Decreased red blood cell mass during space missions has been recognized since 1977 (Johnson et al., 1977; Leach and Johnson, 1984), but there is no resulting impairment from this “anemia.” The documented fall in erythropoietin levels and the fall in the numbers of reticulocytes indicate that this results from diminished production, not increased cellular destruction (Alfrey et al., 1996). However, because of the diminution of the plasma volume early in the flight, the measured hematocrit levels and red blood cell counts did not fall during flight but were noted after the return to Earth because of the more rapid restoration of plasma volume than the level of red blood cell production. Erythropoietin levels returned to normal in 1 to 2 weeks after landing. In 1990, Koury and Bondurant (1990) hypothesized that erythropoietin prevents programmed cell death in erythropoid progenitor cells, thereby adding significantly to general medical knowledge through research conducted in space. Anemia could become a clinical problem during long-duration space travel, and erythropoietin administration is being evaluated as a countermeasure.
Altered cell-mediated immunity has been reported in a variety of analog environments, including the Antarctic (Tingate et al., 1997) and space (Kimzey et al., 1975, 1977). Escherichia coli and Staphylococcus aureus isolates have also been shown to become more resistant to selected antibiotics during space travel (Lapchine et al., 1986). Although the clinical significance of these alterations has not been determined, the effects on skin and wound infections and wound healing during long-duration space missions could become clinically important.
Preflight isolation techniques for spaceflight crewmembers are reported to have decreased the infection rate for the 3 weeks preflight from about 50 percent to only occasional events (Ferguson, 1977; Ferguson et al., 1977). Gingivitis and skin furuncles are now the primary preflight infections reported (Taylor and Gormly, 1997). Increased shedding of herpesvirus and expansion of Epstein-Barr virus-infected B cells have been reported in the Antarctic environment (Tingate et al., 1997; Lugg and Shepanek, 1999) and in astronauts (Payne et al., 1999). The bases for the divergent changes are not understood. They do, however, indicate the importance of immunology and microbiology to healthy human physiology during space travel and the need for further research in this area of space medicine.