It is currently unknown whether immune system alterations persist during long-duration spaceflight. In this study various adaptive immune parameters were assessed in astronauts at three intervals during 6-month spaceflight on board the International Space Station (ISS). To assess phenotypic and functional immune system alterations in astronauts participating in 6-month orbital spaceflight. Blood was collected before, during, and after flight from 23 astronauts participating in 6-month ISS expeditions. In-flight samples were returned to Earth within 48 h of collection for immediate analysis. Assays included peripheral leukocyte distribution, T-cell function, virus-specific immunity, and mitogen-stimulated cytokine production profiles. Redistribution of leukocyte subsets occurred during flight, including an elevated white blood cell (WBC) count and alterations in CD8+ T-cell maturation. A reduction in general T-cell function (both CD4+ and CD8+) persisted for the duration of the 6-month spaceflights, with differential responses between mitogens suggesting an activation threshold shift. The percentage of CD4+ T cells capable of producing IL-2 was depressed after landing. Significant reductions in mitogen-stimulated production of IFNγ, IL-10, IL-5, TNFα, and IL-6 persisted during spaceflight. Following lipopolysaccharide (LPS) stimulation, production of IL-10 was reduced, whereas IL-8 production was increased during flight. The data indicated that immune alterations persist during long-duration spaceflight. This phenomenon, in the absence of appropriate countermeasures, has the potential to increase specific clinical risks for crewmembers during exploration-class deep space missions. Long space voyages could pose health risks resulting from changes to astronauts' immune systems, warn NASA scientists. A team led by Clarence Sams of NASA's Johnson Space Center in Houston analyzed blood samples taken from astronauts before, during, and after six-month stays on the International Space Station. They detected a variety of persistent changes in immune cell numbers and functions, and altered production of signaling molecules that mediate the immune response. During extended space flights, such as missions to Mars, these changes could cause medical problems such as increased susceptibility to infectious disease, allergies, altered wound healing. It is also possible that the risk for cancer or the development of autoimmune disease would also be elevated. The characterization of immune changes during flight represents the first step in determining the need for immune-specific countermeasures that would improve the health and safety of astronauts on extended space missions.

Alterations in adaptive immunity persist during long-duration spaceflight