21st CENTURY

Epidemiological control also included the families of primary
contact persons. The schools attended by astronauts'
children provided daily reports about sickness, and the
local health commissioners were asked to analyze any conspicuous
case of sickness that erupted in the neighborhoods
of primary contact persons.
The Health Stabilization Program was highly successful,
and Apollo flights 14-17 showed a dramatic reduction in the
outbreak of diseases in astronauts, both preflight and in
flight (see table).
For a journey to Mars, medical precautions will assume
an even greater role because the space travelers will be on
their own once they have been launched on the trajectory
toward Mars, and a serious illness could potentially doom
the whole enterprise.
The Immune System and Zero Gravity
The effects of zero gravity on the human immune system
may be the most significant problem for the long-term survival
of man in space. For example, it has been observed by
U.S. and Soviet researchers that microflora in isolation in
the spacecraft undergo pathological changes that favor the
development of potentially dangerous organisms. We must
be sure that such a process will not get out of control and
overwhelm the immune defenses of space travelers at a
point where they already suffer from immunosuppression
for other reasons.
Man will always carry his peculiar microflora into space,
since complete sterilization from all microorganisms is not
possible and, in fact, not even desirable. We must therefore
know more about the interchanges between the human
immune system and the conditions of an artificially created
environment. Several important observations about how
the immune system reacts to zero-gravity conditions have
been made during the Space Shuttle and Skylab missions:
• The sensitivity of peripheral lymphocytes has been significantly
depressed (39 percent to 82 percent) postflight in
almost all Skylab crew members; this group of immune
cells showed a diminished ability to react appropriately to
invading microorganisms. This decreased blastogenic sensitivity
of lymphocytes was detected after stimulation of
these immune cells by mutagenic substances.
• Increased levels of neutrophils (another group of white
blood cells) observed in many astronauts were maintained
up to seven days postflight.
• Cum inflammation (gingivitis) developed in several
Skylab astronauts.
• There were decreased counts postflight of lymphocytes,
eosinophils, and monocytes—all immune system
cells.
• Sporadic bacterial contamination of air and drinking
water occurred.
All of the measurements were made on astronauts after
they returned to Earth, because the equipment needed to
do the blood analysis was not carried on board.
Soviet investigations during the Salyut 6 program of 1977-
1981 confirmed the U.S. findings concerning the reduced
sensitivity of lymphocytes. Soviet researchers also reported
other immunological changes in cosmonauts postflight, including
decreased counts of T-lymphocytes and dimin-
68 November-December 1988 21st CENTURY
Before man went into space, monkeys tested the effects of
spaceflight. Here, monkeynaut Sam, in a protective suit, is
lifted out of his flight container after a 1959 flight. He was in
perfect health.
ished reactivity and proliferating capability of these cells.
At the end of a 185-day spaceflight, blood tests of cosmonauts
showed decreased values for T-helper and killer cells.
Again, the reactivity of lymphocytes after blastogenic stimulation
was depressed. Additionally, lymphocytes showed
a decreased production of alpha-interferon, a key substance
in the coordination of the human immune system.
It should be noted that blood analysis of AIDS patients
shows similar patterns of change, in part. As a consequence,
infections that are rare or almost nonexistent in
healthy humans become deadly killers for AIDS-infected
people. Whatever the biological-immunological dynamic
that leads to an AIDS-like syndrome in space, it is obvious
that no HIV virus as currently conceived is necessary to
effect the changes that are closely associated with the HIVcaused
AIDS syndrome. Although it would be absurd to say
that space travelers may die of AIDS, space medical research
should concentrate further efforts to uncover the
biological process that leads to an apparent immune incompetency
in space.
Many experts tend to explain changes in blood cell counts
as caused by astronauts' increased stress during critical
phases of flight. Increased levels of cortico-steroids and
"stress hormones" like epinephrine are mooted to be the