Effect of space flight on cytokine production and other immunologic parameters of rhesus monkeys

Short-Term Reloading After Prolonged Unloading Ensures Restoration of Stromal but Not Hematopoietic Precursor Activity in Tibia Bone Marrow of C57Bl/6N Mice

Bone and muscle tissues are mostly susceptible to different kinds of hypodynamia, including real and simulated microgravity (sμg). To evaluate the effect of sμg on bone marrow (BM), male C57Bl/6N mice were divided into three groups: vivarium control (VC), 30-day hindlimb suspension (HS), and subsequent 12-h short-term support reloading (RL). The effects on BM total mononucleated cells (MNCs) as well as stromal and hematopoietic progenitors from murine tibia were studied. The number of BM MNCs, immunophenotype, proliferation, colony-forming units (CFUs), differentiation and secretory activity of hematopoietic and stromal BM cells were determined. HS led to a twofold decrease in MNCs, alteration of surface molecule expression profiles, suppression of proliferative activity of BM cells, and change of soluble mediators' levels. The stromal compartment was characterized by a decrease of CFU of fibroblasts and suppression of spontaneous osteo-commitment after HS. Among the hematopoietic precursors, a decrease in the total number of CFUs was found mainly at the expense of suppression of CFU-GM and CFU-GEMM. After RL, restoration of the stromal precursor's functional activity to control levels and overabundance of paracrine mediator's production were detected, whereas the complete recovery of hematopoietic precursor's activity did not occur. These data demonstrate the fast functional reaction of the stromal compartment on restoration of loading support.

The Emerging Role of Macrophages in Immune System Dysfunction under Real and Simulated Microgravity Conditions

In the process of exploring space, the astronaut's body undergoes a series of physiological changes. At the level of cellular behavior, microgravity causes significant alterations, including bone loss, muscle atrophy, and cardiovascular deconditioning. At the level of gene expression, microgravity changes the expression of cytokines in many physiological processes, such as cell immunity, proliferation, and differentiation. At the level of signaling pathways, the mitogen-activated protein kinase (MAPK) signaling pathway participates in microgravity-induced immune malfunction. However, the mechanisms of these changes have not been fully elucidated. Recent studies suggest that the malfunction of macrophages is an important breakthrough for immune disorders in microgravity. As the first line of immune defense, macrophages play an essential role in maintaining homeostasis. They activate specific immune responses and participate in large numbers of physiological activities by presenting antigen and secreting cytokines. The purpose of this review is to summarize recent advances on the dysfunction of macrophages arisen from microgravity and to discuss the mechanisms of these abnormal responses. Hopefully, our work will contribute not only to the future exploration on the immune system in space, but also to the development of preventive and therapeutic drugs against the physiological consequences of spaceflight.

A Weakened Immune Response to Synthetic Exo-Peptides Predicts a Potential Biosecurity Risk in the Retrieval of Exo-Microorganisms

Simple Summary

We tested the immune response of T cells of the mammalian immune system towards protein antigens that includes the unusual amino acids isovaline and α-aminoisobutyric. Those amino acids have been found in high abundance on carbonaceous meteorites but are extremely rare in proteomes of earth organisms. We hypothesised that proteins of non-terrestrial alien life forms might contain such amino acids and tested whether chemically synthesised “exopeptides” that contain these amino acids could be detected by the immune system. Our assays, based on the responses of CD8⁺ T cells to these exopeptides, indicated that antigen cleavage, processing, and subsequent T cell activation still occurred, but were less efficient than the response to control peptides that lacked these amino acids. We therefore speculate that the encounter of putative exo-microorganisms of an unusual antigenic repertoire might pose an immunological risk for space missions aiming to retrieve potentially biotic samples from exoplanets and moons.

Abstract

The discovery of liquid water at several locations in the solar system raises the possibility that microbial life may have evolved outside Earth and as such could be accidently introduced into the Earth’s ecosystem. Unusual sugars or amino acids, like non-proteinogenic isovaline and α-aminoisobutyric acid that are vanishingly rare or absent from life forms on Earth, have been found in high abundance on non-terrestrial carbonaceous meteorites. It is therefore conceivable that exo-microorganisms might contain proteins that include these rare amino acids. We therefore asked whether the mammalian immune system would be able to recognize and induce appropriate immune responses to putative proteinaceous antigens that include these rare amino acids. To address this, we synthesised peptide antigens based on a backbone of ovalbumin and introduced isovaline and α-aminoisobutyric acid residues and demonstrated that these peptides can promote naïve OT-I cell activation and proliferation, but did so less efficiently than the canonical peptides. This is relevant to the biosecurity of missions that may retrieve samples from exoplanets and moons that have conditions that may be permissive for life, suggesting that accidental contamination and exposure to exo-microorganisms with such distinct proteomes might pose an immunological challenge.

