A single dose of β-glucan “trains” lung immune cells via IFN-γ and neutrophils and makes later lung injury worse in mice.

Objective
Assess whether systemic β-glucan induces trained immunity in the lung by reprogramming alveolar macrophages (AMs), define the upstream requirements (neutrophils, IFNγ, Dectin-1, type I IFN), and determine its functional impact on acute lung injury (ALI) triggered by bacterial (LPS/TLR4) or viral (poly(I:C)/TLR3) stimuli.

Methods

• C57BL/6 mice received β-1,3-glucan (Saccharomyces cerevisiae) 1 mg i.p. once; ALI was induced intranasally 7 or 28 days later with LPS (50 µg) or poly(I:C) (50 µg). 
• Lung injury was quantified by micro-CT (non-aerated fraction, Hounsfield units), Evans blue permeability, BAL protein, histology, and BAL cytokines/chemokines. 
• Cellular readouts included BAL neutrophils and AM counts/phenotype. AMs were depleted with intranasal clodronate; AM-deficient Csf2rb−/− mice and AM adoptive transfer tested necessity/sufficiency. 
• Bulk RNA-seq and Seahorse assays characterized AM transcriptional and metabolic programs ex vivo with/without LPS. 
• Mechanistic requirements were probed in Clec7a−/− (Dectin-1), Ifnar−/− (type I IFN), and IfngR−/− (IFNγR) mice, and by depleting neutrophils (anti-Ly6G) or IFNγ (neutralizing antibody) around the β-glucan dose.

Results

• β-Glucan exacerbated ALI. Trained mice displayed greater non-aerated lung on micro-CT, higher Evans blue leakage, and worse histology after LPS; weight recovery lagged. Effects persisted at 28 days and recapitulated with poly(I:C).
• Neutrophilic inflammation increased. BAL neutrophils approximately doubled post-challenge, with higher CXCL1, IL-6, and TNF (TNF not increased in poly(I:C) model). AM numbers were unchanged, but CD80 frequency rose.
• AMs mediate the phenotype. AM depletion or genetic absence (Csf2rb−/−) abrogated β-glucan-augmented ALI; transferring AMs from trained donors restored heightened inflammation and permeability in AM-deficient recipients.
• Reprogrammed AM responses. RNA-seq and protein readouts showed β-glucan-trained AMs mounted amplified LPS-induced expression/production of IL-6, IL-1, TNF, CXCL1, with metabolic rewiring (increased  mitochondrial respiration; upon LPS, increased  respiration and glycolysis).

Upstream requirements. Training of AMs and augmented ALI were independent of Dectin-1 and type I IFN but dependent on IFNγ signaling (lost in IfngR−/− mice). Early after β-glucan, BAL IFNγ and neutrophils rose; depleting IFNγ or neutrophils during training blunted the AM hyper-responsiveness.

Interpretation
A single systemic β-glucan dose induces peripheral trained immunity in the lung by reprogramming AMs. This state is neutrophil/IFNγ-dependent and heightens downstream responses to bacterial and viral mimetics, worsening ALI despite unchanged AM numbers. Mechanistically, β-glucan establishes a poised transcriptional/metabolic AM program that over-produces chemokines/cytokines upon restimulation.

Mechanisms & pathways

• Axis: β-glucan promotes early neutrophil influx which increased IFNγ and trained AM resulting in amplified LPS/poly(I:C) responses.
• Receptors/signals: Dectin-1-independent; type I IFN-independent; IFNγR-dependent.
• Cellular programs: Enhanced CXCL1/IL-6/TNF; metabolic shift (increased OXPHOS; LPS-triggered increased glycolysis); stable AM pool with increased activation marker (CD80).

Dosages & adverse reactions

• β-1,3-glucan 1 mg i.p. once; challenge at day 7 or 28.
• LPS or poly(I:C) 50 µg intranasal.
• Adverse effects are preclinical and mechanistic: β-glucan priming increased lung permeability/inflammation and delayed weight recovery post-LPS; no formal toxicology beyond these disease-model readouts.

Quality of study (assessment)

• Strengths: Multi-model validation (LPS and poly(I:C)), durability to 28 days; necessity/sufficiency demonstrated by AM depletion and adoptive transfer; genetic dissection (Clec7a−/−, Ifnar−/−, IfngR−/−); integrated transcriptomic and metabolic profiling; blinded histology scoring.
• Limitations: Murine study; single β-glucan source/dose/route; mechanism upstream of IFNγ source unresolved; data collection/analysis not uniformly blinded; some complex experiments performed once; no systemic safety panel or infection outcomes.

Implications
β-Glucan–based “innate training” can be context-dependent and detrimental in sterile or viral lung inflammation by amplifying AM-driven neutrophilic injury. In clinical settings with high IFNγ tone or anticipated ALI (e.g., sepsis, viral pneumonitis), β-glucan exposure could theoretically exacerbate immunopathology; conversely, targeting the neutrophil/IFNγ–AM axis may mitigate lung injury. Translation will require human dosing, kinetics, formulation comparisons, and rigorous safety assessment.