Intensive care unit-associated sleep fragmentation impairs pulmonary innate immunity increasing susceptibility to pneumonia

STUDY OBJECTIVE: To determine how ICU-associated sleep fragmentation alters pulmonary immune responses to S. pneumoniae, with a specific focus on whether it impairs antibacterial host defense by reducing IL-17A–producing γδT cells. HYPOTHESIS: Critically ill patients experience profound sleep disruption and are at high risk for developing bacterial pneumonia. Using a murine model of ICU-associated sleep fragmentation (ICU-SF) combined with S. pneumoniae pneumonia, we previously showed that ICU-SF impairs bacterial clearance and exacerbates lung injury, suggesting increased susceptibility to pneumonia. We hypothesize that ICU-SF predisposes to bacterial pneumonia by compromising antibacterial immunity. To test this, we applied our murine model of combined ICU-SF and S. pneumoniae to characterize pulmonary immune cells involved in bacterial host defense. METHODS: Wildtype mice were subjected to ICU-SF using an orbital shaker and infected with S. pneumoniae (Sp). Control groups included: neither ICU-SF nor Sp, Sp alone, and ICU-SF alone. Lungs were then harvested and enzymatically digested into single cell suspensions. Cells were stained for surface markers and intracellular targets and analyzed on a Sony ID7000 Spectral Cell Analyzer. Data were processed in FlowJo v10 and analyzed by Mann-Whitney test or Kruskal-Wallis test (Prism 10, p< 0.05). DATA & RESULTS SUMMARY: ICU-SF alone led to a marked reduction in pulmonary γδT cells with no change in the number of macrophages or neutrophils. Additionally, ICU-SF selectively decreased lung IL-17A+ γδT cells among all lymphocytes capable of producing IL-17A. Given the vital role of early IL-17A in bacterial clearance and prevention of pneumonia, we tested whether these findings persisted in the presence of Sp. In response to infection, we found a significant increase in pulmonary IL-17A+ γδT cells compared to uninfected controls. However, infected mice exposed to ICU-SF showed significantly decreased numbers of IL-17A+ γδT cells compared to non-ICU-SF controls. There was no difference in the number of IL-17A-producing CD4+ T cells, CD8+ T cells, group 3 innate lymphoid cells, or natural killer cells. CONCLUSIONS: Our findings suggest that ICU-SF engenders a specific locus of immune vulnerability to bacterial pneumonia: a reduction in IL-17A+ γδT cells. This deficit may represent a key mechanism contributing to the heightened risk of hospital-acquired pneumonia in ICU patients. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.