Effects of High- and Low-LET Radiation on Human Hematopoietic System Reconstituted in Immunodeficient Mice

Over the last 50 years, a number of important physiological changes in humans who have traveled on spaceflights have been catalogued. Of major concern are the short- and long-term radiation-induced injuries to the hematopoietic system that may be induced by high-energy galactic cosmic rays encountered on interplanetary space missions. To collect data on the effects of space radiation on the human hematopoietic system in vivo, we used a humanized mouse model. In this study, we irradiated humanized mice with 0.4 Gy of 350 MeV/n ²⁸Si ions, a dose that has been shown to induce tumors in tumor-prone mice and a reference dose that has a relative biological effectiveness of 1 (1 Gy of 250-kVp X rays). Cell counts, cell subset frequency and cytogenetic data were collected from bone marrow spleen and blood of irradiated and control mice at short-term (7, 30 and 60 days) and long-term ( 6 - 7 months) time points postirradiation. The data show a significant short-term effect on the human hematopoietic stem cell counts imparted by both high- and low-LET radiation exposure. The radiation effects on bone marrow, spleen and blood human cell counts and human cell subset frequency were complex but did not alter the functions of the hematopoietic system. The long-term data acquired from high-LET irradiated mice showed complete recovery of the human hematopoietic system in all hematopoietic compartments. The combined results demonstrate that, in spite of early perturbation, the longer term effects of high-LET radiation are not detrimental to human hematopoiesis in our system of study.

Leukocyte activity is altered in a ground based murine model of microgravity and proton radiation exposure

Immune system adaptation during spaceflight is a concern in space medicine. Decreased circulating leukocytes observed during and after space flight infer suppressed immune responses and susceptibility to infection. The microgravity aspect of the space environment has been simulated on Earth to study adverse biological effects in astronauts. In this report, the hindlimb unloading (HU) model was employed to investigate the combined effects of solar particle event-like proton radiation and simulated microgravity on immune cell parameters including lymphocyte subtype populations and activity. Lymphocytes are a type of white blood cell critical for adaptive immune responses and T lymphocytes are regulators of cell-mediated immunity, controlling the entire immune response. Mice were suspended prior to and after proton radiation exposure (2 Gy dose) and total leukocyte numbers and splenic lymphocyte functionality were evaluated on days 4 or 21 after combined HU and radiation exposure. Total white blood cell (WBC), lymphocyte, neutrophil, and monocyte counts are reduced by approximately 65%, 70%, 55%, and 70%, respectively, compared to the non-treated control group at 4 days after combined exposure. Splenic lymphocyte subpopulations are altered at both time points investigated. At 21 days post-exposure to combined HU and proton radiation, T cell activation and proliferation were assessed in isolated lymphocytes. Cell surface expression of the Early Activation Marker, CD69, is decreased by 30% in the combined treatment group, compared to the non-treated control group and cell proliferation was suppressed by approximately 50%, compared to the non-treated control group. These findings reveal that the combined stressors (HU and proton radiation exposure) result in decreased leukocyte numbers and function, which could contribute to immune system dysfunction in crew members. This investigation is one of the first to report on combined proton radiation and simulated microgravity effects on hematopoietic, specifically immune cells.

Infection prevention and control during prolonged human space travel

Prolonged human spaceflight to another planet or an asteroid will introduce unique challenges of mitigating the risk of infection. During space travel, exposure to microgravity, radiation, and stress alter human immunoregulatory responses, which can in turn impact an astronaut's ability to prevent acquisition of infectious agents or reactivation of latent infection. In addition, microgravity affects virulence, growth kinetics, and biofilm formation of potential microbial pathogens. These interactions occur in a confined space in microgravity, providing ample opportunity for heavy microbial contamination of the environment. In addition, there is the persistence of aerosolized, microbe-containing particles. Any mission involving prolonged human spaceflight must be carefully planned to minimize vulnerabilities and maximize the likelihood of success.

