Signal transduction in T cells: an overview.

The mitogenic in vitro activation of human peripheral blood lymphocytes is severely depressed in space as well as in models of low gravity conditions on ground. The mechanism of T-cell activation is very complex; 3 signals are required for full activation. A series of experiments performed in space and in modeled low gravity on ground have shown that a failure in the delivery of the second signal--interleukin-2--is one of the reasons for the impaired activation. The cytoskeleton plays a key role in several steps of the mitogenic activation; (1) in the binding of the mitogen to the cell membrane and the subsequent patching and capping of the receptors, and (2) in the transduction of the signals from the membrane to the nucleus. Changes in the cytoskeletal structures of vimentin and tubulin observed in cells exposed to low gravity conditions may have influenced the correct signal transduction.