Alterations in adaptive immunity persist during long-duration spaceflight.

Area of Science:

• Spaceflight immunology
• Human physiology in space
• Adaptive immunity

Background:

• Immune system alterations during long-duration spaceflight remain largely unknown.
• Assessing adaptive immune parameters in astronauts during 6-month International Space Station (ISS) missions is crucial.

Purpose of the Study:

• To evaluate phenotypic and functional changes in the immune system of astronauts during 6-month orbital spaceflights.
• Investigate the persistence of immune alterations throughout the mission duration.

Main Methods:

• Blood samples collected from 23 astronauts before, during, and after 6-month ISS expeditions.
• In-flight samples analyzed within 48 hours of collection on Earth.
• Assessed leukocyte distribution, T-cell function, virus-specific immunity, and cytokine production profiles.

Main Results:

• Observed leukocyte subset redistribution, elevated white blood cell counts, and altered CD8+ T-cell maturation.
• General T-cell function (CD4+ and CD8+) was reduced throughout the 6-month flight, indicating a potential activation threshold shift.
• Reduced production of key cytokines (IFNγ, IL-10, IL-5, TNFα, IL-6) persisted during spaceflight, with altered IL-2 and IL-8 production post-flight and during lipopolysaccharide stimulation.

Conclusions:

• Immune system alterations are persistent during long-duration spaceflight.
• These immune changes may increase clinical risks for astronauts on exploration-class missions.
• Development of countermeasures is essential to mitigate immune risks in deep space exploration.