(406) IL-17A⁺ γδ T Cells Are Compromised by ICU-Associated Sleep Fragmentation, Increasing Pneumonia Susceptibility

Introduction/Rationale: Critically ill patients experience profound sleep disruption and are at high risk for bacterial pneumonia. Using a murine model of ICU-associated sleep fragmentation (ICU-SF) combined with Streptococcus pneumoniae (Sp) infection, we previously showed that ICU-SF impairs bacterial clearance and worsens lung injury. We hypothesized that ICU-SF increases pneumonia susceptibility by selectively compromising antibacterial immunity. To test this, we used our combined ICU-SF and Sp model to characterize pulmonary immune populations involved in host defense.

Methods: Wildtype mice were subjected to ICU-SF using an orbital shaker and infected with Sp. Control groups included mice exposed to neither ICU-SF nor Sp, Sp alone, or ICU-SF alone. Lungs were harvested, enzymatically digested into single-cell suspensions, stained for surface and intracellular markers, and analyzed by spectral flow cytometry (Sony ID7000). Data were analyzed using FlowJo v10 and Prism 10 (Mann-Whitney or Kruskal-Wallis tests; p< 0.05).

Results: ICU-SF alone led to a marked reduction in lung γδT cells with no change in macrophage or neutrophil numbers. ICU-SF also selectively decreased lung IL-17A+ γδT cells among IL-17A-producing lymphocytes. 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 infected 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: These findings identify a specific immune vulnerability induced by ICU-SF—IL-17A+ γδ T cell reduction—which may represent a key mechanism underlying increased susceptibility to hospital-acquired pneumonia in critically ill patients.