Stress response and humoral immune system alterations related to chronic hypergravity in mice

Spaceflights are known to induce stress and immune dysregulation. Centrifugation, as hindlimb unloading, is a good ground based-model to simulate altered gravity which occurs during space missions. The aim of this study was to investigate the consequences of a long-term exposure to different levels of hypergravity on the stress response and the humoral immunity in a mouse model. For this purpose, adult C57Bl/6J male mice were subjected for 21 days either to control conditions or to 2G or 3G acceleration gravity forces. Corticosterone level and anxiety behavior revealed a stress response which was associated with a decrease of body weight, after 21-day of centrifugation at 3G but not at 2G. Spleen lymphocyte lipopolysaccharide (LPS) responsiveness was diminished by 40% in the 2G group only, whereas a decrease was noted when cells were stimulated with concanavalin A for both 2G and 3G groups (about 25% and 20%, respectively) compared to controls. Pro-inflammatory chemokines (MCP-1 and IP-10) and Th1 cytokines (IFNγ and IL2) were slightly decreased in the 2G group and strongly decreased in the 3G mouse group. Regarding Th2 cytokines (IL4, IL5) no further significant modification was observed, whereas the immunosuppressive cytokine IL10 was slightly increased in the 3G mice. Finally, serum IgG concentration was twice higher whereas IgA concentration was slightly increased (about 30%) and IgM were unchanged in 2G mice compared to controls. No difference was observed in the 3G group with these isotypes. Consequently, functional immune dysregulations and stress responses were dependent of the gravity level.

Immune system changes during simulated planetary exploration on Devon Island, high arctic

Background

Dysregulation of the immune system has been shown to occur during spaceflight, although the detailed nature of the phenomenon and the clinical risks for exploration class missions have yet to be established. Also, the growing clinical significance of immune system evaluation combined with epidemic infectious disease rates in third world countries provides a strong rationale for the development of field-compatible clinical immunology techniques and equipment. In July 2002 NASA performed a comprehensive immune assessment on field team members participating in the Haughton-Mars Project (HMP) on Devon Island in the high Canadian Arctic. The purpose of the study was to evaluate the effect of mission-associated stressors on the human immune system. To perform the study, the development of techniques for processing immune samples in remote field locations was required. Ten HMP-2002 participants volunteered for the study. A field protocol was developed at NASA-JSC for performing sample collection, blood staining/processing for immunophenotype analysis, whole-blood mitogenic culture for functional assessments and cell-sample preservation on-location at Devon Island. Specific assays included peripheral leukocyte distribution; constitutively activated T cells, intracellular cytokine profiles, plasma cortisol and EBV viral antibody levels. Study timepoints were 30 days prior to mission start, mid-mission and 60 days after mission completion.

Results

The protocol developed for immune sample processing in remote field locations functioned properly. Samples were processed on Devon Island, and stabilized for subsequent analysis at the Johnson Space Center in Houston. The data indicated that some phenotype, immune function and stress hormone changes occurred in the HMP field participants that were largely distinct from pre-mission baseline and post-mission recovery data. These immune changes appear similar to those observed in astronauts following spaceflight.

Conclusion

The immune system changes described during the HMP field deployment validate the use of the HMP as a ground-based spaceflight/planetary exploration analog for some aspects of human physiology. The sample processing protocol developed for this study may have applications for immune studies in remote terrestrial field locations. Elements of this protocol could possibly be adapted for future in-flight immunology studies conducted during space missions.

Considerations for non-invasive in-flight monitoring of astronaut immune status with potential use of MEMS and NEMS devices

The dynamics of how astronauts' immune systems respond to space flight have been studied extensively, but the complex process has not to date been thoroughly characterized, nor have the underlying principles of what causes the immune system to change in microgravity been fully determined. Statistically significant results regarding overall immunological effects in space have not yet been established due to the relatively limited amount of experimental data available, and are further complicated by the findings not showing systematically reproducible trends. Collecting in vivo data during flight without affecting the system being measured would increase understanding of the immune response process. The aims of this paper are to briefly review the current knowledge regarding how the immune system is altered in space flight; to present a group of candidate biomarkers that could be useful for in-flight monitoring and give an overview of the current methods used to measure these markers; and finally, to further establish the need and usefulness of incorporating real-time analytical techniques for in-flight assessment of astronaut health, emphasizing the potential application of MEMS/NEMS devices.

