Movements and interactions of leukocytes in microgravity.

The mitogenic activation of human lymphocytes resuspended in vitro is dramatically reduced in microgravity. As cell-cell contacts are one of the elements essential for activation, the behaviour of human leukocytes (mainly lymphocytes and monocytes as accessory cells) in the presence of the mitogen concanavalin A was studied in the centrifuge microscope NIZEMI at 0 x g. Aggregates (formed by intercellular bindings of membrane glycoproteins via the tetravalent alpha-glucoside ligand concanavalin A) were found at 0 x g as well as at 1 x g already 12 h after the addition of the mitogen. In general, the aggregates observed at 0 x g after an incubation time of 46 and 78 h were smaller than the corresponding aggregates in the ground control. The findings are of primary importance since they confirm the indirect evidence we had from earlier Spacelab experiments and demonstrate that cell-cell contacts are occurring also in microgravity. In addition, single cells in 0 x g show a significant higher locomotion velocity than the cells at 1 x g. The fact that the locomotion capability is not decreased during the 78-h incubation with concanavalin A provides further evidence that the cells are not proceeding through the cell cycle.