NATURAL-KILLER-CELLS AFTER ALTAIR MISSION

Reduced in vitro NK cytotoxic activity have routinely been observed af ter both prolonged and short-term space flights. This study investigat ed the effects of space flight on NK cell functions, NK cell counts an d the production of IL-2 and TNF by lymphocytes of French-Russian crew members, In the French cosmonaut, after 21 days space flight, the cyt otoxic activity of NK cells, the capacity the NK cells to bind and lys e the individual target cells and the percentage of NK cells were decr eased. In this cosmonaut a twofold reduction TNF production in culture s of lymphocytes stimulated with PMA and with the mixture of PHA and P MA was observed on the first day after landing. However, the activity of the production of TNF in 48-hour PHA-cultures of lymphocytes was un changed and the biological activity of IL-2 was not reduced. The immun ological examination did not detecte any substantial deviations from t he norm in both russian cosmonauts after 197 days space flight. Variou s explanations for decreased cytotoxicity in cosmonauts after space fl ight can be proposed, and these include the defective function of NK c ells and reduced numbers of circulating effector cells.