Association Between Donor MBL Promoter Haplotype and Graft Survival and the Development of BOS After Lung Transplantation

Recent advances into the role of pattern recognition receptors in transplantation

Pattern recognition receptors (PRRs) are germline-encoded sensors best characterized for their critical role in host defense. However, there is accumulating evidence that organ transplantation induces the release or display of molecular patterns of cellular injury and death that trigger PRR-mediated inflammatory responses. There are also new insights that indicate PRRs are able to distinguish between self and non-self, suggesting the existence of non-clonal mechanisms of allorecognition. Collectively, these reports have spurred considerable interest into whether PRRs or their ligands can be targeted to promote transplant survival. This review examines the mounting evidence that PRRs play in transplant-mediated inflammation. Given the large number of PRRs, we will focus on members from four families: the complement system, toll-like receptors, the formylated peptide receptor, and scavenger receptors through examining reports of their activity in experimental models of cellular and solid organ transplantation as well as in the clinical setting.

Impact of MBL2 gene polymorphisms on the risk of infection in solid organ transplant recipients: A systematic review and meta-analysis

Mannose-binding lectin (MBL) is a soluble pattern recognition molecule involved in complement activation. Single nucleotide polymorphisms (SNPs) in the MBL2 gene have been associated with susceptibility to infection, although data in solid organ transplant recipients remains inconclusive. This meta-analysis was primarily aimed at investigating the association between posttransplant bacterial and fungal infection and variant alleles of MBL2 gene SNPs in the promoter/5' untranslated region and exon 1. Cytomegalovirus (CMV) infection and/or disease were considered secondary outcomes. PubMed, EMBASE, and Web of Knowledge were searched for relevant articles up to August 2018. Eleven studies (comprising 1858 patients) were included, with liver transplant (LT) recipients accounting for 80.4% of the pooled population. As compared to high-MBL expression haplotypes (YA/YA, YA/XA), any MBL-deficient haplotype was associated with an increased risk of posttransplant bacterial and fungal infections (risk ratio [RR]: 1.30; P = .04). Low/null-MBL expression haplotypes (XA/O, O/O) also increased the risk of primary outcome (RR: 1.51; P = .008) and CMV events (RR: 1.50; P = .006). No effect was observed for individual promoter SNPs. In conclusion, MBL-deficient haplotypes are associated with a significant, albeit moderate, increase in the risk of posttransplant infection, with this association being mainly restricted to LT recipients.

Association between a Single Donor TARC/CCL17 Promotor Polymorphism and Obstructive Chronic Lung Allograft Dysfunction after Lung Transplantation

Lung transplantation (LTx) outcome is hampered by development of chronic rejection, often manifested as the bronchiolitis obliterans syndrome (BOS). Low serum levels of thymus and activation-regulated chemokine (TARC/CCL17), a chemoattractant, measured during the first month post-LTx are predictive for BOS development. Since TARC/CCL17 promotor polymorphisms correlate with serum TARC/CCL17 levels, we investigated seven single-nucleotide polymorphisms (SNPs) within this region and their potential association with LTx outcome. We analyzed donor and patient SNP configurations and haplotypes and observed a trend between a donor SNP (rs223899) configuration and patient TARC/CCL17 serum levels post-LTx (p = 0.066). Interestingly, this SNP configuration in patients did not show any correlation with pre-LTx TARC/CCL17 serum levels (p = 0.776). Survival analysis showed that receiving a graft from a donor heterozygous for rs223899 has a disadvantageous impact on transplantation outcome. When stratified per donor SNP genotype, patients receiving a transplant from a heterozygous donor showed a lower BOS-free survival (p = 0.023) and survival rate (p = 0.0079). Since rs223899 is located within a NFκB binding site, heterozygosity at this position could result in a reduced TARC/CCL17 expression. Our data indicate that a single TARC/CCL17 promotor SNP in the donor correlates with lower serum TARC/CCL17 levels measured 1 month after LTx and affects clinical outcome after LTx.

