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1 Clinic of Anaesthesiology and 3 Institute for Surgical Research, University of Munich, 81366 Munich, Germany; and 2 Institute of Biomedical Problems, 123007 Moscow, Russia
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ABSTRACT |
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 TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
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The aim of the study was to evaluate
the effects of long-term confinement on stress-permissive
neuroendocrine and immune responses in humans. Two groups of
four male subjects were confined 240 days (group 240) or 110 days (group 110) in two space modules of 100 or 200 m3, respectively. During confinement, none of the
volunteers developed psychic stress as could be examined and verified
by a current stress test. However, in group 240 but not in
group 110, the diurnal rhythm of cortisol secretion was
slightly depressed and the urine excretion of norepinephrine
significantly increased. The innate part of the immune system became
activated as seen by a rise in the number of circulating granulocytes
and the enhanced expression of 
2-integrins. In contrast,
the ratio of T-helper to T-suppressor cells decreased. All these
effects, observed during confinement, were even more pronounced in both
groups when values of endocrinological and immunological parameters
were compared between before and 1 wk after the end of the confinement
period. Hence, return to normal life exerts pronounced effects to a
much higher degree, irrespective of how long or under which conditions
individuals were confined. Because the delayed-type hypersensitivity
skin reaction against recall antigens remained unaffected, it is to be
presumed that confinement appears to induce distinct sympathoadrenergic activation and immunological changes but no clinically relevant immunosuppression.
stress; leukocytes; cortisol; delayed-type hypersensitivity reaction
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INTRODUCTION |
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TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
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SPACEFLIGHT CAN AFFECT EVERY organ system, and it causes a number of physiological changes (immune changes, muscle atrophy, demineralization of bones). Alterations in immune responses during and after spaceflight have been reported in humans (15). Such effects (29, 31) could be a consequence of microgravity and radiation (18, 25). Besides physical forces, environmental stress factors could also play an important role in inflight as well as in postflight changes of the immune response. However, the quantification of environmental stress factors seems to be difficult because isolation, confinement, artificial circadian rhythm, as well as altered social interactions may altogether chronically affect the neuroendocrine stress and immune responses (20).
Because Russian, European, and American space agencies plan to establish long-term presence of people in space [International Space Station (ISS); mission to Mars], ground-based simulation studies are frequently preferred to investigate possible unwanted changes of health under standardized conditions. Accordingly, ground-based studies have been carried out to mimic the effects of low gravitation [e.g., by long-term hypokinesia in head-down tilt (HDT) at 6° (7, 9, 17, 40) or by water immersion (8)]. Confinement can be induced operationally in submarines, polar stations, and deep-sea laboratories as well as during expeditions in the Antarctica. Even deep-sea diving can, to a certain extent, reflect in-space conditions (a return to Earth or surface being impossible for a number of days even in the case of emergency), although hyperbaric conditions (100% oxygen) do not reflect life in space (27). Studies in a slightly pressurized diving chamber, where the conditions of daily life and work resemble those in space, mimic conditions in space better, but they have not yet been studied beyond a duration of 60 days (12).
In the present study, we investigated the isolated effects of group confinement for 110 and 240 days on stress-permissive neuroendocrine and immune responses in humans. To this end, the same variables were determined that were shown in a previous ground-based study to be sensitive enough for the detection of psychic stress and neuroendocrine-related changes of the immune system in healthy volunteers who had been subjected to HDT (5). Because the number and volume of blood samples allowed to be drawn were strictly limited, overall reactivity and cooperation of the nonspecific and specific parts of the immune response were additionally assessed by the delayed-type hypersensivitiy (DTH) reaction of the skin against a panel of standardized recall antigens.
