Rapid regulation of plasmacytoid dendritic cells after gravitational changes in parabolic flight

<title>Abstract</title> <p> Spaceflight-associated gravitational stress can impair immune surveillance and increase infection susceptibility during crewed missions. However, early effects on rare immune cell populations and their regulatory mediators remain poorly defined. <bold/> Here, we investigated acute immune alterations in healthy individuals exposed to parabolic flight as a model of rapid gravitational changes. Peripheral blood mononuclear cells and plasma were collected before, 1 h after, and 24 h after parabolic flight. Deep cellular phenotyping was performed by cytometry by time-of-flight (CyTOF), and plasma proteins were quantified using proximity extension assays (PEA). Parabolic flight modulated immune-trafficking mediators including CXCL12 and CCL21. A rapid reduction of circulating plasmacytoid dendritic cells (pDCs) correlated with the drop of CCL21 and was accompanied by distinct changes in T cell subsets. In conclusion, reduced CXCL12 and CCL21 could contribute to altered pDC mobilization. These findings identify pDCs as gravity-sensitive cells and suggest impaired antiviral immune surveillance after acute gravitational stress. </p>