Dectin-1 genetic deficiency predicts chronic lung allograft dysfunction and death

Genetic variants of dectin-1 and their antifungal immunity impact in hematologic malignancies: A comprehensive systematic review

BACKGROUND

Fungal infections pose a significant threat to individuals with hematologic malignancies due to compromised immune systems. Dectin-1, a pivotal pattern recognition receptor, plays a central role in antifungal immune responses. Understanding its genetic variants' impact is crucial for advancing personalized therapeutic approaches.

METHODS

Employing systematic review methods, studies were meticulously selected and assessed for relevance. Data extraction encompassed Dectin-1 genetic variants, antifungal immune responses, and disease outcomes.

RESULTS

Findings unveiled a complex relationship between Dectin-1 genetic variants and antifungal immunity in hematologic malignancies. Variable associations emerged, influencing susceptibility to fungal infections and disease prognosis. Moreover, implications for treatment outcomes were explored, suggesting potential avenues for tailored interventions.

CONCLUSIONS

This systematic review underscores the need for further investigation into the precise influence of Dectin-1 genetic variants on antifungal immunity and disease progression in hematologic malignancies. Insights gained could pave the way for personalized therapeutic strategies, optimizing infection prevention and malignancy management. By delving into the intricate connections between genetic nuances, immune responses, and clinical trajectories, this review contributes to the ongoing discourse surrounding hematologic malignancies, fungal infections, and their multifaceted interplay.

Impaired complement regulation drives chronic lung allograft dysfunction after lung transplantation

A greater understanding of chronic lung allograft dysfunction (CLAD) pathobiology, the primary cause of mortality after lung transplantation, is needed to improve outcomes. The complement system links innate to adaptive immune responses and is activated early post-lung transplantation to form the C3 convertase, a critical enzyme that cleaves the central complement component C3. We hypothesized that LTx recipients with a genetic predisposition to enhanced complement activation have worse CLAD-free survival mediated through increased adaptive alloimmunity. We interrogated a known functional C3 polymorphism (C3R102G) that increases complement activation through impaired C3 convertase inactivation in two independent LTx recipient cohorts. C3R102G, identified in at least one out of three LTx recipients, was associated with worse CLAD-free survival, particularly in the subset of recipients who developed donor-specific antibodies (DSA). In a mouse orthotopic lung transplantation model, impaired recipient complement regulation resulted in more severe obstructive airway lesions when compared to wildtype controls, despite only moderate differences in graft-infiltrating effector T cells. Impaired complement regulation promoted the intragraft accumulation of memory B cells and antibody-secreting cells, resulting in increased DSA levels. In summary, genetic predisposition to complement activation is associated with B cell activation and worse CLAD-free survival.

MICB Genomic Variant Is Associated with NKG2D-mediated Acute Lung Injury and Death

Rationale: Acute lung injury (ALI) carries a high risk of mortality but has no established pharmacologic therapy. We previously found that experimental ALI occurs through natural killer (NK) cell NKG2D receptor activation and that the cognate human ligand, MICB, was associated with ALI after transplantation. Objectives: To investigate the association of a common missense variant, MICBG406A, with ALI. Methods: We assessed MICBG406A genotypes within two multicenter observational study cohorts at risk for ALI: primary graft dysfunction (N = 619) and acute respiratory distress syndrome (N = 1,376). Variant protein functional effects were determined in cultured and ex vivo human samples. Measurements and Main Results: Recipients of MICBG406A-homozygous allografts had an 11.1% absolute risk reduction (95% confidence interval [CI], 3.2-19.4%) for severe primary graft dysfunction after lung transplantation and reduced risk for allograft failure (hazard ratio, 0.36; 95% CI, 0.13-0.98). In participants with sepsis, we observed 39% reduced odds of moderately or severely impaired oxygenation among MICBG406A-homozygous individuals (95% CI, 0.43-0.86). BAL NK cells were less frequent and less mature in participants with MICBG406A. Expression of missense variant protein MICBD136N in cultured cells resulted in reduced surface MICB and reduced NKG2D ligation relative to wild-type MICB. Coculture of variant MICBD136N cells with NK cells resulted in less NKG2D activation and less susceptibility to NK cell killing relative to the wild-type cells. Conclusions: These data support a role for MICB signaling through the NKG2D receptor in mediating ALI, suggesting a novel therapeutic approach.