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MATERIALS AND METHODS |
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TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
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SFINCSS99, Study Groups, and General Conditions
In the future, ISS astronauts and cosmonauts will form one international crew living in different national space modules for longer periods of time. To simulate these conditions, the Simulation of Flight of the International Crew on the Space Station (SFINCSS99) project was carried out in the Institute of Biomedical Problems in Moscow in 1999 and 2000. All the subjects investigated were selected in accordance to medical criteria of cosmonaut selection and already had experience in extreme environmental condtions (e.g., member of astronaut or cosmonaut team). The general conditions were set to mimic the environmental conditions (gas composition, pressure, humidity and temperature, noise) as well as the living conditions on board the ISS. Regarding the latter, main inflight operations were simulated (e.g., docking, visiting groups), communication with mission control was performed (each 90 min for 30 min), and nutrition and sanitary concerns were mimicked. Daily life was subjected to a 24-h schedule: 8 h of daily work, 8 h of sleep, 3 h of spare time, 2 h of physical training, 2 h for meal preparation and eating, and 1 h for personal hygiene. Day and night cycles were kept by external timers (bright light in the module from 7 to 23 h).After approval from the local ethical committee and receipt of informed consent, the first group of four healthy Russian male subjects (aged 41.8 ± 5.5 yr) was confined for 240 days in a container resembling a Russian space module (100 m3) where working zone and sleeping area were combined in one room (further designated as group 240). The second group of four subjects (3 Russian and 1 German volunteer, aged 38.2 ± 9.0 yr) spent 110 days (further designated as group 110) in the second chamber that was larger (200 m3) and contained a separate sleeping area for each subject. Both modules were connected to each other. The number of individuals who could be investigated was limited by the volume of the space modules studied.
According to the study protocol, saliva samples and tests of psychic well-being were taken before confinement (Pre 110 and Pre 240), monthly during confinement [group 110: months 1-3 (M1-M3); group 240: months 1-7 (M1-M7)], and 1 wk after the end of the confinement period (Post 110 and Post 240). Peripheral blood samples were withdrawn from the cubital vein before and 1 wk after confinement (Pre and Post 110 and Pre and Post 240) and additionally monthly (M1-M7) during confinement in group 240 to evaluate possible changes of white blood cells. In addition, DTH skin reaction against seven recall antigens was determined in both groups before and after confinement. Blood samples were analyzed in part immediately after acquisition or prepared and stored for further analyses.
No true control group (a matched group of individuals subjected to daily life outside of the chamber for the same period of time) could be studied because of the long-term approach of the present investigation and because of financial reasons. Hence, in agreement with the design of previous studies (5, 24), changes were compared to the Pre values within each group.
Current Stress Test
The current stress test (CST) was developed and validated by German psychologists (21) and was already applied during a study on the effects of 120 days of 6° HDT (5). The test is composed of six pairs of contradictory feelings of increasing intensities between which the subject has to decide. From the sum of values obtained, the final CST score is calculated, which may range from 1 (no stress) to 6 (maximal stress). The CST is a self-estimating, one-page paper test that is performed within 1 min and whose answers cannot be recalled by the test person because of the composition of the questionnaire.Cortisol
Because glucocorticoids are known to be periodically secreted in response to a variety of environmental and hormonal stimuli (e.g., psychic stress and physical exercise), which alone and/or together with cortisol might affect the immune system, free cortisol was determined repeatedly in saliva samples collected in the morning (8:00 AM) and in the evening (8:00 PM). Saliva was collected by chewing on a cotton swab for 30-45 s, which was stored in a SALIVETTE device tube (Sarstedt, Nürnbrecht, Germany). Samples were frozen, and free-cortisol concentrations were quantified by RIA according to the instructions of the manufacturer (Cort-CT2 kit, CIS Bio International, Gif-sur-Yvette, France). To monitor the circadian rhythm of cortisol secretion, the ratio between morning and evening (m/e) cortisol values was calculated.Prolactin
EDTA-containing plasma was aliquoted from blood specimen after centrifugation (600 g for 5 min at 2°C) and stored at
80°C until determination of prolactin by using a commercially
available assay (ELECSYS, Roche Diagnostics, Mannheim, Germany).