Mouse infection models for space flight immunology

Several immunological processes can be affected by space flight. However, there is little evidence to suggest that flight-induced immunological deficits lead to illness. Therefore, one of our goals has been to define models to examine host resistance during space flight. Our working hypothesis is that space flight crews will come from a heterogeneous population; the immune response gene make-up will be quite varied. It is unknown how much the immune response gene variation contributes to the potential threat from infectious organisms, allergic responses or other long term health problems (e.g. cancer). This article details recent efforts of the Kansas State University gravitational immunology group to assess how population heterogeneity impacts host health, either in laboratory experimental situations and/or using the skeletal unloading model of space-flight stress. This paper details our use of several mouse strains with several different genotypes. In particular, mice with varying MHCII allotypes and mice on the C57BL background with different genetic defects have been particularly useful tools with which to study infections by Staphylococcus aureus, Salmonella typhimurium, Pasteurella pneumotropica and Ehrlichia chaffeensis. We propose that some of these experimental challenge models will be useful to assess the effects of space flight on host resistance to infection.

Altered cytokine expression in tissues of mice subjected to simulated microgravity

Space flight is known to induce microgravity-associated immune dysfunction in humans, non-human primates and rodents. To understand the mechanism underlying these defects, several studies in rodents have been conducted in a ground-based antiorthostatic suspension (AOS) model that would mimic the effects of microgravity. In all these in vivo studies that showed the effects on cytokine profiles actually investigated the ex vivo production from culturing the cells isolated from whole organism that was exposed to space flight and/or microgravity. So, the purpose of the study was to examine the in vivo expression of cytokines in mice in immunologically important tissue environments of mice that were subjected to AOS. Cytokines such as Interleukin-1beta, (IL-1beta), IL-2, IL-3, IL-6, Interferon-gamma (IFN-gamma) and Tumor Necrosis Factor-alpha (TNF-alpha) were measured by Enzyme Linked Immunosorbent Assay (ELISA) in the homogenates of spleen tissue, lymph nodes and also in serum of AOS mice and compared with that of control mice. AOS induced no change in the IL-3 levels, but IL-1beta was increased significantly whereas IL-2 levels decreased in spleen, lymph nodes and serum. IL-6 levels did not differ in spleen but were significantly increased in lymph nodes and serum of AOS mice. IFN-gamma levels in spleen did not change but showed nonsignificant reduction in lymph nodes and significant reduction in serum in response to AOS. TNF-alpha levels in spleen and serum were unchanged and increased in lymph nodes. This in vivo cytokine study confirms the earlier findings that microgravity-simulated conditions induce tissue-specific immune response.

Animal models for the study of the effects of spaceflight on the immune system

Animal models have been used to determine the effects of spaceflight on the immune system. Rats and rhesus monkeys have been the primary animals used for actual space flight studies, but mice have also been utilized for studies in ground-based models. The primary ground based model used has been hindlimb unloading of rodents, which is similar to the chronic bed-rest model for humans. A variety of immune responses have been shown to be modified when animals are hindlimb unloaded. These results parallel those observed when animals are flown in space. In general, immune responses are depressed in animals maintained in the hindlimb unloading model or flown in space. These results raise the possibility that spaceflight could result in decreased resistance to infection in animals.

The immune system in space and microgravity

Space flight and models that created conditions similar to those that occur during space flight have been shown to affect a variety of immunological responses. These have primarily been cell-mediated immune responses including leukocyte proliferation, cytokine production, and leukocyte subset distribution. The mechanisms and biomedical consequences of these changes remain to be established. Among the possible causes of space flight-induced alterations in immune responses are exposure to microgravity, exposure to stress, exposure to radiation, and many more as yet undetermined causes. This review chronicles the known effects of space flight on the immune system and explores the possible role of stress in contributing to these changes.

