Relative gene expression in nasal samples after S. suis intranasal inoculation. Log2 of the individual values and mean (black bars) of the relative gene expression in nasal samples 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) strains, and nasal swabs were taken at 4 h and 1, 2 and 3 days after inoculation. Genes showing significant difference (P < 0.05) in pairwise analysis 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. * P < 0.05 when comparing versus their respective 3 days before challenge time point. n = 8 for both strains at 4 h post-infection and 1 dpi, n = 4 for both strains at 2 and 3 dpi. IL1B 1 and IL1B 2 are both IL1B assays consisting of two different primer pairs targeting non-overlapping sites in the IL1B transcript. All expression values and significant differences can be found in Additional file 3.