Catecholamines
Dopamine, norepinephrine, and epinephrine were determined in 24-h urine samples collected monthly in each group at the same time points when saliva was collected and blood samples were withdrawn. After collection of urine in a container prefilled with hydrochloric acid (10%), urine samples were kept frozen until analysis by HPLC (Chromsytems, Martinsried, Germany). The amounts of catecholamines secreted was calculated on the basis of total catecholamine excretion in urine pooled during 24 h (µg/24 h).Cell Counts
The concentration of lymphocytes, polymorphonuclear leukocytes (PMNL), and monocytes was determined from EDTA-anticoagulated whole blood specimen (Coulter multisizer, Coulter Electronics, Luton, UK).2-Integrins
2-integrins, fluorescence intensities were analyzed by
using a FACScan (Becton Dickinson, San Jose, CA). The
expression of adhesion molecules was thereafter calculated as
previously described (32) and expressed as relative
fluorescence units. Because determination of lymphocyte surface
antigens and 2-integrins could not be performed in
Moscow, blood samples were separated and transported to Munich, Germany at 20°C (for Simultest IMK) and at 0°C (2-integrins)
and analyzed within 12 h after blood sampling. Additional control
experiments were carried out to detect possible alterations due to
transportation and delayed determination.
Superoxide Anion Production by Phagocytes in Diluted Whole Blood
The production of the superoxide anions (O
6 M, Sigma Chemical, Deisenhofen,
Germany). For this purpose, a total of 1 ml of heparinized
whole blood was aliquoted in four plastic tubes each prefilled with
prewarmed (37°C) reaction mixture of 1.4 ml of Hanks' buffered salt
solution, cytochrome c (0,625 mg/ml), and cytochalasin B
(2.5 µg/ml). Tube 1 had no further additives, whereas
tubes 2 and 3 contained fMLP in the absence and
presence of superoxide dismutase (50 U/ml). Tube 4 contained superoxide dismutase (50 U/ml). All concentrations mentioned above are
final concentrations. After incubation of the reaction mixtures at
37°C for 15 min, cellular components were pelleted by centrifugation (5 min, 600 g). Thereafter, the supernatants were
transferred to a microtiter plate, and the absorbances were determined
in triplicates on a multichannel automated photometer (550 nm fitted with a 630-nm interference filter, Dynatec MRX 7000, Dynatec
Laboratories, Alexandria, VA). From the difference between the
absorbances determined in samples 2-4 and samples
1-3, the stimulated and the spontaneous production of
OBecause of technical problems at the time points M2 to M5,
O
T and B Cells
To demonstrate possible changes of the specific part of the immune system, the percentages of functionally different subpopulations of lymphocytes were determined. To this end, we measured the expression of cell surface differentiation [cluster of differentiation (CD)] antigens of blood lymphocytes: CD3 on all T lymphocytes; CD4 and CD8 on T-helper, T-suppressor, and T-cytotoxic lymphocytes; and CD19 only on B-lymphocytes. CD56 and CD16 are coexpressed predominantly on a specific subgroup of lymphocytes, the natural killer (NK) cells. All the cell surface markers described here were determined by incubation of cells with specific fluorochrome-labeled monoclonal antibodies and subsequent analyses by flow cytometry (FACScan, Becton Dickinson) according the instruction of the assay manufacturer (Simultest IMK-Lymphocyte, Becton Dickinson). Further details of FACS-based immunophenotyping are published elsewhere (5).Cytokines and C-reactive Protein
EDTA-anticoagulated blood specimens were centrifuged at 600 g for 5 min in a cooled centrifuge (2°C) and stored at80°C until determination of plasma cytokines and C-reactive protein
(CRP). Quantitative analysis of interleukin-6 (IL-6), interferon-
(INF-), and CRP was performed by commercially available assay
(TINA-Quant, Roche Diagnostics).
DTH Reaction
To monitor cellular immunoreactivity, the DTH reaction was tested. The standardized recall antigen multitest skin test (Immignost, Biosyn, Fellbach, Germany) contains seven different antigens that are injected by a test stamp intracutaneously by a slight push on the stamp toward the skin of the inner arm. To determine the DTH, the erythemas formed 48 h later were determined in their smallest and largest diameters, and the mean diameter was calculated. The test can be applied repeatedly, without sensibilization and with high reproducibility (16). It was performed in both groups before confinement (Pre) and 7 days after confinement (Post).Statistics
The present study is a part of a large study coordinated by the Institute of Biomedical Problems in Moscow. Although one would have wished to investigate more than four subjects per confinement group, logistic, personnel, and financial resources set clear limits. Blood, saliva, and DTH analyses were performed in both groups before and after confinement, whereas in group 240 blood samples could be additionally taken during the confinement period. Because living conditions were different between the groups (e.g., volume of chamber), each group was analyzed separately despite the fact that the modules of both groups were connected to each other and social interaction between the groups was possible at any time. Statistical analyses of each group were performed with respect to the limitations of the small number of subjects. Data were tested for normal distribution by one-sample Kolmogorov-Smirnov test and compared with the Pre values of the same subjects by repeated-measures ANOVA with adjustment for multiple comparisons by Bonferroni. Two-tailed level of significance was set at P < 0.05. Data are presented as means ± SE. All statistical analyses were performed by SPSS program 10.0 (SPSS, Chicago, IL).| |
RESULTS |
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TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
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Group 110: Psychoneuroendocrine Changes
CST score.
