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 leukocy
tes (mainly lymphocytes and monocytes as accessory cells) in the prese
nce of the mitogen concanavalin A was studied in the centrifuge micros
cope NIZEMI at 0 x g. Aggregates (formed by intercellular bindings of
membrane glycoproteins via the tetravalent alpha-glucoside ligand conc
anavalin 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 cor
responding aggregates in the ground control. The findings are of prima
ry importance since they confirm the indirect evidence we had from ear
lier Spacelab experiments and demonstrate that cell-cell contacts are
occurring also in microgravity. In addition, single cells in 0 x g sho
w a significant higher locomotion velocity than the cells at 1 x g. Th
e fact that the locomotion capability is not decreased during the 78-h
incubation with concanavalin A provides further evidence that the cel
ls are not proceeding through the cell cycle.