A14-03 Intensive Care Unit-Associated Sleep Fragmentation Impairs the Gamma Delta T Cell-Interleukin-17A Axis Promoting Pneumonia Susceptibility

Rationale 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). Results 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 interleukin-17A (IL-17A)+ γδT cells among 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. Conclusion 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 in the γδT cell-IL-17A axis may represent a key mechanism contributing to the heightened risk of hospital-acquired pneumonia in ICU patients.