Assistant Professor Children's Hosp. of Philadelphia, United States
Introduction/Rationale: Circadian rhythms provide an anticipatory system for the host to improve survival when facing threats. Relevant to acute infections, a hallmark of circadian control is that the host's response varies by the time of day at which the infection is sustained. We have previously shown that mice infected with Influenza A virus (IAV) at dawn had 3-fold better survival than those infected at dusk- this protection is lost with disruption of the clock. Further, we identified a unique role of Natural Killer (NK) cells, specifically the NK cell intrinsic clock in mediating this clock-driven protection from IAV.
Methods: Here we investigate how the NK cell clock protects against IAV, by using the Ncr1cre+ Bmal1fl/fl (Bmal1ΔNK) mice, wherein the clock is disrupted in only the NK cells. Bmal1ΔNK and their WT littermates were infected with IAV (PR8) and lungs harvested for flowcytometry, viral titration, ELISA for cytokines, and histological analyses, including Immunofluorescence staining. Further, we also sorted NK cells from the lungs of naive and flu-infected (day 4 post-infection) mice, and performed scRNA sequencing and analyses as well as sn-RNA-seq on day 8 p.i .
Results: Bmal1ΔNK lungs had more leukocytes but fewer NK cells in the uninfected state. After infection, Bmal1ΔNK had threefold higher mortality, worse immunopathology, and fewer NK cells than WT littermates, despite comparable viral titers. Single-cell RNA sequencing of sorted pulmonary NK cells from both Bmal1ΔNK and WT littermates revealed a role for IL-18 signaling in NK cell clock-driven protection from IAV. Neutralizing IL-18 signaling rescues the IAV-induced mortality in the Bmal1ΔNK mice. Further, Sn-RNAseq revealed a unique activation profile for CD8+ cells in the Bmal1ΔNK vs WT lungs, which is amplifies the effect of NK cell clock disruption.
Conclusion: In summary, the NK cell-intrinsic circadian clock protects against IAV by a controlled IL-18 signaling and optimizing CD8+ T cell responses.
