Functional changes in neutrophils and psychoneuroendocrine responses during 105 days of confinement

The innate immune system as one key element of immunity and a prerequisite for an adequate host defense is of emerging interest in space research to ensure crew health and thus mission success. In ground-based studies, spaceflight-associated specifics such as confinement caused altered immune functions paralleled by changes in stress hormone levels. In this study, six men were confined for 105 days to a space module of ∼500 m3mimicking conditions of a long-term space mission. Psychic stress was surveyed by different questionnaires. Blood, saliva, and urine samples were taken before, during, and after confinement to determine quantitative and qualitative immune responses by analyzing enumerative assays and quantifying microbicide and phagocytic functions. Additionally, expression and shedding of L-selectin (CD62L) on granulocytes and different plasma cytokine levels were measured. Cortisol and catecholamine levels were analyzed in saliva and urine. Psychic stress or an activation of the psychoneuroendocrine system could not be testified. White blood cell counts were not significantly altered, but innate immune functions showed increased cytotoxic and reduced microbicide capabilities. Furthermore, a significantly enhanced shedding of CD62L might be a hint at increased migratory capabilities. However, this was observed in the absence of any acute inflammatory state, and no rise in plasma cytokine levels was detected. In summary, confinement for 105 days caused changes in innate immune functions. Whether these changes result from an alert immune state in preparation for further immune challenges or from a normal adaptive process during confinement remains to be clarified in future research.

520-d Isolation and confinement simulating a flight to Mars reveals heightened immune responses and alterations of leukocyte phenotype

During interplanetary exploration, chronic stress caused by long term isolation and confinement in the spacecraft is one of the major concerns of physical and psychological health of space travelers. And for human on Earth, more and more people live in an isolated condition, which has become a common social problem in modern western society. Collective evidences have indicated prolonged chronic stress could bring big influence to human immune function, which may lead to a variety of health problems. However, to what extent long-term isolation can affect the immune system still remains largely unknow. A simulated 520-d Mars mission provided an extraordinary chance to study the effect of prolonged isolation. Six healthy males participated in this mission and their active neuroendocrine and immune conditions were studied with saliva and blood samples from all participants on chosen time points during the isolation period. As a typical neuroendocrine parameter, stress hormone cortisol was measured in the morning saliva samples. Immune phenotype changes were monitored through peripheral leukocyte phenotype analysis. Using an ex vivo viral infection simulation assay we assessed the immune response changes characterized by the ability to produce representative endogenous pro-inflammatory cytokines. The results of this study revealed elevated cortisol levels, increased lymphocyte amount and heightened immune responses, suggesting that prolonged isolation acting as chronic stressors are able to trigger leukocyte phenotype changes and poorly controlled immune responses.

Cell-to-cell interactions in changed gravity: ground-based and flight experiments

Cell-to-cell interactions play an important role in all physiological processes and are mediated by humoral and mechanical factors. Mechanosensitive cells (e.g., osteocytes, chondrocytes, and fibroblasts) can be studied ex vivo to understand the effects of an altered gravity environment. In particular, cultured endothelial cells (EC) are very sensitive to a broad spectrum of mechanical and biochemical stimuli. Earlier, we demonstrated that clinorotation leads to cytoskeletal remodeling in cultured ECs. Long-term gravity vector changes also modulate the expression of surface adhesion molecules (ICAM-1, E-selectin, VCAM-1) on cultured ECs. To study the interactions of geterological cells, we cocultured endothelial monolayers and human lymphocytes, immune cells and myeloleucemic (K-560) cells. It was found that, although clinorotation did not alter the basal adhesion level of non-activated immune cells on endothelial monolayers, the adhesion of PMA-activated lymphocytes was increased. During flight experiments onboard the Russian segment of the International Space Station, we measured the cytotoxic activity of natural killer (NK) cells incubated with labeled target cells. It was found that immune cells in microgravity retained their ability to contact, recognize, and destroy oncogenic cells in vitro. Together, our data concerning the effects of simulated and real microgravity suggest that, despite changes in the cytoskeleton, cell motility, and expression of adhesion molecules, cell-cell interactions are not compromised, thus preserving the critical physiological functions of immune and endothelial cells.

Phagocyte system under spaceflight conditions

The spaceflight conditions lead to disturbances in immune system and cause the changes in microbial and chemical environment that create preconditions for immunodeficiency and allergic disease development. With the spaceflights lengthening the problem of crewmembers immunodeficiency and the probability of allergic disease manifestation became actual. The higher risk of various pathological conditions noted in cosmonauts during space flight due to lowered immunological resistance and unnatural biological and chemical environment (autoimmune reactions, bacterial and viral autoinfections, possible allergic events etc.) proves the need of studying the mechanisms of these disturbances and determination the most labile links between the immune system and antigen environment. In this case phagocytes seems to be one of the most important cells that can influence both induction and effector stage of immune reactions and also take part in the regulation of the immune response. The goal of the investigation was to conduct studies of one of the of the phagocytes metabolic and migration activity that are closely connected with functional activity of the cells.

