Review

Abstract

Immune responses measured at rest immediately or some hours after exercise training (some with and some without increase in maximal oxygen uptake) gave variable and sometimes conflicting results; therefore, no general conclusions can be drawn. On the other hand, most immune responses were either unchanged (immunoglobulin, T cells, CD4+, and natural killer activity) or decreased (blood properdin, neutrophil phagocytic activity, salivary lysozymes, brain immunoglobulin A and G, and liver B lymphocytes and phytohemagglutinin activity) during prolonged bed rest. Some data suggested that exercise training during bed rest may partially ameliorate the decreased functioning of the immune system. Exercise and change in body position, especially during prolonged bed rest with plasma fluid shifts and diuresis, may induce a change in plasma protein concentration and content, which can influence drug metabolism as well as immune function. Leukocytosis, accompanied by lymphopenia and a depressed lymphocyte response, occurs in astronauts on return to Earth from spaceflight; recovery may depend on time of exposure to microgravity. It is clear that the effect of drugs and exercise used as countermeasures for microgravity deconditioning should be evaluated for their effect on an astronaut's immune system to assure optimal health and performance on long-duration space missions.With the prospect of long-term spaceflight and the potential colonization of the Moon and Mars, the relative confinement and close contact of astronauts and the necessary limitation of medical treatment and facilities will focus more attention on preventive medicine in general, and also on overall functioning of the immune system. The adaptive physiologic deconditioning response of many body systems has been studied extensively during prolonged bed rest (Greenleaf et al., 1976(Greenleaf et al., , 1982Luu et al., 1990) and, to a lesser extent because of operational constraints, during spaceflight (Garshnek, 1989; Nicogossian etal., 1989). Immune system function has not been investigated extensively during exposure to prolonged bed rest or microgravity. Research findings (Chukhlovin and Burov, 1969;