Nathan Guéguinou

Could spaceflight-associated immune system weakening preclude the expansion of human presence beyond Earth’s orbit?

This year, we celebrate the 40th birthday of the first landing of humans on the moon. By 2020, astronauts should return to the lunar surface and establish an outpost there that will provide a technical basis for future manned missions to Mars. This paper summarizes major constraints associated with a trip to Mars, presents immunological hazards associated with this type of mission, and shows that our current understanding of the immunosuppressive effects of spaceflight is limited. Weakening of the immune system associated with spaceflight is therefore an area that should be considered more thoroughly before we undertake prolonged space voyages.

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.

Spaceflight-associated changes in immunoglobulin VH gene expression in the amphibian Pleurodeles waltl

Understanding why the immune system is depressed during spaceflight is of obvious importance for future human deep‐space missions, such as the foreseen missions to Mars. However, little is known about the effects of these flights on humoral immunity. We previously immunized adult Pleurodeles waltl (urodele amphibian) onboard the Mir space station and showed that heavy‐chain variable (VH) domains of specific IgM antibodies are encoded by genes belonging to the VHII and VHVI families. We have now determined how these animals use their individual VHII and VHVI genes by screening IgM heavy‐chain cDNA libraries and by quantifying IgM heavy‐chain transcripts encoded by these genes. Results were compared with those obtained using control animals immunized on Earth under the same conditions as onboard Mir. Our experiments revealed an increase in the expression of IgM heavy‐chain mRNAs encoded by the VHII and VHVI.C genes and a strong decrease in the expression of IgM heavy‐chain mRNAs encoded by the VHVI.A and VHVI.B genes in spaceflight animals. Consequently, different heavy‐chain mRNAs are expressed by spaceflight animals, demonstrating that this environment affects the humoral response. These observations may be due to a change in B‐cell selection under space flight conditions.— Bascove, M.,Huin‐Schohn, C., Gueguinou, N., Tschirhart, E., Frippiat, J.‐P. Spaceflight‐associated changes in immunoglobulin VH gene expression in the amphibian Pleurodeles waltl. FASEB J. 23, 1607–1615 (2009)

Decrease in antibody somatic hypermutation frequency under extreme, extended spaceflight conditions

Somatic hypermutation diversifies antibody binding sites by introducing point mutations in the variable domains of rearranged immunoglobulin genes. In this study, we analyzed somatic hypermutation in variable heavy‐chain (VH) domains of specific IgM antibodies of the urodele amphibian Pleurodeles waltl, immunized either on Earth or onboard the Mir space station. To detect somatic hypermutation, we aligned the variable domains of IgM heavy‐chain transcripts with the corresponding VH gene. We also quantified NF‐κPB and activation‐induced cytidine deaminase transcripts. Results were compared with those obtained using control animals immunized on Earth. Our data show that, as in most species of ectotherms, somatic hypermutation in P. waltl exhibits a mutational bias toward G and C bases. Furthermore, we show for the first time that somatic hypermutation occurs in space following immunization but at a lower frequency. This decrease is not due to a decrease in food intake or of the B‐cell receptor/antigen interaction or to the absence of the germinal center‐associated nuclear protein. It likely results from the combination of several spaceflight‐associated changes, such as the severe reduction in T‐cell activation, important perturbations of the cytoskeleton, and changes in the distribution of lymphocyte subpopulations and adhesion molecule expression.—Bascove, M., Guéguinou, N., Schaerlinger, B., Gauquelin‐Koch, G., Frippiat, J.‐P. Decrease in antibody somatic hypermutation frequency under extreme, extended spaceflight conditions. FASEB J. 25, 2947–2955 (2011). www.fasebj.org

Gravity changes during animal development affect IgM heavy-chain transcription and probably lymphopoiesis

Our previous research demonstrated that spaceflight conditions affect antibody production in response to an antigenic stimulation in adult amphibians. Here, we investigated whether antibody synthesis is affected when animal development occurs onboard a space station. To answer this question, embryos of the Iberian ribbed newt, Pleurodeles waltl, were sent to the International Space Station (ISS) before the initiation of immunoglobulin heavy‐chain expression. Thus, antibody synthesis began in space. On landing, we determined the effects of spaceflight on P. waltl development and IgM heavy‐chain transcription. Results were compared with those obtained using embryos that developed on Earth. We find that IgM heavy‐chain transcription is doubled at landing and that spaceflight does not affect P. waltl development and does not induce inflammation. We also recreated the environmental modifications encountered by the embryos during their development onboard the ISS. This strategy allowed us to demonstrate that gravity change is the factor responsible for antibody heavy‐chain transcription modifications that are associated with NF‐κB mRNA level variations. Taken together, and given that the larvae were not immunized, these data suggest a modification of lymphopoiesis when gravity changes occur during ontogeny.—Huin‐Schohn, C., Guéguinou, N., Schenten, V., Bascove, M., Koch, G. G., Baatout, S., Tschirhart, E., Frippiat, J.‐P. Gravity changes during animal development affect IgM heavy‐chain transcription and probably lymphopoiesis. FASEB J. 27, 333–341 (2013). www.fasebj.org

