Humoral and cellular immunity in cosmonauts after the ISS missions

Spaceflight effects on the immune system were studied in 30 cosmonauts flown onto the International Space Station (ISS) for long- (125–195 d, n=15n=15) and short-term (8–10 d, n=15n=15) missions. Immunological investigations before launch and after landing were performed by using methods for quantitative and functional evaluation of the immunologically competent cells. Specific assays include: peripheral leukocyte distribution, natural killer (NK) cell cytotoxic activity, phagocytic activity of monocytes and granulocytes, proliferation of T-cells in response to a mitogen, levels of immunoglobulins IgA, IgM, IgG, virus-specific antibody and cytokine in serum. It was noticed that after long-term spaceflights the percentage of NK (CD3-/CD16+/CD56+)(CD3-/CD16+/CD56+) cells was significantly reduced compared with pre-flight data (p<0.05)(p<0.05) and NK activity was suppressed by 20–85% as compared with pre-flight data in 12 out of 15 cosmonauts. T-lymphocyte activity was decreased by 25–39% as compared with pre-flight data in 5 out of 13 cosmonauts. However, the relative number of CD3+CD3+, CD4+CD4+ and CD8+CD8+ T-cells did not change. The functional activity of NK and T-cells decreased in some of the cosmonauts after short-term missions. On the other hand, a moderate trend upward of NK cytotoxic activity and proliferative activity of T-cells was observed in some individuals. Concentrations immunoglobulins (IgA, IgM, IgG) and levels of M and G antibodies to herpes simplex virus (HSV), cytomegalovirus (CMV), Epstein–Barr virus (EBV) and herpes virus type 6 (HV6) in serum did not reveal significant changes after long- and short-term flights. Concentrations of cytokines (IL-1β1β, IL-2, IL-4 and TNF-αα) in serum changed in an apparently random manner as compared with values before long- and short-term missions. Despite the fact that many improvements have been made to the living conditions of aboard the ISS our investigations demonstrate the remarkable depression of the immunological function after the ISS missions. These results suggest that the clinical health risk (related to immune dysfunction) will occur during exploration class missions.