The effect of microgravity on thein vitro NK cell function during six International Space Station Missions

The level of natural killer (NK) cytotoxic activity was measured during co-cultivation of human lymphocytes and target cells (K-562) in microgravity. Flight experiments were carried out using special instrumentation, the “Fibroblast-1 “ cassettes, in the frame of Russian scientific program during six ISS missions. Lymphocyte suspensions from human venous blood were used in experiments during short-term flights on six ISS missions (7–12). Russian space crew members performed the experiments after Soyuz docking. The first step was mixing lymphocytes and3H-labeled K-562 cells and their incubation at 37°C during 24 hs; the second step was filtration of the cell suspension. The frozen medium and filters were analyzed for the cytokine level and cytotoxic activity after landing. It was found that lymphocytes with different basal levels of cytotoxic activity kept the ability of recognizing and lysing malignant cells. In microgravity, cytotoxity increased to 160% of the basal levels. Donor individual features modulated the magnitude of the increase. The measurement of interleukin levels (TNF-α, IL-1, IL-2) in medium showed that synthesis of TNF-α increased during cell co-cultivation in microgravity. The level of IL-2 was very low inflight and ground control samples. The production of IL-1 by lymphocytes decreased after in-flight incubation. The results indicate that microgravity did not disturb the cytotoxic function of immune cells in vitro during 24 h incubation with specific target cells.