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The Effect of Changes in Gravity on Human Monocyte Cell (TUR) Phagocytosis.   C.B. Johnson1 1Dept. of Physical and Life Sciences, Texas A&M University-Corpus Christi, TX.

   The function of the immune system is compromised during spaceflight.  Many cellular activities crucial for an effective immune response are diminished in microgravity conditions.  Evidence also suggests that the cytoskeleton is altered in microgravity, potentially leading to some of the noted defects. Phagocytosis is a vital, cytoskeleton-mediated immune process necessary for the clearance of pathogenic microorganisms; therefore alterations to this important process may leave astronauts vulnerable to infection.  The objective of this project was to evaluate if microgravity or hypergravity conditions would alter the phagocytic capacity of a human, monocyte-like phagocytic immune cell (TUR).  Additionally, because of its role in the phagocytic process, rearrangement of the actin portion of the cytoskeleton was also examined. 

   Microgravity and hypergravity conditions were modeled using ground-based systems.  A rotary cell-culture system (RCCS) was used to simulate microgravity, and a novel device called the Hypergravity 3000 (HG3K) was designed and built for the analysis of hypergravity.   Phagocytosis was triggered by the addition of fluorescein-conjugated Escherichia coli bacteria and actin was examined fluorescently using Texas Red-XÒ conjugated phalloidin.  The TUR cells were exposed to either microgravity or hypergravity for a period of 10 days and cells were evaluated for phagocytosis at 1, 4, 12, 24, 48 hours, and at 5 and 10 days. Surprisingly, both microgravity and hypergravity enhanced TUR cell phagocytosis compared to 1 g controls, the peak enhancement (~60%) occurring at 24 hours under both conditions.   This increase slowly decreased over time, however phagocytosis never returned to 1 g levels.  Actin rearrangements were also observed in microgravity and hypergravity exposed cells.  Actin is vital for phagocytic activity; therefore the morphological changes observed may be contributing to the observed phagocytic alterations. Further research utilizing additional cell lines is warranted to fully investigate how changes in gravity alter immune cell phagocytic function.

(Supported by: Texas Space Grant Consortium “New Principle Investigator Grant 2004-2005 ” and Texas Excellence Fund Grant 2005.)