Frailty and genetic risk predict fracture after lung transplantation

Fractures negatively impact quality of life and survival. We hypothesized that recipient frailty score and genetic profile measured before transplant would predict risk of fracture after lung transplant. We conducted a retrospective cohort study of bone mineral density (BMD) and fracture among lung transplant recipients at a single center. The association between predictors and outcomes were assessed by multivariable time-dependent Cox models or regression analysis. Among the 284 participants, osteoporosis and fracture were highly prevalent. Approximately 59% of participants had posttransplant osteopenia, and 35% of participants developed at least 1 fracture. Low BMD was associated with a polygenic osteoporosis risk score, and the interaction between genetic score and BMD predicted fracture. Pretransplant frailty was associated with risk for spine and hip fracture, which were not associated with chronic lung allograft dysfunction or death. Chest fractures were the most frequent type of fracture and conferred a 2.2-fold increased risk of chronic lung allograft dysfunction or death (time-dependent P < .001). Pneumonia, pleural effusions, and acute rejection frequently occurred surrounding chest fracture. Pretransplant frailty and recipient genotype may aid clinical risk stratification for fracture after transplant. Fracture carries significant morbidity, underscoring the importance of surveillance and osteoporosis prevention.

CD16+ natural killer cells in bronchoalveolar lavage are associated with antibody-mediated rejection and chronic lung allograft dysfunction

Acute and chronic rejections limit the long-term survival after lung transplant. Pulmonary antibody-mediated rejection (AMR) is an incompletely understood driver of long-term outcomes characterized by donor-specific antibodies (DSAs), innate immune infiltration, and evidence of complement activation. Natural killer (NK) cells may recognize DSAs via the CD16 receptor, but this complement-independent mechanism of injury has not been explored in pulmonary AMR. CD16⁺ NK cells were quantified in 508 prospectively collected bronchoalveolar lavage fluid samples from 195 lung transplant recipients. Associations between CD16⁺ NK cells and human leukocyte antigen mismatches, DSAs, and AMR grade were assessed by linear models adjusted for participant characteristics and repeat measures. Cox proportional hazards models were used to assess CD16⁺ NK cell association with chronic lung allograft dysfunction and survival. Bronchoalveolar lavage fluid CD16⁺ NK cell frequency was associated with increasing human leukocyte antigens mismatches and increased AMR grade. Although NK frequencies were similar between DSA+ and DSA- recipients, CD16⁺ NK cell frequencies were greater in recipients with AMR and those with concomitant allograft dysfunction. CD16⁺ NK cells were associated with long-term graft dysfunction after AMR and decreased chronic lung allograft dysfunction-free survival. These data support the role of CD16⁺ NK cells in pulmonary AMR.

NKG2D receptor activation drives primary graft dysfunction severity and poor lung transplantation outcomes

Clinical outcomes after lung transplantation, a life-saving therapy for patients with end-stage lung diseases, are limited by primary graft dysfunction (PGD). PGD is an early form of acute lung injury with no specific pharmacologic therapies. Here, we present a large multicenter study of plasma and bronchoalveolar lavage (BAL) samples collected on the first posttransplant day, a critical time for investigations of immune pathways related to PGD. We demonstrated that ligands for NKG2D receptors were increased in the BAL from participants who developed severe PGD and were associated with increased time to extubation, prolonged intensive care unit length of stay, and poor peak lung function. Neutrophil extracellular traps (NETs) were increased in PGD and correlated with BAL TNF-α and IFN-γ cytokines. Mechanistically, we found that airway epithelial cell NKG2D ligands were increased following hypoxic challenge. NK cell killing of hypoxic airway epithelial cells was abrogated with NKG2D receptor blockade, and TNF-α and IFN-γ provoked neutrophils to release NETs in culture. These data support an aberrant NK cell/neutrophil axis in human PGD pathogenesis. Early measurement of stress ligands and blockade of the NKG2D receptor hold promise for risk stratification and management of PGD.

Candida Administration in 5/6 Nephrectomized Mice Enhanced Fibrosis in Internal Organs: An Impact of Lipopolysaccharide and (1→3)-β-D-Glucan from Leaky Gut

