Early T-cell Activation, an Experiment on STS-107
Induction of synthesis of the interleukin-2 receptor
Above: Very early molecular events of T-cell activation include a) secretion of interleukin-2 (IL-2), b) expression of the IL-2 receptor (IL-2R) and c) the binding of the IL-2 to the IL-2 receptor (IL-2R) which activates a cascade of events leading to an immune response. We hypothesize that lack of IL-2 receptor expression is probably one of the causes of loss of activation in microgravity. We plan to analyze the pathways of mitogenic signal transduction in T-cells in true microgravity as well as 1-g flight and ground.
This experiment is collaboration between Professor Augusto Cogoli and Professor Millie Hughes-Fulford to study the role of the interleukin-2 receptor in activation of T-cells.
The inhibition of T-cell activation in spaceflight was first discovered in returning Apollo astronauts. It was first thought that systemic (whole body) changes in hormones were responsible. However, early cell biology experiments by Dr. Cogoli in Spacelab in 1983 demonstrated that the activation of T-cells was inhibited in the absence of systemic changes, suggestion that microgravity itself was responsible for loss of T-cell activation.
The objectives of this research project are:
1) To understand why microgravity causes loss of immune function in astronauts.
2) To investigate selected critical steps of T cell activation which include IL2-R expression of message, IL-2 secretion and IL2 binding to IL-2R and other early gene expression.
3) To test the hypothesis that a failure in the expression of IL-2R is causing the loss of activity in microgravity.
4) Analyze the temporal appearance of altered gene expression between ground, m-g flight and 0-g flight samples.
5) Examine the genes that have altered gene expression to see if there is an altered pattern of signal transduction in microgravity.
The main experimental approach will consist of the activation of cultures of purified peripheral blood cells with T cell mitogens in real and simulated microgravity. The specific IL-2R mRNA will be quantitatively determined with the reverse Transcriptase-polymerase chain reaction (RT-PCR) technology, and by Affymatrix gene chips. Signal transduction will be further analyzed by determining the early expression of other genes. The Laboratory of Cell Growth (LCG), headed by Dr. Millie Hughes-Fulford is responsible for analysis of gene expression in T cells. These experiments will provide information on how microgravity changes the activation of the T-cell in flight and will give us valuable information on the mechanism of action behind the lack of T-cell activation in astronauts. Cell signaling begins at the cell surface with the T-cell activators and various signal transduction pathways then internalize the signals for activation. Ground studies show that several pathways are at work during the early stages of T-cell activation, including the MAPK (mitogen activated protein kinase) ERK-2 (extracellular-signal regulated kinase), Protein kinase A (PKA) and protein kinase C (PKC). See pathway schematic below for more details. Analysis of the STS-107 samples grown on the shuttle will allow us to analyze which of these pathways is not functional in microgravity.
Figure 2 Above: Signal transduction pathways that may be affected by microgravity
From studies such as these, we will be able to find the basic biological cause of blunting of the immune system in astronauts.
BioPack is an ESA facility for biological experiments in space presently under development and financed by three partners: ESA, the Netherlands and Switzerland. BioPack will bridge the gap between BioRack flown for the last time in 1997 and Biolab, the biological facility that will become operational in the international space station in 2004. The Space Biology Group will co-ordinate the industrial and scientific activities of the Swiss participation within the financial envelope of the PRODEX program of ESA. STS-107 will be the first flight for Biopack.
Earth Benefits and Applications
All terrestrial life began in a gravity field. This study examines alterations of early T-cell activation microgravity gives us the unique opportunity to examine the role of Earth's gravity in immune function. In the late 60's returning Apollo astronauts were found to have reduced immune function after spaceflight, taking approximately 7 days to recover normal function. Later studies by Dr. Cogoli demonstrated changes in the T-cells during exposure to microgravity. This current program will examine the expression of IL-2, and the three IL-2 receptor subunits (a,b,g) in microgravity with and without an artificial 1g gravity vector and compare those results with ground controls. These studies will show the regulation of the earliest signals that cause the T-cell to activate and the role of normal earth's gravity in that signaling.
Other STS mission experiments from our lab can be found at:
Principal Investigator: NASA: Dr. Millie Hughes-Fulford
V.A. Medical Center and NCIRE, San Francisco, California
Principal Investigator: ESA: Dr. Augusto Cogoli
ETH, Zurich, Switzerland
Project Scientist: Marilyn Vasques
NASA Ames Research Center, Mountain View, CA
Author: Dr. Millie Hughes-Fulford