The averaged CST scores in group 110 showed only small
variation during confinement (M1-M3: CST < 2.3) in the range
of values usually observed in persons having no stress (normal range
2.4-2.8). After confinement, the mean CST score increased
slightly (Post 110: 2.67; Table 1).
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Cortisol. Morning and evening concentrations of free cortisol in saliva were elevated in Pre confinement. This was also the case during confinement, but morning and evening cortisol values always showed a circadian rhythm with higher levels in the morning followed by a decline in the evening. The calculated m/e was in the normal range (3-5) before and during confinement (Pre 110, M1-M3). Interestingly, a drop in m/e was observed after the end of confinement (Post 110: 1.4; Table 1).
Prolactin. The plasma concentrations of prolactin were almost doubled after confinememt (Pre: 7.63 ng/ml; Post: 13.65 ng/ml), but they still remained in the physiological range (3-23 ng/ml; Table 1).
Catecholamines. Total urine secretion (µg/24 h) of dopamine and epinephrine remained unchanged during the entire observation period. This was also the case for the urine concentrations of norepinephrine, with the exception of a significant increase after the end of confinement (P < 0.05, Post 110 vs. Pre 110 or M3; Table 1).
Group 110: Immunological Changes
Cell counts.
Number of blood leukocytes increased after confinement (Pre 110:
3.83 × 103/µl; Post 110: 4.49 × 103/µl). This rise in white blood cells was mainly due to
increased numbers of circulating neutrophils (PMNL +68%) and
lymphocytes (+44%), whereas monocyte counts remained unchanged (Table
2).
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Adhesion molecules.
Numeric expression of 2-integrins (CD18/CD11b) on PMNL
was elevated after the end of the confinement period (Pre 110: 45.4 relative fluoresence units; Post 110: 53.4 relative fluoresence units;
Table 2).
O6 M)-stimulated production of O
Lymphocyte populations. The total number of circulating lymphocytes increased slightly after confinement but demonstrated no changes in the relative percentages of T and B cells and CD16/CD56-positive NK cells. After confinement, the percentages of the T-helper (CD3+CD4+) lymphocytes decreased, whereas suppressor (CD3+ CD8+) cells increased, respectively. As a result, the calculated CD4+/CD8+ ratio decreased slightly but not significantly (Pre 110: ~1.8, Post 110: ~1.5; Table 2).
Cytokines and CRP.
The plasma concentrations of IL-6 and INF- did not show any changes
and remained in the lower physiological range at all time points (IL-6)
or below the detection threshold (<0.1 pg/ml for INF-). The same
was true for CRP plasma concentrations (<0.01 mg/l; Table 2).
DTH. The DTH reaction to seven recall antigens injected intracutaneously was in the normal physiological range (>10 mm) for all subjects studied. Compared with Pre 110, a slight but not significant increase was observed Post 110 (see Table 5).
Group 240: Psychoneuroendocrine Changes
CST.
During confinement in group 240, the averaged CST scores
varied but remained in the normal physiological range, indicating no
stress. However, CST scores slightly increased again when confinement was finished (M6: 2.62 vs. Post 240: 2.96; Table
3).
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Cortisol. Physiological concentrations of morning and evening salivary cortisol were obtained before the confinement period (morning: ~16 nmol/l, evening: ~6 nmol/l), giving calculated m/e in the normal range (~3.5). This ratio did not change during the first months of confinement (M1-M3). Thereafter, the circadian rhythm of cortisol secretion was altered as verified by the reduction of m/e (M4: 1.4; M5: 2.0) but normalized during confinement (M6: 2.7, M7: 4.2). However, after confinement was finished the ratio visibly decreased again (Post 1.98; Table 3).
