underlying pathophysiologic mechanisms, diagnostic approach and possible treatment options. RECENT FINDINGS Different pathophysiological mechanisms are clearly involved in clinically distinct phenotypes of chronic rejection, as is reflected by differences in histology, allograft function and imaging. Therefore, not all CLAD patients may equally benefit from specific therapies. SUMMARY The recent introduction of CLAD importantly changed the clinical practice in lung transplant recipients. Given the relative low accuracy of the current diagnostic tools, future research should focus on specific biomarkers, more sensitive pulmonary function parameters and imaging techniques for timely CLAD diagnosis and phenotyping. Personalized or targeted therapeutic options for adequate prevention and treatment of CLAD are required.
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12
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Evers A, Atanasova S, Fuchs-Moll G, Petri K, Wilker S, Zakrzewicz A, Hirschburger M, Padberg W, Grau V. Adaptive and innate immune responses in a rat orthotopic lung transplant model of chronic lung allograft dysfunction. Transpl Int 2014; 28:95-107. [PMID: 25179205 DOI: 10.1111/tri.12444] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2014] [Revised: 07/20/2014] [Accepted: 08/28/2014] [Indexed: 01/15/2023]
Abstract
Acute rejection and respiratory infections are major risk factors for chronic lung allograft dysfunction (CLAD) after lung transplantation. To shed light on the enigmatic etiology of CLAD, we test the following hypotheses using a new experimental model: (i) Alloimmune-independent pulmonary inflammation reactivates alloimmunity. (ii) Alloimmunity enhances the susceptibility of the graft toward pathogen-associated molecular patterns. Pulmonary Fischer 344 to Lewis rat allografts were treated with lipopolysaccharide (LPS), which consistently results in lesions typical for CLAD. Grafts, local lymph nodes, and spleens were harvested before (day 28) and after LPS application (days 29, 33, and 40) for real-time RT-PCR and immunohistochemistry. Mixed lymphocyte reactions were performed on day 33. Four weeks after transplantation, lung allografts displayed mononuclear infiltrates compatible with acute rejection and overexpressed most components of the toll-like receptor system. Allografts but not secondary lymphoid organs expressed increased levels of Th1-type transcription factors and cytokines. LPS induced macrophage infiltration as well as mRNA expression of pro-inflammatory cytokines and effector molecules of innate immunity. Unexpectedly, T-cell reactivity was not enhanced by LPS. We conclude that prevention of CLAD might be accomplished by local suppression of Th1 cells in stable grafts and by controlling innate immunity during alloimmune-independent pulmonary inflammation.
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Affiliation(s)
- Alena Evers
- Laboratory of Experimental Surgery, Department of General and Thoracic Surgery, Member of the German Centre for Lung Research, Justus-Liebig-University Giessen, Giessen, Germany
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Diamond JM, Akimova T, Kazi A, Shah RJ, Cantu E, Feng R, Levine MH, Kawut SM, Meyer NJ, Lee JC, Hancock WW, Aplenc R, Ware LB, Palmer SM, Bhorade S, Lama VN, Weinacker A, Orens J, Wille K, Crespo M, Lederer DJ, Arcasoy S, Demissie E, Christie JD. Genetic variation in the prostaglandin E2 pathway is associated with primary graft dysfunction. Am J Respir Crit Care Med 2014; 189:567-75. [PMID: 24467603 DOI: 10.1164/rccm.201307-1283oc] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
RATIONALE Biologic pathways with significant genetic conservation across human populations have been implicated in the pathogenesis of primary graft dysfunction (PGD). The evaluation of the role of recipient genetic variation in PGD has thus far been limited to single, candidate gene analyses. OBJECTIVES We sought to identify genetic variants in lung transplant recipients that are responsible for increased risk of PGD using a two-phase large-scale genotyping approach. METHODS Phase 1 was a large-scale candidate gene association study of the multicenter, prospective Lung Transplant Outcomes Group cohort. Phase 2 included functional evaluation of selected variants and a bioinformatics screening of variants identified in phase 1. MEASUREMENTS AND MAIN RESULTS After genetic data quality control, 680 lung transplant recipients were included in the analysis. In phase 1, a total of 17 variants were significantly associated with PGD, four of which were in the prostaglandin E2 family of genes. Among these were a coding variant in the gene encoding prostaglandin E2 synthase (PTGES2; P = 9.3 × 10(-5)) resulting in an arginine to histidine substitution at amino acid position 298, and three variants in a block containing the 5' promoter and first intron of the PTGER4 gene (encoding prostaglandin E2 receptor subtype 4; all P < 5 × 10(-5)). Functional evaluation in regulatory T cells identified that rs4434423A in the PTGER4 gene was associated with differential suppressive function of regulatory T cells. CONCLUSIONS Further research aimed at replication and additional functional insight into the role played by genetic variation in prostaglandin E2 synthetic and signaling pathways in PGD is warranted.
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