Uremic toxins and gut dysbiosis in advanced chronic kidney disease (CKD) can induce gut leakage, causing the translocation of gut microbial molecules into the systemic circulation. Lipopolysaccharide (LPS) and (1→3)-β-D-glucan (BG) are the major gut microbial molecules of Gram-negative bacteria and fungi, respectively, and can induce inflammation in several organs. Here, the fibrosis in the kidney, liver, and heart was investigated in oral C. albicans-administered 5/6 nephrectomized (Candida-5/6 Nx) mice. At 20 weeks post 5/6 Nx, Candida-5/6 Nx mice demonstrated increased 24 h proteinuria, liver enzymes, and serum cytokines (TNF-α, IL-6, and IL-10), but not weight loss, systolic blood pressure, hematocrit, serum creatinine, or gut-derived uremic toxins (TMAO and indoxyl sulfate), compared to in 5/6 Nx alone. The gut leakage in Candida-5/6 Nx was more severe, as indicated by FITC-dextran assay, endotoxemia, and serum BG. The areas of fibrosis from histopathology, along with the upregulated gene expression of Toll-like receptor 4 (TLR-4) and Dectin-1, the receptors for LPS and BG, respectively, were higher in the kidney, liver, and heart. In vitro, LPS combined with BG increased the supernatant IL-6 and TNF-α, upregulated the genes of pro-inflammation and pro-fibrotic processes, Dectin-1, and TLR-4 in renal tubular (HK-2) cells and hepatocytes (HepG2), when compared with LPS or BG alone. This supported the pro-inflammation-induced fibrosis and the possible LPS-BG additive effects on kidney and liver fibrosis. In conclusion, uremia-induced leaky gut causes the translocation of gut LPS and BG into circulation, which activates the pro-inflammatory and pro-fibrotic pathways, causing internal organ fibrosis. Our results support the crosstalk among several organs in CKD through a leaky gut.

Immunogenetics associated with severe coccidioidomycosis

Disseminated coccidioidomycosis (DCM) is caused by Coccidioides, pathogenic fungi endemic to the southwestern United States and Mexico. Illness occurs in approximately 30% of those infected, less than 1% of whom develop disseminated disease. To address why some individuals allow dissemination, we enrolled patients with DCM and performed whole-exome sequencing. In an exploratory set of 67 patients with DCM, 2 had haploinsufficient STAT3 mutations, and defects in β-glucan sensing and response were seen in 34 of 67 cases. Damaging CLEC7A and PLCG2 variants were associated with impaired production of β-glucan-stimulated TNF-α from PBMCs compared with healthy controls. Using ancestry-matched controls, damaging CLEC7A and PLCG2 variants were overrepresented in DCM, including CLEC7A Y238* and PLCG2 R268W. A validation cohort of 111 patients with DCM confirmed the PLCG2 R268W, CLEC7A I223S, and CLEC7A Y238* variants. Stimulation with a DECTIN-1 agonist induced DUOX1/DUOXA1-derived hydrogen peroxide [H2O2] in transfected cells. Heterozygous DUOX1 or DUOXA1 variants that impaired H2O2 production were overrepresented in discovery and validation cohorts. Patients with DCM have impaired β-glucan sensing or response affecting TNF-α and H2O2 production. Impaired Coccidioides recognition and decreased cellular response are associated with disseminated coccidioidomycosis.

Immune processes in the pathogenesis of chronic lung allograft dysfunction: identifying the missing pieces of the puzzle

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.

Depressive symptoms in lung transplant recipients: trajectory and association with mortality and allograft dysfunction

OBJECTIVE

Most studies observing an association between depressive symptoms following lung transplantation and mortality are limited to depressive symptom measurement at a single time point, unrelated to allograft function. We aimed to test the association of depressive symptoms over multiple assessments with allograft dysfunction and with mortality.

METHODS

We assessed depressive symptoms before and serially up to 3 years after lung transplantation in lung transplant recipients. We quantified depressive symptoms with the Geriatric Depression Scale (GDS; range 0-15; minimally important difference (MID): 2). We quantified changes in GDS using linear mixed effects models and tested the association with mortality using Cox proportional hazards models with GDS as a time-dependent predictor. To determine if worsening in GDS preceded declines in lung function, we tested the association of GDS as a time-dependent predictor with the lagged outcome of FEV₁ at the following study visit.

RESULTS

Among 266 participants, depressive symptoms improved early after transplantation. Worsening in post-transplant GDS by the MID was associated with mortality (HR 1.25, 95% CI 1.05 to 1.50), and in lagged outcome analyses with decreased per cent predicted FEV₁ (Δ, -1.62%, 95% CI -2.49 to -0.76). Visual analyses of temporal changes in GDS demonstrated that worsening depressive symptoms could precede chronic lung allograft dysfunction.

CONCLUSIONS

Depressive symptoms generally improve after lung transplantation. When they worsen, however, there is an association with declines in lung function and mortality. Depression is one of the few, potentially modifiable, risk factors for chronic lung allograft dysfunction and death.

