Cytokine and chemokine mRNA expression by pDCs and cDCs isolated from MCMV-infected animals at 36 hours post-challenge. pDCs (red circles), CD8α cDCs (blue diamonds) and CD11b cDCs (green triangles) were purified from C57BL/6 mice injected with vehicle (open symbols) or infected with MCMV for 36 h (closed symbols). Pangenomic microarray experiments were performed with the total mRNA isolated from these cell populations [43] . The expression of mRNA (Y-axis, in arbitrary units in log10 scale) encoding various innate cytokines and chemokines (X-axis) in the three DC subsets studied is represented. Genes were classified in 5 groups accordingly to their pattern of expression across the 6 types of biological samples examined, using the GeneCluster software. Group 1 corresponds to the IFN-I genes which are undetectable or expressed only at very low level under steady state conditions, but which are induced to extremely high levels specifically in pDCs after infection. Group 2 corresponds to genes that are induced in all DC subsets but to a higher level in pDCs. Group 3 correspond to genes that are strongly induced to a comparable extent in all three DC subsets. Group 4 corresponds to genes induced to higher levels in cDCs as compared to pDCs. Group 5 corresponds to genes induced to higher levels specifically in CD8α cDCs.