Immune responses in extreme environments

In order to identify some of these interactions and regulation between the immune system and other physiological variables we have investigated the immune status in extreme conditions such as long term isolation and confinement, strict antiorthostatic bed rest and spaceflight.

Effect of SLS-2 spaceflight on immunologic parameters of rats

During the Spacelab Life Sciences-2 mission, rats were dissected in space and biosamples were returned to Earth for analysis. Immunologic studies addressed the kinetics of T lymphocyte proliferative responses, cytotoxic activity of natural killer cells, and cytokine production. Experiments were performed by using spleen and bone marrow of rats dissected before flight, during flight, immediately after landing of the space shuttle (R + 0), or 14 days after landing (R + 14), as well as those of respective control animals. Each group consisted of five male Sprague-Dawley rats. It was demonstrated that T lymphocyte activity of rats dissected in flight was significantly decreased compared with the controls. This was observed during 48-, 72-, and 96-h cultivation and stimulation with the following mitogenic stimuli: concanavalin A (Con A; 0.1, 1.0, and 10.0 mg/ml), phytohemagglutinin (PHA; 2.5 mg/ml), and interleukin-2 (IL-2; 1 U/ml). The cell proliferation rate in rats dissected immediately after landing did not decrease, whereas that in rats dissected at R + 14 increased. The activity of spleen natural killer cells was reduced in response to 51Cr-labeled target cells during flight (YAC-1 and K-562) and after flight (YAC-1). At R + 14, their activity returned to normal. Another technique employed to measure natural cytotoxicity, using [3H]uridine-labeled target cells and ribonuclease, did not reveal any differences between control and experimental groups. In bone marrow, the activity of natural killer cells did not vary significantly. The production of IL-1, IL-2, tumor necrosis factor (TNF)-alpha, and TNF-beta in spleen cell cultures of the flight rats was reduced. At R + 0, IL-1 and TNF-beta levels remained lowered, whereas TNF-alpha was increased. At R + 0, interferon-alpha and interferon-gamma levels were diminished. In summary, cell-mediated immunity in rats was significantly suppressed during flight. The time course variation of immune parameters after flight suggests that the changes may truly indicate a response of the immune system to spaceflight conditions that could increase over time.

The natural cytotoxicity in cosmonauts on board space stations

The nature of the changes of resistance to infection seems to be very important. Our studies indicate that different functions of natural killers could be depressed after the spaceflight. The decrease of the percentage of the lymphocytes that can bind target cells lead to the lowering of the "active" NK level and this can be resulted in the depression of total NK activity and lowering of resistance to viral and tumor antigens. The investigation of natural killer cells in cosmonauts before and after short and long- term spaceflights also revealed the important role of spaceflight duration, stress and individual immune reactivity.

Natural killer cells after ALTAIR mission

Reduced in vitro NK cytotoxic activity have routinely been observed after both prolonged and short-term space flights. This study investigated the effects of space flight on NK cell functions, NK cell counts and the production of IL-2 and TNF by lymphocytes of French-Russian crew members. In the French cosmonaut, after 21 days space flight, the cytotoxic activity of NK cells, the capacity the NK cells to bind and lyse the individual target cells and the percentage of NK cells were decreased. In this cosmonaut a twofold reduction TNF production in cultures of lymphocytes stimulated with PMA and with the mixture of PHA and PMA was observed on the first day after landing. However, the activity of the production of TNF in 48-hour PHA-cultures of lymphocytes was unchanged and the biological activity of IL-2 was not reduced. The immunological examination did not detect any substantial deviations from the norm in both russian cosmonauts after 197 days space flight. Various explanations for decreased cytotoxicity in cosmonauts after space flight can be proposed, and these include the defective function of NK cells and reduced numbers of circulating effector cells.

Results of space experiment program "Interferon"

The results of the biological space experiment "Interferon" performed by two international cosmonaut teams (26 May 1980, and 16 May 1981) aboard space laboratory Solyut-6 are reported: (1) Human lymphocytes separated from blood of healthy donors and placed into "Interferon I" equipment could be kept for 7 days in suspension culture under spaceflight conditions. Interferon production could be induced in human lymphocytes by preparations of different origin: virus, synthetic polyribonucleotides, bacterial protein and plant pigment. An increased lymphocyte interferon production in space laboratory compared to ground control was observed. (2) Human interferon preparations and interferon inducers placed in space laboratory at room temperature for 7 days maintained their biological activity. (3) A decrease of induced interferon production and natural killer activity of lymphocytes isolated from peripheral blood of cosmonauts was observed on the 1st day on Earth after 7-days spaceflight.