Modulation of Pleurodeles waltl DNA Polymerase mu Expression by Extreme Conditions Encountered during Spaceflight

DNA polymerase µ is involved in DNA repair, V(D)J recombination and likely somatic hypermutation of immunoglobulin genes. Our previous studies demonstrated that spaceflight conditions affect immunoglobulin gene expression and somatic hypermutation frequency. Consequently, we questioned whether Polμ expression could also be affected. To address this question, we characterized Polμ of the Iberian ribbed newt Pleurodeles waltl and exposed embryos of that species to spaceflight conditions or to environmental modifications corresponding to those encountered in the International Space Station. We noted a robust expression of Polμ mRNA during early ontogenesis and in the testis, suggesting that Polμ is involved in genomic stability. Full-length Polμ transcripts are 8–9 times more abundant in P. waltl than in humans and mice, thereby providing an explanation for the somatic hypermutation predilection of G and C bases in amphibians. Polμ transcription decreases after 10 days of development in space and radiation seem primarily involved in this down-regulation. However, space radiation, alone or in combination with a perturbation of the circadian rhythm, did not affect Polμ protein levels and did not induce protein oxidation, showing the limited impact of radiation encountered during a 10-day stay in the International Space Station.

Molecular cloning and expression analysis of Pleurodeles waltl complement component C3 under normal physiological conditions and environmental stresses.

C3 is a component of the complement system that plays a central role in immunity, development and tissue regeneration. In this study, we isolated the C3 cDNA of the Iberian ribbed newt Pleurodeles waltl. This cDNA encodes a 1637 amino acid protein with an estimated molecular mass of 212.5 kDa. The deduced amino acid sequence showed that P. waltl C3 contains all the conserved domains known to be critical for C3 function. Quantitative real-time PCR (qRT-PCR) demonstrated that under normal physiological conditions, P. waltl C3 mRNA is expressed early during development because it is likely required for neurulation. Then, its expression increased as the immune system developed. In adults, the liver is the richest source of C3, though other tissues can also contribute. Further analysis of C3 expression demonstrated that C3 transcription increased when P. waltl larvae were exposed to pH or temperature stress, suggesting that environmental modifications might affect this animals defenses against pathogens.

Pharmacological Countermeasures to Spaceflight-Induced Alterations of the Immune System

Opportunities for microbes to establish infections are enhanced under spaceflight conditions because space travel stimulates their growth (Chap. 15) and has a negative impact on immune functions. Indeed, it has been shown that spaceflight affects lymphoid organs (Gridley et al. 2003; Baqai et al. 2009) and induces variations in peripheral blood leukocyte subsets (Chap. 9). Neutrophil, monocyte, and NK cell functions are affected by spaceflight (Chaps. 10–12). The activation of T lymphocytes is also severely depressed under low gravity conditions (Cogoli et al. 1984) because interleukin-2 (IL-2) and IL-2receptor gene expression are modified, the delivery of the costimulatory signal to activate the B7/CD28 pathway and the protein kinase A (PKA) signaling pathway, which is a key early regulator in T cell activation, are hindered. Furthermore, a TH2 cytokine shift is associated with spaceflight. If this TH2 shift persists during long missions, it could represent a significant clinical risk for TH2-related autoimmune diseases, allergies, hypersensitivities, and disease susceptibility related to diminished cell-mediated immunity. Studies on plasma antibody levels did not reveal significant changes after short spaceflights (Rykova et al. 2008), but contradictory results were reported after long missions. Indeed, several studies (Konstantinova et al. 1993; Bascove et al. 2008, 2009; Gueguinou et al. 2009, 2010) reported increased levels of immunoglobulin while Rykova et al. (2008) reported normal amounts of antibodies after prolonged space missions. Lastly, a differential sensitivity of cellular and humoral immunity to spaceflight conditions seems to exist because it was shown that the cellular, but not the humoral, systems are affected by short periods of flight.