Masters Thesis Defense - Recovery of Con A-induced Activation by MMG-Exposed Balb/c Mouse Splenocytes
Date: December 13, 2004
Time: 12:00 PM
Location: Hagerty Library, Room: 302
Donald M. Simons
Advisors: Elizabeth M. Gardner, Ph.D. and Peter I. Lelkes, Ph.D.
Spaceflight presents a novel environment for the human body and many physiological changes occur as a consequence, including depression of the cell-mediated immune response. This inhibition could be due to a number of factors present in the spaceflight environment, most notably stress. However, recent, in vitro experiments performed in-flight have shown that microgravity alone is sufficient to inhibit the activation of T lymphocytes. Detailed investigation of the mechanisms behind this inhibition, however, has been problematic due to the limited opportunities for experimentation during spaceflight. As a result, several ground-based models have been developed that can mimic certain aspects of spaceflight. The rotating-wall vessel (RWV) bioreactor was developed by NASA as a ground-based analog emulating some aspects of the microgravity environment (modeled microgravity, MMG) encountered by cells cultured in vitro during spaceflight. The RWV bioreactor is a low-shear three-dimensional suspension culture venue that is capable of reducing the gravitational force experienced by cultured cells to 1/100th of normal earth gravity. Studies of impaired immune dysfunction using RWV technology have correlated well with the results from spaceflight.
This investigation utilized an RWV model of microgravity to examine the inhibitory effects of MMG on the activation of Balb/c mouse splenocytes stimulated with the pan-specific T cell mitogen concanavalin A (Con A). The purpose of this research was to examine the hypothesis that cells exposed to short durations of MMG are capable of recovering activation if returned to 1-g, but for longer durations of MMG-exposure secondary effects due to prolonged lack of stimulus begin to erode the cells ability to recover if returned to 1-g.
The results of these studies show that secondary inhibitory effects are present by 12-hrs of MMG exposure, and that by 24-hrs in MMG these effects have completely quenched the cells ability to recover the proliferative response. However, depressed activation could not be accounted for by a loss of viable cells, as T cells of both subsets were found to survive MMG exposure equally well. Furthermore, recovering cells were also found to be equally sensitive to mitogen as cells that had spent no time in MMG, based on the equal percentages of CD25 and CD69 positive cells seen between the two groups. The rate at which the cells recovered from MMG exposure was found to be no different from cells cultured for similar durations at 1-g, indicating that the capacity to signal remains intact following short durations of MMG-exposure. Taken together, these results indicate that secondary mechanisms, which are sensitive to inactivation rather than microgravity, are likely responsible for permanent inactivation of T cells cultured for 24-hrs or more in MMG.
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