Objective:

The commentary presents findings from transcriptomic subphenotyping of the lungs in four cohorts of patients with severe pneumonia and discusses their potential implications for critical care.

Approach:

• Lung phenotyping: Transcriptomic analysis of bronchoalveolar lavage cells across four cohorts identified three pulmonary phenotypes, termed pneumotypes Pn1, Pn2, and Pn3.
• Comparison with blood: The pneumotypes were not detectable in blood. Blood transcriptomics identified two subphenotypes related to Sepsis Response Signatures, and lung and blood types interacted in predicting mortality.
• Validation: Single-cell datasets were used to validate findings related to distal alveolar stem cells in Pn2 and immature neutrophils in Pn3.

Key Findings:

• Pn1 was relatively hypoinflammatory, with low alveolar cytokines, sparse neutrophils, expanded alveolar macrophages, severe respiratory failure, and frequent alveolar haemorrhage. It was more common in immunosuppressed patients, although 44% of affected individuals were not immunosuppressed.
• Pn1 showed altered surfactant-processing gene expression. Proposed mechanisms involving lipid accumulation and epithelial injury remain unconfirmed.
• Pn2 had an intermediate immune profile and strong epithelial-repair and stem-cell signatures. It was associated with faster ventilator liberation and the lowest mortality.
• Pn3 featured elevated cytokines, substantial neutrophil and monocyte infiltration, and signatures of immature neutrophils. The authors suggest that self-reinforcing inflammatory cycles may help explain persistent lung injury after pathogen clearance.
• Pneumotype and blood subphenotype interacted in predicting mortality. The poorest outcomes occurred in patients with the least pulmonary inflammation and the more inflammatory blood signature.

Interpretation:

The authors report that pulmonary pneumotypes were not detectable in blood, while blood transcriptomics identified two subphenotypes related to Sepsis Response Signatures. They propose that the distinct pulmonary patterns may help explain variation in lung injury, repair, and outcomes; the mechanisms proposed for Pn1 and Pn3 remain unconfirmed.

Limitations:

• The proposed mechanisms involving altered surfactant processing in Pn1 and persistent inflammatory cycles in Pn3 require further investigation.

Conclusion:

The commentary describes three pulmonary pneumotypes in severe pneumonia, with distinct immune features and associations with clinical outcomes. The authors state that the proposed biological mechanisms require further investigation.

Sources:

• Article context provided by the user