Systematic assessment of the influence of complement gene polymorphisms on kidney transplant outcome

The importance of the innate immune system, including complement, in causing transplant injury and augmenting adaptive immune responses is increasingly recognized. Therefore variability in graft outcome may in part be due to genetic polymorphism in genes encoding proteins of the immune system. This study assessed the relationship between single nucleotide polymorphisms (SNPs) in complement genes and outcome after transplantation. Analysis was performed on two patient cohorts of 650 and 520 transplant recipients. 505 tagged SNPs in 47 genes were typed in both donor and recipient. The relationships between SNPs and graft survival, serum creatinine, delayed graft function and acute rejection were analyzed. One recipient SNP in the gene encoding mannose binding lectin was associated with graft outcome after correction for analysis of multiple SNPs (p=6.41 × 10(-5)). When further correction was applied to account for analysis of the effect of SNPs in both donor and recipient this lost significance. Despite association p values of <0.001 no SNP was significantly associated with clinical phenotypes after Bonferroni correction. In conclusion, the variability seen in transplant outcome in this patient cohort cannot be explained by variation in complement genes. If causal genetic effects exist in these genes, they are too small to be detected by this study.

Role of genetics in lung transplant complications

There is increasing knowledge that patients can be predisposed to a certain disease by genetic variations in their DNA. Extensive genetic variation has been described in molecules involved in short- and long-term complications after lung transplantation (LTx), such as primary graft dysfunction (PGD), acute rejection, respiratory infection, chronic lung allograft dysfunction (CLAD), and mortality. Several of these studies could not be confirmed or were not reproduced in other cohorts. However, large multicenter prospective studies need to be performed to define the real clinical consequence and significance of genotyping the donor and receptor of a LTx. The current review presents an overview of genetic polymorphisms (SNP) investigating an association with different complications after LTx. Finally, the major drawbacks, clinical relevance, and future perspectives will be discussed.

Mannan-binding lectin in cardiovascular disease

Cardiovascular disease remains the leading cause of mortality and morbidity worldwide so research continues into underlying mechanisms. Since innate immunity and its potent component mannan-binding lectin have been proven to play an important role in the inflammatory response during infection and ischaemia-reperfusion injury, attention has been paid to its role in the development of cardiovascular complications as well. This review provides a general outline of the structure and genetic polymorphism of MBL and its role in inflammation/tissue injury with emphasis on associations with cardiovascular disease. MBL appears to be involved in the pathogenesis of atherosclerosis and, in consequence, coronary artery disease and also inflammation and tissue injury after myocardial infarction and heart transplantation. The relationship between MBL and disease is rather complex and depends on different genetic and environmental factors. That could be why the data obtained from animal and clinical studies are sometimes contradictory proving not for the first time that innate immunity is a "double-edge sword," sometimes beneficial and, at other times disastrous for the host.

Genetic variation in the prostaglandin E2 pathway is associated with primary graft dysfunction

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.

Characterization of mannose-binding lectin (MBL) variants by allele-specific sequencing of MBL2 and determination of serum MBL protein levels

Mannose-binding lectin (MBL) is a major component of the lectin pathway of complement activation. High and low MBL levels have been associated with susceptibility and severity of a variety of infectious and autoimmune diseases. Several single-nucleotide polymorphisms (SNPs) in the promoter region and exon 1 of the MBL2 gene are responsible for variations in serum MBL levels. We developed a sequence-based typing method for allele-specific MBL2 genotyping and measured serum MBL protein levels in 24 German blood donors. We identified the common MBL2 haplotypes including five promoter polymorphisms in linkage with the Q allele and correlated serum MBL levels with the respective genotypes. The genotyping method presented here could provide a basis for confirmatory studies in larger cohorts.

Emerging role of the mannose-binding lectin-dependent pathway of complement activation in clinical organ transplantation

PURPOSE OF REVIEW

Over the past decade, the role of the complement system in solid organ transplantation has received increased attention. A number of experimental and epidemiological studies have suggested that the lectin pathway plays a role in infectious complications, rejection and long-term outcome after transplantation. This review discusses recent data on the role of the lectin pathway in solid organ transplantation.

