Effects of spaceflight on innate immune function and antioxidant gene expression

Abstract

Spaceflight conditions have a significant impact on a number of physiological functions due to psychological stress, radiation, and reduced gravity. To explore the effect of the flight environment on immunity, C57BL/6NTac mice were flown on a 13-day space shuttle mission (STS-118). In response to flight, animals had a reduction in liver, spleen, and thymus masses compared with ground (GRD) controls (P < 0.005). Splenic lymphocyte, monocyte/macrophage, and granulocyte counts were significantly reduced in the flight (FLT) mice (P < 0.05). Although spontaneous blastogenesis of splenocytes in FLT mice was increased, response to lipopolysaccharide (LPS), a B-cell mitogen derived from Escherichia coli, was decreased compared with GRD mice (P < 0.05). Secretion of IL-6 and IL-10, but not TNF-alpha, by LPS-stimulated splenocytes was increased in FLT mice (P < 0.05). Finally, many of the genes responsible for scavenging reactive oxygen species were upregulated after flight. These data indicate that exposure to the spaceflight environment can increase anti-inflammatory mechanisms and change the ex vivo response to LPS, a bacterial product associated with septic shock and a prominent Th1 response.

Fig. 1.

Effects of spaceflight on white blood cell (WBC) and major leukocyte population counts in spleen of flight (FLT) mice and ground (GRD) controls. Data were obtained with an automated hematology analyzer. Each bar represents mean ± SE (n = 12 mice /group). *P < 0.05; **P < 0.005; ***P < 0.001, GRD vs. FLT.

Fig. 2.

Effects of spaceflight on spontaneous and mitogen-induced blastogenesis in spleen. Data were obtained by quantifying the amount of tritiated thymidine ([³H]TdR) incorporated (cpm, counts per minute). Each bar represents mean ± SE (n = 12 mice /group). *P < 0.001, GRD vs. FLT.

Fig. 3.

Effects of spaceflight on cytokine secretion by activated splenocytes. Supernatants from splenocytes were obtained 48 h after incubation with LPS. Cytokine concentrations were evaluated using ELISAs. Each bar represents mean ± SE (n = 12 mice/group). *P < 0.05; **P < 0.001; ***P < 0.005, GRD vs. FLT.