Follistatin-like 1 Promotes Neutrophil-mediated Host Defense against Klebsiella pneumoniae

Follistatin-like 1 (FSTL-1) is elevated in lungs during Klebsiella pneumoniae pneumonia and is required for pulmonary bacterial clearance and neutrophil recruitment in mice.

• Why it matters: Antibacterial immunity in the lung depends on coordinated neutrophil responses, but how FSTL-1 contributes to host defense against K. pneumoniae is unclear.
• What they did: The study used an inducible Fstl1 knockout mouse model and tested whether recombinant FSTL-1 could rescue susceptibility, including conditions with neutrophil depletion and Cd14- or Nr4a1 deficiency.
• The result: FSTL-1–dependent protection was lost with neutrophil depletion and in Cd14-deficient or Nr4a1-deficient mice, identifying an FSTL-1/CD14/NR4A1-linked pathway that licenses neutrophil-mediated defense.

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