RECENT FINDINGS

Studies on the role of mannose-binding lectin (MBL) in organ transplantation have shown an association of MBL-deficient states with an increased risk of infection after liver and simultaneous pancreas-kidney transplantation. On the contrary, a high MBL status in the recipient has been associated with poorer organ survival and increased rejection associated damage in various transplant settings. Experimental data points towards a role for MBL in ischemia-reperfusion damage in various organs. Several lines of evidence suggest that MBL may contribute to immunoglobulin-mediated complement activation in both ischemia-reperfusion and rejection. The interaction of MBL with IgM may be of particular importance in this setting.

SUMMARY

We review recent epidemiological data on the role of MBL in solid organ transplantation. We relate these findings to the emerging experimental data and attempt to explain some of the conflicting results on beneficial and harmful effects of the lectin pathway.

Mannose binding lectin (mbl2) haplotype frequencies in solid organ transplant patients and correlation with MBL protein levels--evaluation of complement-mediated effector pathway deficiency

Mannose-binding lectin (MBL) is a protein critical in activating complement. Patients with wild-type and variant mbl2 genotypes have high or low concentrations of MBL protein, which is known to increase susceptibility to transplant rejection or infection, respectively. Our objective was to determine mbl2 genotype frequencies in future solid organ transplant recipients in order to optimize their induction and maintenance immunosuppressive therapies, and to provide MBL reference data for this unique population. We genotyped 1687 patients, and concurrently measured protein in 807 of them, during 2010-2011. Frequencies of the structural allele SNPs in our population were similar to those of other studied populations; however, Black patients with the same intermediate and deficient mbl2 genotypes as Caucasians produced significantly lower levels of MBL protein; therefore, within this population more genotypes should be considered MBL-deficient. Overall, the most critical parameter in determining serum MBL protein concentration was genotype, which was independent of other factors including ethnicity, gender, or diseased native organ type.

Variation in PTX3 is associated with primary graft dysfunction after lung transplantation

RATIONALE

Elevated long pentraxin-3 (PTX3) levels are associated with the development of primary graft dysfunction (PGD) after lung transplantation. Abnormalities in innate immunity, mediated by PTX3 release, may play a role in PGD pathogenesis.

OBJECTIVES

Our goal was to test whether variants in the gene encoding PTX3 are risk factors for PGD.

METHODS

We performed a candidate gene association study in recipients from the multicenter, prospective Lung Transplant Outcomes Group cohort enrolled between July 2002 and July 2009. The primary outcome was International Society for Heart and Lung Transplantation grade 3 PGD within 72 hours of transplantation. Targeted genotyping of 10 haplotype-tagging PTX3 single-nucleotide polymorphisms (SNPs) was performed in lung transplant recipients. The association between PGD and each SNP was evaluated by logistic regression, adjusting for pretransplantation lung disease, cardiopulmonary bypass use, and population stratification. The association between SNPs and plasma PTX3 levels was tested across genotypes in a subset of recipients with idiopathic pulmonary fibrosis.

MEASUREMENTS AND MAIN RESULTS

Six hundred fifty-four lung transplant recipients were included. The incidence of PGD was 29%. Two linked 5' region variants, rs2120243 and rs2305619, were associated with PGD (odds ratio, 1.5; 95% confidence interval, 1.1 to 1.9; P = 0.006 and odds ratio, 1.4; 95% confidence interval, 1.1 to 1.9; P = 0.007, respectively). The minor allele of rs2305619 was significantly associated with higher plasma PTX3 levels measured pretransplantation (P = 0.014) and at 24 hours (P = 0.047) after transplantation in patients with idiopathic pulmonary fibrosis.

CONCLUSIONS

Genetic variants of PTX3 are associated with PGD after lung transplantation, and are associated with increased PTX3 plasma levels.

Lung-enriched organisms and aberrant bacterial and fungal respiratory microbiota after lung transplant

RATIONALE

Long-term survival after lung transplantation is limited by infectious complications and by bronchiolitis obliterans syndrome (BOS), a form of chronic rejection linked in part to microbial triggers.

