Spaceflight alters the immune regulatory functions of neutrophil granulocytes on T lymphocytes.

Spaceflight leads to dysregulation in the immune system. This study reports that neutrophils from astronauts undergo functional alterations and modulate T cell responses after spaceflight, analyzing samples from astronauts on an 18-day orbital mission (axiom mission 3, Ax-3) and a short suborbital flight. Normal-density neutrophils (NDN) and low-density neutrophils (LDN) were collected before and after the missions. Following the spaceflight, there was an increase in the LDN population. Post-flight neutrophils showed altered activation traits, including significantly upregulated surface markers like CD11b, CD80, CD86 on NDN, and CD11b, CD69 on LDN. Reactive oxygen species (ROS) and nitric oxide (NO) production capacity was also enhanced. Post-flight neutrophils, particularly the LDN subpopulation, significantly suppressed IL-2 and tended to suppress IFN-γ secretion, although T cell proliferation was not significantly changed. In conclusion, neutrophils in the circulation of astronauts soon after return to Earth displayed augmented suppressive capacities on T cells.