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

Cytotoxic activity of non-major histocompatibility complex-restricted (CD56 (+)) (NMHC) killer cells and cell surface marker expression of peripheral b lood mononuclear cells were determined before and after spaceflight. Ten as tronauts (9 men, 1 woman) from two space shuttle missions (9- and 10-day du ration) participated in the study. Blood samples were collected 10 days bef ore launch, within 3 h after landing, and 3 days after landing. All periphe ral blood mononuclear cell preparations were cryopreserved and analyzed sim ultaneously in a 4-h cytotoxicity Cr-51 release assay using K562 target cel ls. 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 similar to 40% (P < 0.05) from preflight values. Nine of ten astronauts had decreased lytic activity immed iately after flight. NMHC killer cell cytotoxicity of only three astronauts returned toward preflight values by 3 days after landing. Consistent with decreased NMHC killer cell cytotoxicity, urinary cortisol significantly inc reased after landing compared with preflight levels. Plasma cortisol and AC TH levels at landing were not significantly different from preflight values . No correlation of changes in NMHC killer cell function or hormone levels with factors such as age, gender, mission, or spaceflight experience was fo und. After landing, expression of the major lymphocyte surface markers (CD3 , CD4, CD8, CD14, CD16, CD56), as determined by flow cytometric analysis, d id not show any consistent changes from measurements made before flight.