OBJECTIVES

To define microbial populations in the respiratory tract of transplant patients comprehensively using unbiased high-density sequencing.

METHODS

Lung was sampled by bronchoalveolar lavage (BAL) and upper respiratory tract by oropharyngeal wash (OW). Bacterial 16S rDNA and fungal internal transcribed spacer sequencing was used to profile organisms present. Outlier analysis plots defining taxa enriched in lung relative to OW were used to identify bacteria enriched in lung against a background of oropharyngeal carryover.

MEASUREMENTS AND MAIN RESULTS

Lung transplant recipients had higher bacterial burden in BAL than control subjects, frequent appearance of dominant organisms, greater distance between communities in BAL and OW indicating more distinct populations, and decreased respiratory tract microbial richness and diversity. Fungal populations were typically dominated by Candida in both sites or by Aspergillus in BAL but not OW. 16S outlier analysis identified lung-enriched taxa indicating bacteria replicating in the lower respiratory tract. In some cases this confirmed respiratory cultures but in others revealed enrichment by anaerobic organisms or mixed outgrowth of upper respiratory flora and provided quantitative data on relative abundances of bacteria found by culture.

CONCLUSIONS

Respiratory tract microbial communities in lung transplant recipients differ in structure and composition from healthy subjects. Outlier analysis can identify specific bacteria replicating in lung. These findings provide novel approaches to address the relationship between microbial communities and transplant outcome and aid in assessing lung infections.

Increased plasma mannose binding lectin levels are associated with bronchiolitis obliterans after lung transplantation

Background

Long-term lung allograft survival is limited by bronchiolitis obliterans syndrome (BOS). Mannose binding lectin (MBL) belongs to the innate immune system, participates in complement activation, and may predispose to graft rejection. We investigated mannose binding (MBL) during cold ischemia and in tissue samples from explanted lungs with BOS, and assessed MBL and complement proteins in plasma post-lung transplantation relative to BOS staging.

Methods

MBL was detected by immunohistochemistry lung tissue at the time of cold ischemia and in samples with BOS. MBL was assayed in the peripheral blood of 66 lung transplant patients transplanted between 1990–2007.

Results

MBL localized to vasculature and basement membrane during cold ischemia and BOS. Patients further out post-lung transplant > 5 years (n = 33), had significantly lower levels of MBL in the blood compared to lung transplant patients < 5 years with BOS Op-3 (n = 17), 1738 ± 250 ng/ml vs 3198 ± 370 ng/ml, p = 0.027, and similar levels to lung transplant patients < 5 years with BOS 0 (n = 16), 1738 ± 250 ng/ml vs 1808 ± 345 ng/ml. MBL levels in all BOS 0 (n = 30) vs. all BOS Op-3 (n = 36) were 1378 ± 275 ng/ml vs. 2578 ± 390 ng/ml, p = 0.001, respectively. C3 plasma levels in BOS 0 (n = 30) vs. BOS Op-3 (n = 36) were 101 ± 19.8 mg/ml vs. 114 ± 25.2 mg/ml, p = 0.024, respectively.

Conclusions

MBL localizes within the lung during graft ischemia and BOS, higher levels of plasma MBL are associated with BOS Op-3 and < 5 years post-transplant, and higher level of plasma complement protein C3 was associated with BOS Op-3 clinical status. MBL may serve as a biomarker for poorer outcome post-lung transplantation.

Decreased efferocytosis and mannose binding lectin in the airway in bronchiolitis obliterans syndrome

BACKGROUND

Mannose binding lectin (MBL) is a key mediator of both innate immunity and efferocytosis (phagocytosis of apoptotic cells) in the airway. Defective efferocytosis results in a net increase in apoptotic material that can undergo secondary necrosis, leading to tissue damage and chronic inflammation. We have shown reduced MBL and efferocytosis in other chronic inflammatory lung diseases; we therefore hypothesized that reduced MBL and efferocytosis in the airways may be a determinant of bronchiolitis obliterans syndrome (BOS) after lung transplantation.