Prolactin. The concentration of prolactin was in the lower physiological range before confinement and increased after the onset of confinement and remained elevated throughout the entire observation period (Table 3).
Catecholamines. The basal (Pre 240) urine catecholamine excretion of dopamine, norepinephrine, and epinephrine (µg/24 h in pooled urine collected within 24 h) showed normal values in the lower physiological range. During confinement the urine excretion of norepinephrine first increased significantly (M1 vs. Pre 240, P < 0.05) but returned to basal norepinephrine values (M6, M7). After confinement was finished, norepinephrine concentration significantly increased, again (Post 240 vs. Pre, M2, M3, M4, M6, and M7; P < 0.05). The changes of dopamine exhibited the same kinetics but did not reach the level of significance. The low excretion of epinephrine did not change during the entire observation period (Table 3).
Group 240: Immunological Changes
Cell counts.
Determination of cell counts revealed an increase in the number of
circulating blood leukocytes from the second month onward (M2) until
the end of the confinement period (Post 240). The increase in the total
leukocyte count was mainly due to the significantly increased
concentrations of PMNL (M2, M3, and M4 vs. Pre 240; P < 0.05) and lymphocytes, whereas monocyte counts always remained low
(Table 4).
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Adhesion molecules.
Expression of 2-integrins showed slightly elevated, but
still physiological, values at Pre 240. 2-Integrins
further increased after the second month of confinement (M2) and
remained elevated throughout the confinement period (M6 vs. Pre,
P < 0.05; Table 4).
O
Lymphocyte populations. The total number of lymphocytes increased after confinement but still remained in the physiological range. No changes occured in the relative percentages of T and B cells, CD16/CD56-positive NK cells, CD3+CD4+ T-helper cells, and CD3+CD8+ T-suppressor cells throughout the confinement period.
However, at Post 240, the percentage of T lymphocytes decreased and the concentration of circulating CD3+CD4+ T-helper cells was reduced. Because CD3+CD8+ T-suppressor cells increased in all subjects, the ratio calculated between T-helper and T-suppressor cells was significantly reduced (Post 240 vs. M2, M3, M4, M6, and M7; P < 0.05; Table 4).Cytokines and CRP.
The plasma concentrations of the proinflammatory cytokines IL-6 and
INF- remained unchanged in the lower physiological range (IL-6) or
below the detection threshhold (<0.1 pg/ml for INF-). The same was
observed for CRP (Table 4).
DTH.
The determination of DTH revealed normal physiological values in all
subjects Pre 240 and Post 240 (Table 5).
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DISCUSSION |
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TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
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Previous studies in mice, sheep, and monkeys, as reviewed by Schmitt and Schaffar (28), already demonstrated a moderate role of isolation on neuroendocrinal and immunological functions. Because of the various and highly complex social interactions of humans, experimental conditions seem not to be fulfilled by animal models. The evaluation of the effects of confinement, especially during spaceflights, remains very important, because confinement in space may lead to psychic stress and to a compromised immune response in humans (15). The compromise of immune functions parallel to an increased probability of inflight infections may confirm the hypothesis that negative events (stress factors) can lead to negative emotional states (distress) that are related to changes in the innate part of the human immune system (11).
To systematically analyze the role of space-related factors with influence on the psychoneuroendocrine regulation and immunity, ground-based studies have already been carried out to simulate effects of long-term microgravity (24, 30) or confinement (10, 26). In a previous ground-based study mimicking reduced gravitation for 120 days by permanent bed rest (6° HDT), our laboratory observed substantial psychic stress, alterations of the circadian rhythm of cortisol secretion, an elevation of excretion of stress-permissive catecholamines (e.g., norepinephrine), and changes in cell counts and functions of immune cells in six subjects (5). These changes most likely reflect stimulation of the unspecific and the depression of the specific immune system by prolonged HDT (5).
