No abstract

Life on Earth developed in the presence and under the constant influence of gravity. Gravity has been present during the entire evolution, from the first organic molecule to mammals and humans. Modern research revealed clearly that gravity is important, probably indispensable for the function of living systems, from unicellular organisms to men. Thus, gravity research is no more or less a fundamental question about the conditions of life on Earth. Since the first space missions and supported thereafter by a multitude of space and ground-based experiments, it is well known that immune cell function is severely suppressed in microgravity, which renders the cells of the immune system an ideal model organism to investigate the influence of gravity on the cellular and molecular level. Here we review the current knowledge about the question, if and how cellular signal transduction depends on the existence of gravity, with special focus on cells of the immune system. Since immune cell function is fundamental to keep the organism under imnological surveillance during the defence against pathogens, to investigate the effects and possible molecular mechanisms of altered gravity is indispensable for long-term space flights to Earth Moon or Mars. Thus, understanding the impact of gravity on cellular functions on Earth will provide not only important informations about the development of life on Earth, but also for therapeutic and preventive strategies to cope successfully with medical problems during space exploration.

In order to enable kinetic online measurements in cell cultures during exposure to altered gravitational stimulation a new device has been constructed. The analysis principle is based on photon counting with a photomultiplier tube (PMT). The system can work in a rotating mode (clinostat principle) as well as in 1 g conditions. Biological verification was successfully performed with a Luminol-based luminescence measurement of the immune reaction of mammal macrophages. An identical methodical approach is foreseen for an ISS experiment (TRIPLE LUX). Alteration of the rotation speed of the PMT clinostat (60 and 2 rotations per minute-rpm) resulted in a speed-dependent decrease of the luminescent signal, contributing to the current discussion whether and how fast rotation of a sample around one axis perpendicular to the direction of the gvector provides the condition of functional weightlessness or omnilateral mechano-(gravi-) stimulation.