Lymphocytic Airway Inflammation in Lung Allografts

Lung transplant remains a key therapeutic option for patients with end stage lung disease but short- and long-term survival lag other solid organ transplants. Early ischemia-reperfusion injury in the form of primary graft dysfunction (PGD) and acute cellular rejection are risk factors for chronic lung allograft dysfunction (CLAD), a syndrome of airway and parenchymal fibrosis that is the major barrier to long term survival. An increasing body of research suggests lymphocytic airway inflammation plays a significant role in these important clinical syndromes. Cytotoxic T cells are observed in airway rejection, and transcriptional analysis of airways reveal common cytotoxic gene patterns across solid organ transplant rejection. Natural killer (NK) cells have also been implicated in the early allograft damage response to PGD, acute rejection, cytomegalovirus, and CLAD. This review will examine the roles of lymphocytic airway inflammation across the lifespan of the allograft, including: 1) The contribution of innate lymphocytes to PGD and the impact of PGD on the adaptive immune response. 2) Acute cellular rejection pathologies and the limitations in identifying airway inflammation by transbronchial biopsy. 3) Potentiators of airway inflammation and heterologous immunity, such as respiratory infections, aspiration, and the airway microbiome. 4) Airway contributions to CLAD pathogenesis, including epithelial to mesenchymal transition (EMT), club cell loss, and the evolution from constrictive bronchiolitis to parenchymal fibrosis. 5) Protective mechanisms of fibrosis involving regulatory T cells. In summary, this review will examine our current understanding of the complex interplay between the transplanted airway epithelium, lymphocytic airway infiltration, and rejection pathologies.

Chronic Lung Allograft Dysfunction

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.

Human distal airways contain a multipotent secretory cell that can regenerate alveoli

The human lung differs substantially from its mouse counterpart, resulting in a distinct distal airway architecture affected by disease pathology in chronic obstructive pulmonary disease. In humans, the distal branches of the airway interweave with the alveolar gas-exchange niche, forming an anatomical structure known as the respiratory bronchioles. Owing to the lack of a counterpart in mouse, the cellular and molecular mechanisms that govern respiratory bronchioles in the human lung remain uncharacterized. Here we show that human respiratory bronchioles contain a unique secretory cell population that is distinct from cells in larger proximal airways. Organoid modelling reveals that these respiratory airway secretory (RAS) cells act as unidirectional progenitors for alveolar type 2 cells, which are essential for maintaining and regenerating the alveolar niche. RAS cell lineage differentiation into alveolar type 2 cells is regulated by Notch and Wnt signalling. In chronic obstructive pulmonary disease, RAS cells are altered transcriptionally, corresponding to abnormal alveolar type 2 cell states, which are associated with smoking exposure in both humans and ferrets. These data identify a distinct progenitor in a region of the human lung that is not found in mouse that has a critical role in maintaining the gas-exchange compartment and is altered in chronic lung disease.

Markers of rejection of a lung allograft: state of the art

Chronic lung allograft dysfunction (CLAD) affects approximately 50% of all lung transplant recipients by 5 post-operative years and is the leading cause of death in lung transplant recipients. Early CLAD diagnosis or ideally prediction of CLAD is essential to enable early intervention before significant lung injury occurs. New technologies have emerged to facilitate biomarker discovery, including epigenetic modification and single-cell RNA sequencing. This review examines new and existing technologies for biomarker discovery and the current state of research on biomarkers for identifying lung transplant rejection.

Emerging roles of Dectin-1 in noninfectious settings and in the CNS

Dectin-1 is a C-type lectin receptor (CLR) expressed on the surface of various mammalian myeloid cells. Dectin-1 recognizes β-glucans and elicits antifungal proinflammatory immune responses. Recent studies have begun to examine the biology of Dectin-1 in previously less explored settings, such as homeostasis, sterile inflammation, and in the central nervous system. Indeed, in certain contexts, Dectin-1 is now known to promote tolerance, and anti-inflammatory and neuroprotective responses. In this review, we provide an overview of the current understanding of the roles of Dectin-1 in immunology beyond the context of fungal infections, mainly focusing on in vivo neuroimmunology studies, which could reveal new therapeutic approaches to modify innate immune responses in neurologic disorders.

