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EFFECT OF GRAVITY CHANGES ON THE CYTOSKELETON IN HUMAN LYMPHOCYTES.  M. Cogoli-Greuter. Space Biology Group, ETH Technopark, Technoparkstr. 1 CH-8005 Zьrich.

   A series of experiments performed in space as well as in modelled microgravity on ground have shown that 1) The mitogenic activation of human lymphocytes in vitro is severely depressed; 2) Binding of the mitogen Con A to membrane glycoproteins is unchanged, but patching and capping are slightly retarded; 3) Cell-cell interactions and aggregate formation are occurring, although space aggregates are smaller than the respective ground controls; 4) Single cells show autonomous movements with a higher velocity than at 1xg; 5)  The amount of interleukin-2 receptor (IL-2R) and interleukin-2 (IL-2) measured as protein secreted in the medium is depressed; 6) The expression of both IL-2 and IL-2Ra genes is significantly inhibited in modelled microgravity; and 7) 1-2 % of genes monitored using cDNA microarray hybridization technology show significant modulation in response to short term microgravity.
   Changes in cell activation and signal transduction as well as cell movements and aggregate formation may be related to changes in the cytoskeleton. In fact marked alterations in the structure of the intermediate filaments of vimentin as well as the microtubules network are observed in microgravity. Most evident is the appearance of large bundles in the vimentin structure, significantly increased in the samples exposed to 30 seconds of microgravity compared to the in-flight 1 g controls.  These results indicate that direct effects of microgravity on the cytoskeleton in human lymphocytes are likely.