IMMUNE-RESPONSES IN SPACE-FLIGHT

Space flight has been shown to have profound effects on immunological parameters of humans, monkeys and rodents. These studies have been car ried out by a number of different laboratories. Among the parameters a ffected are leukocyte blastogenesis, natural killer cell activity, leu kocyte subset distribution, cytokine production - including interferon s and interleukins, and macrophage maturation and activity, These chan ges start to occur only after a few days space flight, and some change s continue throughout long-term space flight. Antibody responses have received only very limited study, and total antibody levels have been shown to be increased after long-term space flight. Several factors co uld be involved in inducing these changes. These factors could include microgravity, lack of load-bearing, stress, acceleration forces, and radiation. The mechanism(s) for space flight-induced changes in immune responses remain(s) to be established. Certainly, there can be direct effects of microgravity, or other factors, on cells that play a funda mental role in immune responses. However, it is now clear that there a re interactions between the immune system and other physiological syst ems that could play a major role. For example, changes occurring in ca lcium use in the musculoskeletal system induced by microgravity or lac k of use could have great impact on the immune system. Most of the cha nges in immune responses have been observed using samples taken immedi ately after return from space flight. However, there have been two rec ent studies that have used in-flight testing. Delayed-type hypersensit ivity responses to common recall antigens of astronauts and cosmonauts have been shown to be decreased when tested during space flights. Add itionally, natural killer cell and blastogenic activities are inhibite d in samples taken from rats during space flight. Therefore, it is now clear that events occurring during space flight itself can affect imm une responses. The biological significance of space flight-induced cha nges in immune parameters remains to be established; however, as durat ion of flights increases, the potential for difficulties due to impair ed immune responses also increases.