Plasma 1,3-β-d-glucan levels predict adverse clinical outcomes in critical illness

BACKGROUNDThe fungal cell wall constituent 1,3-β-d-glucan (BDG) is a pathogen-associated molecular pattern that can stimulate innate immunity. We hypothesized that BDG from colonizing fungi in critically ill patients may translocate into the systemic circulation and be associated with host inflammation and outcomes.METHODSWe enrolled 453 mechanically ventilated patients with acute respiratory failure (ARF) without invasive fungal infection and measured BDG, innate immunity, and epithelial permeability biomarkers in serially collected plasma samples.RESULTSCompared with healthy controls, patients with ARF had significantly higher BDG levels (median [IQR], 26 pg/mL [15-49 pg/mL], P < 0.001), whereas patients with ARF with high BDG levels (≥40 pg/mL, 31%) had higher odds for assignment to the prognostically adverse hyperinflammatory subphenotype (OR [CI], 2.88 [1.83-4.54], P < 0.001). Baseline BDG levels were predictive of fewer ventilator-free days and worse 30-day survival (adjusted P < 0.05). Integrative analyses of fungal colonization and epithelial barrier disruption suggested that BDG may translocate from either the lung or gut compartment. We validated the associations between plasma BDG and host inflammatory responses in 97 hospitalized patients with COVID-19.CONCLUSIONBDG measurements offered prognostic information in critically ill patients without fungal infections. Further research in the mechanisms of translocation and innate immunity recognition and stimulation may offer new therapeutic opportunities in critical illness.FUNDINGUniversity of Pittsburgh Clinical and Translational Science Institute, COVID-19 Pilot Award and NIH grants (K23 HL139987, U01 HL098962, P01 HL114453, R01 HL097376, K24 HL123342, U01 HL137159, R01 LM012087, K08HK144820, F32 HL142172, K23 GM122069).

Impacts of single nucleotide polymorphisms in Fc gamma receptor IIA (rs1801274) on lung transplant outcomes among Japanese lung transplant recipients

This study aimed to analyze the influences of single nucleotide polymorphisms (SNPs) in Fc gamma receptor IIA (FCGR2A) on postoperative outcomes after lung transplantation (LTx). We enrolled 191 lung transplant recipients (80 undergoing living-donor lobar lung transplants [LDLLTs] and 111 undergoing deceased-donor lung transplants [DDLTs]) in this study. We identified SNPs in FCGR2A (131 histidine [H] or arginine [R]; rs1801274) and reviewed the infectious complication-free survival after ICU discharge. The SNPs in FCGR2A comprised H/H (n=53), H/R (n=24), and R/R (n=3) in LDLLT, and H/H (n=67), H/R (n=42), and R/R (n=2) in DDLT. Recipients with H/H (H/H group) and those with H/R or R/R (R group) were compared in the analyses of infectious complications. In multivariate analyses, the R group of SNPs in FCGR2A was associated with pneumonia-free survival (HR: 2.52 [95% confidence interval {CI}: 1.35-4.71], p=0.004), fungal infection-free survival (HR: 2.50 [95% CI: 1.07-5.84], p=0.035), and cytomegalovirus infection-free survival (HR: 2.24 [95% CI: 1.07-4.69], p=0.032) in LDLLT but it was not associated with infectious complication-free survival in DDLT. Therefore, in LDLLT, more attention to infectious complications might need to be paid for LTx recipients with H/R or R/R than for those with H/H.

Complement activation on endothelium initiates antibody-mediated acute lung injury

Antibodies targeting human leukocyte antigen (HLA)/major histocompatibility complex (MHC) proteins limit successful transplantation and transfusion, and their presence in blood products can cause lethal transfusion-related acute lung injury (TRALI). It is unclear which cell types are bound by these anti-leukocyte antibodies to initiate an immunologic cascade resulting in lung injury. We therefore conditionally removed MHC class I (MHC I) from likely cellular targets in antibody-mediated lung injury. Only the removal of endothelial MHC I reduced lung injury and mortality, related mechanistically to absent endothelial complement fixation and lung platelet retention. Restoration of endothelial MHC I rendered MHC I-deficient mice susceptible to lung injury. Neutrophil responses, including neutrophil extracellular trap (NET) release, were intact in endothelial MHC I-deficient mice, whereas complement depletion reduced both lung injury and NETs. Human pulmonary endothelial cells showed high HLA class I expression, and posttransfusion complement activation was increased in clinical TRALI. These results indicate that the critical source of antigen for anti-leukocyte antibodies is in fact the endothelium, which reframes our understanding of TRALI as a rapid-onset vasculitis. Inhibition of complement activation may have multiple beneficial effects of reducing endothelial injury, platelet retention, and NET release in conditions where antibodies trigger these pathogenic responses.