On the basis of the results of the HDT study (5) and of the findings made by other groups in confinement studies (10, 26), we investigated in part the same variables in response to long-term confinement for 110 and 240 days in a space module, reflecting the conditions in a multimodule orbital station. True control groups (e.g., the same or a matched group of individuals subjected to daily life outside of the chamber for the same period of time), however, could not be studied. Because of the long-term approach of the present investigation, the same group of volunteers did not agree to undergo an additional experimental period of 110 or 240 days. This might also have had a "bias" effect on the subsequent experimental period that can only be overcome by a crossover design, which was not possible primarily because of financial reasons. To compensate the lack of a true control group, we compared the values obtained in the same subjects before confinement was started, representing an experimental design previously described (5, 24).
Confinement and Neuroendocrine Changes
Exposure to stress factors might influence the immune system due to the activation of the hypothalamo-pituitary-adrenal axis and the sympathoadrenergic response by elevated levels of stress-permissive hormones such as cortisol and catecholamines (6). The reliability of the determination of psychic stress by the CST was validated (21) and already applied in space research (30). Quantitative determination of salivary cortisol, serum prolactin, and urinary catecholamine excretion has also been shown to be a reliable method to assess stress-sensitive hormonal changes (2, 6, 13, 36).Pre vs. Post. In a comparison of the aforementioned parameters within each group (group 110 and group 240) before and after 110 and 240 days of confinement, respectively, it is obvious that psychic stress, as determined by the CST, did not develop to any significant extent, whereas confinement seems to affect the neuroendocrine response as suggested by the alterations in the circadian rhythm of cortisol secretion. Under physiological conditions, salivary cortisol levels show a circadian rhythm in three- to fivefold higher concentrations in the morning than in the evening (m/e), which was below 2 after confinement in both groups. Prolactin concentrations increased clearly after confinement. The excreted concentrations of dopamine and norepinephrine also increased significantly (Tables 1 and 3). Thus, although psychic stress was not detected by the CST, changes of secretion of cortisol, prolactin, and catecholamines demonstrated a neuroendocrine response at least after confinement in both groups.
During confinement. To determine whether these changes already occurred during the confinement period, additional saliva and urine samples were taken monthly during confinement in both groups.
In contrast to group 110, group 240 exhibited a slight increase of CST scores and a significantly elevated excretion of norepinephrine already in the first months of confinement. These changes showed a tendency to normal values in the sixth (M6) and seventh (M7) month. This was also observed for the diurnal secretion of cortisol, which was altered in the fourth and fifth months (m/e 1.4 or 2) but recovered thereafter (M6, M7). These effects might be due to the adaption of the individuals to the given living conditions, which were much more limited with respect to space and privacy in group 240. Thus the neuroendocrine consequences of long-term confinement appear to be initially dependent on the chamber space and privacy available for each subject. After longer periods of confinement (group 240), adaption may occur. Interestingly, return to normal life seems to be a very stressful event, irrespective of the time and conditions of confinement.Confinement and Immunological Changes
Pre vs. Post. The unspecific as well as the specific immune system play an essential role in protecting the body against microorganisms as the host's defense. Because no lymphoid tissue could be obtained, analyses of the immune system were merely based on samples of circulating blood cells and the interaction of specific and unspecific immune cells with intradermally injected standardized antigens by the DTH skin reaction.
The comparision of Pre to Post values of leukocyte and granulocyte counts and associated functional parameters suggests activation of the innate part of the immune system. Accordingly, the number of circulating PMNL was increased and the expression of2-integrins on PMNL was elevated. However, spontaneous
as well as fMLP-stimulated receptor-mediated O2-integrins), variables that reflect specific
immunity showed a minor depression. Although the total number of blood lymphocytes increased, the ratio of T-helper (CD3+
CD4+) to T-suppressor (CD3+CD8+)
lymphocytes decreased because of the increased number of
CD3+CD8+ lymphocytes.
