Overview of differentially expressed genes in primed and challenged pbMEC (I.p.P.) compared to naïve cells challenged with the same E. coli stimuli (I.). A: Hierarchical clustering of the 226 DEGs comparing primed and challenged cells to naïve challenged pbMEC. The heat map represents the expression level of each DEG in the three different pbMEC preparations (1, 2, 3) as determined in the three challenge groups (I.p.P., I., and P.). Data were sorted according to the extent of the differential expression between I.p.P. vs. I. The heatmap is based on the log(2) fold changes between the 3 treatment groups relative to the respective un-stimulated control cells (Additional file 2, Table S2A). The rows of the matrix were normalized to have the values 0 as a mean, and 1 as associated variance. Red indicates high and green low expression. B: IPA network analysis of the regulatory relationship of DEGs between the treatment groups I.p.P. (induction post priming) vs I. (challenge of naïve cells). Red, higher expression in I.p.P.; green, lower expression in I.p.P. IL-1B is known to regulate the expression of 44 genes (red arrows). The transcription factor IRF7 is known to regulate the expression of 34 genes (blue arrows).