Immune function during space flight

It is very likely that the human immune system will be altered in astronauts exposed to the conditions of long-term space flight: isolation, containment, microgravity, radiation, microbial contamination, sleep disruption, and insufficient nutrition. In human and animal subjects flown in space, there is evidence of immune compromise, reactivation of latent virus infection, and possible development of a premalignant or malignant condition. Moreover, in ground-based space flight model investigations, there is evidence of immune compromise and reactivation of latent virus infection. All of these observations in space flight itself or in ground-based models of space flight have a strong resonance in a wealth of human pathologic conditions involving the immune system where reactivated virus infections and cancer appear as natural consequences. The clinical conditions of Epstein-Barr-driven lymphomas in transplant patients and Kaposi's sarcoma in patients with autoimmune deficiency virus come easily to mind in trying to identify these conditions. With these thoughts in mind, it is highly appropriate, indeed imperative, that careful investigations of human immunity, infection, and cancer be made by space flight researchers.

Dietary nucleotides prevent decrease in cellular immunity in ground-based microgravity analog

Microgravity and stress of spaceflights result in immune dysfunction. The role of nutrition, especially nucleotide supplementation, has become an area of intensive research and significant interest in immunomodulation for maintenance of cellular immune responses. The studies presented here evaluate the plausibility of administering nucleotides to obviate immune dysfunction in an Earth-based in vivo analog of microgravity as studied in anti-orthostatic tail suspension (AOS) of mice. Mice were divided into three housing groups: group, isolation, and AOS. Mice were fed either control chow diet (CD), or RNA-, adenine-, or uracil-supplemented CD for the 1-wk duration of the experiments. In AOS mice, supplemental nucleotides significantly increased in vivo lymph node proliferation and ex vivo lymphoproliferation response to alloantigen and mitogens, respectively, and interleukin-2 and interferon-gamma production. A lower corticosterone level was observed in uracil-supplemented CD compared with CD. These results suggest that exogenous nucleotide supplementation, especially uracil, of normal diet is beneficial in the maintenance and restoration of the immune response during the microgravity analog conditions.

Suppression of human anti-inflammatory plasma cytokines IL-10 and IL-1RA with elevation of proinflammatory cytokine IFN-gamma during the isolation of the Antarctic winter

Cellular immune function has been shown to be decreased and latent virus shedding to be increased in human beings isolated during the Antarctic winter, a model used for assessing some effects of space flight. However, the balance of proinflammatory (IFN-gamma) and anti-inflammatory (IL-10 and IL-1RA) cytokines has not previously been evaluated. We therefore sought to determine whether isolation during the Antarctic winter would alter the proinflammatory and anti-inflammatory cytokine balance. Cytokine levels were measured with ELISA in monthly plasma samples from January through September 1999 in 21 study subjects in the Antarctic and 7 control subjects on Macquarie Island. There was a significant time-dependent increase in plasma IFN-gamma (P =.039) as well as decreases in IL-10 (P =.042) and IL-1RA (P =.053) in the study subjects compared with the control subjects. The study subjects also had significantly increased plasma IFN-gamma levels (P < or =.045) but decreased IL-10 and IL-1RA levels (P < or =.036) at individual time points of isolation. Isolation of human beings in the Antarctic appears to shift the plasma cytokine balance toward a proinflammatory profile. These observations are consistent with T-cell activation that might be due to activation of latent viruses, and they could hold importance for determining the risks of space flight.

Characteristics of human dendritic cells generated in a microgravity analog culture system

Generation of an effective immune response requires that antigens be processed and presented to T lymphocytes by antigen-presenting cells, the most efficient of which are dendritic cells (DC). Because of their influence on both the innate and the acquired arms of immunity, a defect in DC would be expected to result in a broad impairment of immune function, not unlike that observed in astronauts during or after space flight. In the study reported here, we investigated whether DC generation and function are altered in a culture environment that models microgravity, i.e., the rotary-cell culture system (RCCS). We observed that RCCS supported the generation of DC identified by morphology, phenotype (HLA-DR+ and lacking lineage-associated markers), and function (high allostimulatory activity). However, the yield of DC from RCCS was significantly lower than that from static cultures. RCCS-generated DC were less able to phagocytose Aspergillus fumigatus conidia and expressed a lower density of surface HLA-DR. The proportion of DC expressing CD80 was also significantly reduced in RCCS compared to static cultures. When exposed to fungal antigens, RCCS-generated DC produced lower levels of interleukin-12 and failed to upregulate some costimulatory/adhesion molecules involved in antigen presentation. These data suggest that DC generation, and some functions needed to mount an effective immune response to pathogens, may be disturbed in the microgravity environment of space.

