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.

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-κB 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.

Molecular characterization of Pleurodeles waltl activation-induced cytidine deaminase.

Activation-induced cytidine deaminase (AID) is involved in immunoglobulin affinity maturation, gene conversion and class switch recombination. This protein is therefore a major actor in the creation of the antibody repertoire. We have isolated, for the first time, the AID mRNA from a urodele amphibian, Pleurodeles waltl. This mRNA encodes 198 amino acids and shares 70% and 76% of similarity with Xenopus laevis and human AID sequences, respectively. All consensus motifs necessary for AID functions are present, suggesting that AID is functional in P. waltl. P. waltl AID is encoded by five exons as in other species. However, in contrast to mammalian AID, no splice variant could be detected in that species. We also noted that AID is predominantly expressed in the spleen, the major secondary lymphoid organ of P. waltl, and that the transcriptional regulation of P. waltl AID is partially different from that found in higher vertebrates. Furthermore, we showed that AID is expressed early during P. waltl embryonic development.

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.

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 spaceflight conditions.

A new isotype of immunoglobulin heavy chain in the urodele amphibian Pleurodeles waltl predominantly expressed in larvae.

Up to now, it was thought that urodele amphibians possessed only two IgH isotypes, IgM (mu) and IgY (upsilon). By screening a Pleurodeles waltl Ig cDNA mini-library, we identified three isotypes: IgM, IgY and a previously unknown class. IgM are multimeric molecules and represent the most abundant isotype throughout the life of P. waltl. IgY are likely the counterpart of mammalian IgA. The new isotype has typical Ig H-chain characteristics and is expressed as both secretory and membrane forms. Our analyses indicate that this isotype is restricted to Pleurodeles. Consequently, we named it "IgP" (pi) for Pleurodeles. This isotype is mainly expressed after hatching. Its expression decreases after metamorphosis. Our data indicate that IgP-expressing B cells present some similarities with mammalian B1-cells.