Figure 2

Principal component analysis (PCA) of 5,379 transcriptomic signatures of host responses to LPS assault mediated by different gravitational forces. The arrows indicate the shifts of the transcriptomic expressions due to LPS insults at two gravitational limits. The genes were mined by pair-wise comparison between the LPS-treated samples normalized by the untreated samples inoculated on ground and in spaceflight respectively; for instance, G-4 h and G-8 h were normalized by G-C and S-4 h and S-8 h were normalized by S-C. The close Euclidian proximity of the self-normalized G-C and S-C implies that variance profile of this PCA does not represent the exclusive impact of microgravity. A distant clustering between the LPS assault carried out on ground (G-4 h and G-8 h) and that carried out in spaceflight, S-4 h in particular, is marked by PC 1 explaining 80% of total variance. Thereby the impact of microgravity on LPS assault emerges as the most significant factor in explaining the genomic perturbation among these 5,379 genes. Modest Euclidian proximity between S-4 h and S-C (r = 0.16) suggests an immune blunting in spaceflight. Clearly, the host in spaceflight failed to respond to LPS assault. The position of S-8 h equidistant from the two clusters formed by (a) S-C, G-C and S-4 h and to (b) G-4 h and G-8 h suggests a delayed host response in spaceflight.