Oligonucleotide and complementary DNA microarrays are being used to subclassify histologically similar tumours, monitor disease progress, and individualize treatment regimens. However, extracting new biological insight from high-throughput genomic studies of human diseases is a challenge, limited by difficulties in recognizing and evaluating relevant biological processes from huge quantities of experimental data. Here we present a structured network knowledge-base approach to analyse genome-wide transcriptional responses in the context of known functional interrelationships among proteins, small molecules and phenotypes. This approach was used to analyse changes in blood leukocyte gene expression patterns in human subjects receiving an inflammatory stimulus (bacterial endotoxin). We explore the known genome-wide interaction network to identify significant functional modules perturbed in response to this stimulus. Our analysis reveals that the human blood leukocyte response to acute systemic inflammation includes the transient dysregulation of leukocyte bioenergetics and modulation of translational machinery. These findings provide insight into the regulation of global leukocyte activities as they relate to innate immune system tolerance and increased susceptibility to infection in humans.

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Flagellin, the principal component of bacterial flagella, is a ligand for Toll-like receptor 5 (TLR5) or TLR11 and contributes to systemic inflammation during sepsis through activation of dendritic cells (DCs) and other cells of the innate immune system. Here, we report that flagellin and the TLR4 ligand, lipopolysaccharide (LPS), induced phenotypic and functional maturation of murine bone marrow-derived DCs and enhanced DC accumulation in the draining popliteal lymph node following their footpad injection. It is interesting that flagellin injection enhanced myeloid (CD8alpha(-1)) and plasmacytoid (plasmacytoid DC antigen(+) B220(+)) DC subsets, whereas LPS only increased myeloid DCs in the draining lymph node. In addition, the footpad injection of flagellin or LPS induced significant CD4(+) T cell activation in the draining popliteal lymph node, as judged by increased CD69 or CD25 expression. We illustrate, for the first time, that flagellin also increases natural killer (NK) cell number and activation status in the draining lymph node after footpad injection. Using coculture with enriched carboxy-fluorescein diacetate succinimidyl ester-labeled NK cells, flagellin-treated DCs induce significant NK cell proliferation and activation. In fact, direct treatment of NK cells with flagellin induces a greater increase in cell proliferation than treatment with LPS. In contrast, flagellin treatment of NK cells was not a strong inducer of interferon-gamma (IFN-gamma) production, indicating that NK cell proliferation and IFN-gamma production may be regulated differentially. These data suggest that flagellin is a capable maturation agent for murine myeloid-derived DCs, and flagellin-activated DCs and flagellin itself are potent inducers of NK cell proliferation.