21st CENTURY

main cause of decreased counts of monocytes and macrophages
or the increase of neutrophils postflight. Although
these substances are shown to account for changes in immune
system responses and there is also evidence for direct
interaction between the nervous system and immune
system, this theory falls short of explaining the fact (among
others) that several parameters of blood analysis remain
altered for a significant period of time postflight. It seems
that such theories are presented because of a lack of a more
convincing approach and the difficulty, at present, of conducting
the many onboard experiments needed to clarify
the findings.
Even if there have been no serious health problems on
U.S. space missions so far, the findings concerning immune
system changes are of major significance and must
be followed up closely. The question might arise, can astronauts
who have been in a zero-gravity environment such as
the space station safely return to Earth? In July 1985, an ad
hoc working group convened by the NASA Life Sciences
Research Office expressed a similar view: "The good health
of space crews may be deceptive because patients with
severe neutrophil dysfunction can go months or even years
without a major infection, only to die of an overwhelming
microbial infection at a later date."
The panel of scientists from the fields of biology, medicine,
and immunology referred also to the cases of gingivitis
observed in several Skylab astronauts, which could
reflect a neutrophil dysfunction, such as an impairment of
cell-surface adhesion reactions. Patients with recurrent, severe
bacterial infections associated with functional deficiencies
of their neutrophils have severe gingivitis. "It is
important to determine whether abnormal neutrophil
function occurs in spaceflight, for, in long-term missions,
impaired neutrophil function could be disastrous," the panel
said.
Other findings of microbiological studies after long-term
spaceflights were published by Soviet researchers in 1979.
The observations included: changes in the number of representatives
of normal microflora and increased number of
foci of pathogenic microflora on the skin of carriers; the
appearance on upper respiratory tract mucous membranes
of organisms not normally present; the temporary colonization
by pathogenic staphylococci on mucous membranes
of previous noncarriers by intracrew microbial exchange;
a tendency toward increased virulence of pathogenic autoflora;
increased concentration of microorganisms including
certain pathogens in cabin air and on internal surfaces;
and an apparent development of microbiological and
immunological conditions favoring increased susceptibility
to postflight infections. Although there had not been such
dramatic changes during spaceflights in the past, Soviet
researchers in 1980 reported that a certain hypersensitivity
to microallergens of the normal flora of the body had developed
in cosmonauts during a 175-day space flight.
The Soviet findings, similar to those in U.S. spacecraft,
indicate the dynamic adaptability that bacteria, viruses, fungi,
and other microorganisms have when brought into a
new environment. Microorganisms potentially dangerous
for man, but checked by the immune system under normal
conditions, may suddenly find a more favorable environ-
Figure 2
$LOOD CELL MASS IN CREW^
OF 3 SKYLAB MISSIONS
All astronauts and cosmonauts showed a significant
decrease in ted blood cells. Production of red blood
cells begins t -> slow down after30 days in space. Shown
here are the recovery curves for red blood cell mass,
based on bo\h inflight and postflight measurements.
Source: A.E. Nicog< ssianandJ.F. Parker, Space Physiology and Medicine, NASA,
1982, p. 213.
ment that coulc improve even more when there is an additional
impairrient of the human immune system. Since
man cannot sur/ive in an absolutely sterile condition, the
question is, ho\ i can man control the microflora he brings
into space in avay that is beneficial?
Interesting re iearch about life in total isolation from normal
microflora (sterile air, water, and food) concluded that
such conditions lead to a significant simplification of intestinal
microflora where some species disappear altogether.
At the same tim< i, the remaining intestinal flora are increasingly
less able t) suppress the proliferation of pathogenic
strains.
In a hypothet cally extreme case of simplification of the
intestinal flora, i pace travelers returningto Earth could suffer
a microbial s nock that was described by a researcher as
"the precipitous and harmful action of microorganisms and/
or their produc s on the host." Maintenance of a normal,
diversified intes tinal microflora is considered essential as a
host defense mi ichanism, and apparently this requires periodic
reexposu e to microorganisms in order to stimulate
the immune sys em.
Two well-researched situations paralleling conditions in
a spacecraft are the crews of nuclear submarines during
typical 60-day p; trols and personnel of South Pole stations
who live in tota isolation for several months. In one such
station, outbre; ks of common colds occurred 17 weeks
after complete solation, that is, long after the accepted
incubation periods of human respiratory viruses and at a
time when the i Production of new viruses was apparently
impossible. There are also two reports of mid-patrol outbreaks
of respira tory infections in nuclear submarine crews.
21st CENTL RY November-December 1988 69