BACKGROUND: The 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. METHODS: We 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. RESULTS: Compared 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. CONCLUSION: BDG 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. FUNDING: University 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).

Background: Lung microbiota profiles in patients with early idiopathic pulmonary fibrosis (IPF) have been associated with disease progression; however, the topographic heterogeneity of lung microbiota and their roles in advanced IPF are unknown. Methods: We sampled subpleural tissue from up to three lobes as well as airway-based specimens (bronchial washings and airway tissue) in patients with IPF, connective tissue disease-associated interstitial lung disease (CTD-ILD), cystic fibrosis (CF), and chronic obstructive pulmonary disease (COPD) and donor lungs deemed unsuitable for transplant (controls). We quantified bacterial load and profiled communities by polymerase chain reaction (PCR) amplification and sequencing of the 16S rRNA gene. Findings: Explants from 62 IPF, 15 CTD-ILD, 20 CF, 20 COPD and 20 control patients were included. Airway-based samples had higher bacterial load compared to distal parenchymal tissue across all patient groups. IPF basilar tissue had much lower bacterial load compared to CF and control lungs (p<0.001). Among patients with IPF, no differences in microbial community profiles were found between parenchymal tissue samples from different lobes. With Dirichlet multinomial models, a cluster of IPF patients (29%) with distinct composition, high bacterial load and low alpha diversity was identified, exhibiting higher odds for acute exacerbation of IPF or death. Interpretation: IPF explants exhibited low biomass in the distal parenchyma of all three lobes with higher bacterial load in the airways. The discovery of a distinct subgroup of IPF patients with higher bacterial load and worse clinical outcomes supports investigation of personalized medicine approaches for microbiome-targeted interventions. Key Messages: What is the key question? Bronchoalveolar lavage microbiome profiles in early idiopathic pulmonary fibrosis (IPF) have been associated with disease progression, but the regional heterogeneity of resident microbiota in end-stage IPF has not been defined. What is the bottom line? IPF explants demonstrate higher bacterial load in airway compared to parenchymal samples, but no differences in between apical or basilar parenchymal samples. A subgroup of patients with higher bacterial load and respiratory pathogen abundance was associated with worse clinical outcomes. Why read on? Patient-specific heterogeneity in the lung microbiome of IPF supports the need for personalized microbiome-targeted interventions in IPF.

Background: The fungal cell-wall constituent (1,3)-β-d-glucan (BDG) is a pathogen-associated molecular pattern (PAMP) that can stimulate innate immunity. We hypothesized that BDG from colonizing fungi in critically-ill patients may translocate into the systemic circulation and thus be associated with host inflammatory responses and outcomes. Methods: We enrolled 453 mechanically-ventilated patients with acute respiratory failure with no evidence of invasive fungal infection (IFI). From serial plasma samples, we measured BDG, innate immunity and epithelial permeability biomarkers. From lower respiratory tract and stool samples we quantified bacterial and fungal DNA load using culture-independent techniques. Results: A positive BDG test (>60pg/ml) at baseline was detected in 19% of patients. BDG levels were significantly associated with markers of innate immunity (interleukin-6, tumor necrosis factor receptor-1 and procalcitonin), epithelial barrier disruption (receptor for advanced glycation end-products and fatty-acid binding protein-2, for lung and gut respectively) and with higher probability of classification in an adverse prognosis hyperinflammatory subphenotype (all p<0.05). No differences in fungal or bacterial DNA load were found by BDG test positivity. Positive BDG testing was associated with higher incidence of acute kidney injury, fewer ventilator free days and worse 30-day survival (adjusted p3 days from intubation) had higher mortality than patients with persistently negative test on follow-up (p<0.05). Conclusions: This is the first study to demonstrate the prognostic role of BDG in critically ill patients with no evidence of IFI. Translocation of BDG into systemic circulation may contribute to inflammation and clinical outcomes. Funding support: National Institutes of Health [K23 HL139987 (GDK); U01 HL098962 (AM); P01 HL114453 (BJM); R01 HL097376 (BJM); K24 HL123342 (AM); U01 HL137159 (DVM, PVB); R01 LM012087 (DVM, PVB); R01 HL142084 (JSL); R01 HL136143 (JSL); F32 HL137258 (JWE); F32 HL142172 (WB); K08 HS025455 (IJB); K23 GM122069 (FS)].