Functional differences in lung neutrophil subpopulations identified by flow cytometry during acute Streptococcus pneumoniae infection in mice

Neutrophils are rapidly recruited into the lungs after Spn infection, where they eliminate the bacterium while eliciting inflammation. During Spn infection, two neutrophil subpopulations differing in size (FSClow and FSChigh) have been described, but their biological implications remain unknown.

Here we evaluated the appearance kinetics of these subpopulations in the lungs during Spn infection in vivo, observing a significant increase in total neutrophils at 12 and 24 hours post-infection (hpi) with a reduction of the FSChigh population relative to uninfected mice. By flow cytometry, FSClow neutrophils showed higher affinity for DAPI and lower expression of Ly6G and CD44 than FSChigh neutrophils, suggesting a subpopulation undergoing cell death.