Decreased non-MHC-restricted (CD56+) killer cell cytotoxicity after spaceflight

1 Enterprise Advisory Services Inc., Houston 77058; 2 Department of Tumor Biology, The University of Texas M. D. Anderson Cancer Center, Houston 77030; and 3 Life Sciences Research Laboratories, National Aeronautics and Space Administration, Johnson Space Center, Houston, Texas 77058 Cytotoxic activity of non-major histocompatibility complex-restricted (CD56 + ) (NMHC) killer cells and cell surface marker expression of peripheral blood mononuclear cells were determined before and after spaceflight. Ten astronauts (9 men, 1 woman) from two space shuttle missions (9- and 10-day duration) participated in the study. Blood samples were collected 10 days before launch, within 3 h after landing, and 3 days after landing. All peripheral blood mononuclear cell preparations were cryopreserved and analyzed simultaneously in a 4-h cytotoxicity 51 Cr release assay using K562 target cells. NMHC killer cell lytic activity was normalized per 1,000 CD56 + cells. When all 10 subjects were considered as one study group, NMHC killer cell numbers did not change significantly during the three sampling periods, but at landing lytic activity had decreased by ~40% ( P