METHODS

We investigated MBL (enzyme-linked immunosorbent assay [ELISA]), MBL-mediated complement deposition (UC4, ELISA), and efferocytosis of apoptotic bronchial epithelial cells (flow cytometry) in bronchoalveolar lavage (BAL) and peripheral blood from 75 lung transplant recipients, comprising 16 with stable graft function, 34 stable with proven infection, 25 with BOS, and 14 healthy controls.

RESULTS

In plasma, MBL levels were highly variable (0-17.538 μg/ml), but increased in infected patients vs control (p = 0.09) or stable groups (p = 0.003). There was a similar increase in UC4 in infected patients and a significant correlation between MBL and UC4. There was no correlation between MBL and time after transplant. In BAL, MBL levels were less variable (0-73.3 ng/ml) and significantly reduced in patients with BOS vs controls and stable groups. Efferocytosis was significantly reduced in the BOS group vs control and stable groups (mean [SEM] control, 20% [1.3%]; stable, 20.5% [2.5%]; infected, 17.3% [2.8%]; BOS, 11.3% [1.5%], p = 0.04).

CONCLUSIONS

Low levels of MBL in the airway may play a role in reduced efferocytosis, subsequent tissue damage, and BOS after lung transplantation.

High levels of mannose-binding lectin are associated with poor outcomes after lung transplantation

BACKGROUND

Mannose-binding lectin (MBL) is a key molecule of the innate immune system and, in addition to the classical and alternative pathways, a principle driver of complement activation. Genetic mutations of MBL are common, result in low serum levels of MBL, and are associated with increased infection risk in solid-organ transplant recipients.

METHODS

We performed a retrospective study of MBL2 genotype and plasma and bronchoalveolar lavage (BAL) MBL levels in 37 lung transplant recipients (LTR). Plasma MBL levels were measured pretransplant and both plasma and BAL MBL levels were measured at 3, 6, and 12 months after lung transplantation. MBL2 genotyping was performed on recipient and donor peripheral blood mononuclear cells. Clinical variables analyzed included primary graft dysfunction, intensive care unit stay, acute allograft rejection, infection, bronchiolitis obliterans syndrome (BOS), and mortality.

RESULTS

Plasma MBL levels posttransplant were predicted by recipient, and not donor MBL2 genotype. Compared with pretransplant levels, plasma MBL was significantly increased at 3, 6, and 12 months posttransplant (P<0.05). LTR who developed BOS or died during the study period had higher plasma MBL levels at 6 and 12 months posttransplant (P ≤ 0.05) compared with LTR with stable graft function. MBL was not routinely detected in the lung allograft; however if present in the BAL at 3 and 6 months posttransplant, it was associated with the later development of BOS (P<0.05).

CONCLUSIONS

Plasma MBL levels increase after lung transplantation and persistently increased MBL levels are associated with poor long-term outcomes.

Mannose-binding lectin deficiency linked to cytomegalovirus (CMV) reactivation and survival in lung transplantation

Despite the use of immunosuppressives mainly influencing T and B cell responses, the prevalence of the bronchiolitis obliterans syndrome (BOS) after lung transplantation is high. Mannose-binding lectin (MBL) is a pattern recognition molecule of complement and an important component of the innate immunity. MBL is associated with rejection, infection and survival in other solid organ transplantations. In this study the relation between functional MBL levels and cytomegalovirus (CMV) reactivations and the development of BOS and survival after lung transplantation was investigated. MBL levels were measured in 85 patients before and in 57 of these patients after lung transplantation. The relation of MBL on survival, CMV reactivation and the development of BOS were investigated with Kaplan-Meier (log-rank) survival analysis. MBL levels decreased on average by 20% (P < 0·001) after transplantation and eventually returned to pretransplant levels. Fourteen of the 85 patients had deficient pretransplant MBL levels and these patients had a tendency towards a better survival compared to those with normal MBL levels (P = 0·08). Although no correlation was found between MBL deficiency and the development of BOS, more CMV reactivations occurred in recipients with deficient versus normal levels of MBL (P = 0·03). Our results suggest that MBL deficiency is associated with CMV reactivations and a longer overall survival, but not with the development of BOS.