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

Klebsiella pneumoniae, a common cause of severe and antibiotic-resistant pneumonia, poses a significant public health concern. Follistatin-like 1 (FSTL-1) is a protein with diverse roles in lung development, homeostasis, tissue remodeling, and inflammation, but its function in fighting bacterial infections is unclear. Researchers have discovered that FSTL-1 levels increase in the lungs of humans and mice during bacterial pneumonia.

To investigate FSTL-1's role, scientists created a special mouse model lacking the FSTL-1 gene. This knockout mouse model showed that FSTL-1 is essential for clearing bacteria from the lungs and recruiting neutrophils, immune cells that fight infections. When the scientists introduced recombinant FSTL-1 into the knockout mice, it restored the mice's ability to fight off the K. pneumoniae infection.

The researchers found that FSTL-1's protective effect depended on neutrophils and two other proteins, Cd14 and Nr4a1, that are involved in a specific lung immune response. These findings reveal FSTL-1 as a critical factor in the immune system's ability to clear bacteria from the lungs, opening up new possibilities for treating bacterial pneumonia infections.