Effects of spaceflight and PEG-IL-2 on rat physiological and immunological responses

Sprague-Dawley rats were subjected to two 8-day spaceflights on the space shuttle. Rats housed in the National Aeronautics and Space Administration's animal enclosure were injected (iv or sc) with pegylated interleukin-2 (PEG-IL-2) or a placebo. We tested the hypothesis that PEG-IL-2 would ameliorate some of the effects of spaceflight. We measured body and organ weights; blood cell differentials; plasma corticosterone; colony-forming units (macrophage and granulocyte macrophage); lymphocyte mitogenic, superantigenic, and interferon-gamma responses; bone marrow cell and peritoneal macrophage cytokine secretion; and bone strength and mass. Few immunological parameters were affected by spaceflight. However, some spaceflight effects were observed in each flight. Specifically, peritoneal macrophage spontaneous secretion of tumor necrosis factor-alpha occurred in the first but not in the second flight. A significant monocytopenia and lymphocytopenia were detected in the second but not in the first flight. The second mission produced bone changes more consistent with past spaceflight investigations. PEG-IL-2 did not appear to be beneficial; however, this was mostly due to the lack of spaceflight effects. These studies reflect the difficulty in reproducing experimental models by using current space shuttle conditions.

Effects of space flight on surface marker expression

Space flight has been shown to affect expression of several cell surface markers. These markers play important roles in regulation of immune responses, including CD4 and CD8. The studies have involved flight of experimental animals and humans followed by analysis of tissue samples (blood in humans, rats and monkeys, spleen, thymus, lymph nodes and bone marrow in rodents). The degree and direction of the changes induced by space flight have been determined by the conditions of the flight. Also, there may be compartmentalization of the response of surface markers to space flight, with differences in the response of cells isolated from blood and local immune tissue. The same type of compartmentalization was also observed with cell adhesion molecules (integrins). In this case, the expression of integrins from lymph node cells differed from that of splenocytes isolated from rats immediately after space flight. Cell culture studies have indicated that there may be an inhibition in conversion of a precursor cell line to cells exhibiting mature macrophage characteristics after space flight, however, these experiments were limited as a result of technical difficulties. In general, it is clear that space flight results in alterations of cell surface markers. The biological significance of these changes remains to be established.

Space flight, microgravity, stress, and immune responses

Exposure of animals and humans to space flight conditions has resulted in numerous alterations in immunological parameters. Decreases in lymphocyte blastogenesis, cytokine production, and natural killer cell activity have all been reported after space flight. Alterations in leukocyte subset distribution have also been reported after flight of humans and animals in space. The relative contribution of microgravity conditions and stress to the observed results has not been established. Antiorthostatic, hypokinetic, hypodynamic, suspension of rodents and chronic head-down tilt bed-rest of humans have been used to model effects of microgravity on immune responses. After use of these models, some effects of space flight on immune responses, such as decreases in cytokine function, were observed, but others, such as alterations in leukocyte subset distribution, were not observed. These results suggest that stresses that occur during space flight could combine with microgravity conditions in inducing the changes seen in immune responses after space flight. The biological/biomedical significance of space flight induced changes in immune parameters remains to be established. Grant Numbers: NCC2-859, NAG2-933.

Spaceflight and development of immune responses

The NIH.R1 Space Shuttle experiment was designed to study the effects of spaceflight on rodent development. Pregnant rats were flown on the Space Shuttle for 11 days, and pregnant control rats were maintained in animal enclosure modules in a ground-based chamber under conditions approximating those in flight. Additional controls were in standard housing. The effects of the flight on immunological parameters of dams, fetuses, and pups were determined. Blastogenesis of spleen cells in response to mitogen was inhibited in flown dams but was not inhibited in cells from their pups. Interferon-gamma production by spleen cells showed a trend toward inhibition in flown dams but not in their pups. The response of bone marrow cells to colony-stimulating factor showed a trend toward inhibition after spaceflight in dams, but the response of fetus and pup liver cells was not inhibited. Total serum IgG was not affected by spaceflight. None of the examined immune parameters that were altered in rat dams after spaceflight was found to be altered in their offspring.