To search for signs of possible functional consequences of neutrophil
activation and depression of the CD4+/CD8+
ratio of circulating lymphocytes, the DTH reaction was evaluated by a
standardized recall antigen multitest skin test (Immignost). This assay
can be performed repeatedly without sensibilization and with high
reproducibility (16). The skin reaction against intracutaneously administered antigens reflects an orchestrated group
of related responses to antigens that are essentially dependent on
CD4-positive lymphocytes, on various proinflammatory cytokines located
in the tissue, as well as on the activation of phagocytes as effector
cells. When CD4+ T-cell or phagocyte functions are
compromised, the entire sequence of cell-mediated responses is
affected, which hence results in an immunocompromised state
(4). A physiological reaction in men is defined as a mean
DTH erythema diameter >10 mm (3), which was observed
before and also after confinement in all subjects (Table 5). Thus the
slight depression of the CD4+/CD8+ ratio
appears to have no major effects on the functional state of the
specific cellular immunoreactivity against recall antigens in either
group 110 or group 240.
During confinement.
In group 240, additional blood samples were withdrawn
monthly (M1-M7), demonstrating an increase in the PMNL counts and
in the expression of 2-integrins already in the first
months of confinement. This activation seemed not to be due to an
inflammatory process, because other highly sensitive parameters of
systemic inflammation [e.g., concentrations of IL-6 (14,
22) and CRP (39)] remained very low at any time
point (Table 4). No changes in the specific part of the immune system
were observed during confinement. However, when subjects returned to
"normal" life the specific immune system appeared to be altered
because the ratio of T-helper to T-suppressor cells decreased (M7 ~ 2.3 vs. Post ~ 1.6). This was, however, without any effect
on the DTH.
Conclusions
The study presents the effects of long-term confinement for 110 and 240 days on Earth in working and living modules that are built to mimic the conditions on the ISS.During confinement for 110 days, subjects lived and worked in a
spacious chamber (200 m3). Under these conditions, no
psychoneuroendocrine stress response could be observed. In contrast,
when living and working space were reduced to almost half the size
(group 240), thereby leading to a lack of privacy, a chronic
stress response developed during confinement because of slightly
increased psychic stress, and alteration of the circadian rhythm of
cortisol secretion and prolactin plasma concentrations occurred. In
addition, excretion of catecholamines increased during the first months
after confinement but ceased thereafter, which might be due to
adaptation to the restricted living conditions. The innate part of the
immune response became activated, as suggested by the increase in the
number of PMNL and of the expression of 2-integrins,
whereas no enumerative changes occurred in lymphocyte subpopulations.
When confinement was terminated in both groups, parameters of psychic stress and sympathoadrenergic stimulation increased, reflecting a stressful readaption to normal life.
These Post confinement living conditions are supposed to have a strong impact on each individual. However, the changes in living conditions were comparable to those that are encountered by astronauts and cosmonauts on return to Earth. Like astronauts and cosmonauts, the volunteers subjected to confinement had to perform almost the same follow-up experiments and medical examinations. This return to "normality" obviously also affected the specific immune system, as proven by a decrease in the ratio of T-helper to T-suppressor cells in both groups. However, the decrease in CD4+ T cells did not alter the DTH.
Altogether, these results demonstrate moderate and distinct reactions of the neuroendocrine and immunological systems which from the laboratory point of view can be considered negative. Thus confinement caused changes of variables that reflect physiological rather than pathological adaptive processes. However, besides space-dependent environmental conditions, other variables like low gravitation and radiation may render astronauts and cosmonauts more sensitive to long-term confinement and social interactions occurring in a small group of humans living and working under hostile conditions.
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ACKNOWLEDGEMENTS |
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We thank Dr. M. Vogeser and G. Gröger for help and skillful assistance in the determination of catecholamines and cytokines and B. Lobstein for the revision of the manuscript.
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FOOTNOTES |
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This study was supported by Deutsche Agentur für Raumfahrtangelegenheiten Grant 50-WB992.
Some of this research was conducted by L. Smith in partial fulfillment of the requirements for a medical thesis from the Medical Faculty of the Ludwig-Maximilians-University of Munich (Munich, Germany).
Address for reprint requests and other correspondence: A. Choukèr, Clinic of Anaesthesiology, Ludwig-Maximilians-Univ. Munich, 81366 Munich, Germany (E-mail: alexander.chouker{at}ana.med.uni-muenchen.de).
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
10.1152/japplphysiol.00732.2001
Received 12 July 2001; accepted in final form 10 December 2001.
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REFERENCES |
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TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
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