Relative gene expression in blood after S. suis intranasal inoculation. Log2 of the individual values and mean (black bars) of the relative gene expression in blood in S. suis inoculated piglets (gene expression was normalized relative to the 3 days before challenge mean for each inoculated group). Piglets were intranasally inoculated with S. suis T15 (non-virulent, blue bars) or S10 (virulent, red bars), and blood samples were taken at 4 h and 1, 2, and 3 days after inoculation. Genes with at least 1 significant difference in pairwise analysis (P < 0.05) when comparing different time points in the S. suis inoculated groups or between strains at the same time point, and with a mean greater than 2-fold change (log2 = 1) are shown. * indicates significant differences (P < 0.05) versus their respective 3 days before challenge time point. Differences between strains at the same time point are labelled with # (P < 0.05). n = 8 for both strains at 4 h post-infection and 1 dpi, n = 4 for both strains at 2 and 3 dpi. All expression values and significant differences can be found in Additional file 7.