The impact of long-term weightlessness on immunity has been revealed in extended manned space flights. This investigation (a) provided data which illuminates microgravity effects on locomotion and migration of human lymphocytes through an intercellular matrix, a function that is crucial to immunocompetence, (b) tested the adequacy of the Rotating Wall Vessel (RWV), a laboratory-based microgravity simulation environment developed by NASA, and (c) verified the Specimen Temperature Controller which is necessary to control the thermal environment of the living cells inflight. Analysis of in-flight data was performed in the Biotechnology Laboratory at Johnson Space Center.
Cell locomotion was defined as the distance between the microcarrier surface (single-phase microcarrier) or cell/collagen interface (dual-phase microcarrier) and the three leading-edge cells. This measurement was determined by fine focus microscopy using an inverted microscope with phase contrast (Nikon Diaphot, Japan). Using a predetermined calibration factor, this measurement was converted from fine focus units to locomotory distance in micrometers (gin).
In the randomized gravity of the rotating-wall vessel culture system, peripheral blood lymphocytes did not locomote through Type I collagen, whereas static cultures supported normal movement. Although cells remained viable during the entire culture period, peripheral blood lymphocytes transferred to unit gravity (static culture) after 6 hours in the rotating-wall vessel culture system were slow to recover and locomote into collagen matrix. After 72 hours in the rotating-wall vessel culture system and an additional 72 hours in static culture, peripheral blood lymphocytes did not recover their ability to locomote. Loss of locomotory activity in rotating-wall vessel cultures appears to be related to changes in the activation state of the lymphocytes and the expression of adhesion molecules. Culture in the rotating-wall vessel system blunted the ability of peripheral blood lymphocytes to respond to polyclonal activation with phytohemagglutinin. Locomotory response remained intact when peripheral blood lymphocytes were activated by anti-CD3 antibody and interleukin-2 prior to introduction into the rotating-wall vessel culture system. Thus, in addition to the systemic stress factors that may affect immunity, isolated lymphocytes respond to gravitational changes by ceasing locomotion through model interstitium. These in vitro investigations suggest that microgravity induces non-stress-related changes in cell function that may be critical to immunity. Preliminary analysis of locomotion in true microgravity revealed a substantial inhibition of cellular movement in Type I collagen. Thus, the rotating-wall vessel culture system provides a model for analyzing the microgravity-induced inhibition of lymphocyte locomotion and the investigation of the mechanisms related to lymphocyte movement.