Project description:Objective: It is unclear whether the host response of gram-positive sepsis differs from gram-negative sepsis at a transcriptome level. Using microarray technology, we compared the gene-expression profiles of gram-positive sepsis and gram-negative sepsis in critically ill patients. Design: A prospective cross-sectional study. Setting: A 20-bed general intensive care unit of a tertiary referral hospital. Patients: Seventy-two patients admitted to the intensive care unit. Interventions: Intravenous blood was collected for leukocyte separation and RNA extraction. Microarray experiements were then performed examing the expression level of 19,232 genes in each sample. Measurements and Main Results: There was no difference in the expression profile between gram-positive and gram-negative sepsis. The finding remained unchanged even when genes with lower expression level were included or after statistical stringency was lowered. There were, however, ninety-four genes differentially expressed between sepsis and control patients. These genes included those involved in immune regulation, inflammation and mitochondrial function. Hierarchical cluster analysis confirmed that the difference in gene expression profile existed between sepsis and control patients, but not between gram-positive and gram-negative patients. Conclusion: Gram-positive and gram-negative sepsis share a common host response at a transcriptome level. These findings support the hypothesis that the septic response is non-specific and is designed to provide a more general response that can be elicited by a wide range of different micro-organisms. The study included seventy-two critically ill patients admitted to the intensive care unit (ICU) of Nepean Hospital, Sydney, Australia. Of these, fifty-five patients were diagnosed to have sepsis, as confirmed by microbiological culture. The remaining seventeen patients did not have sepsis and were therefore used as controls. The study was approved by the hospital ethics committee and informed consent was obtained from all patients or their relatives. Patient Samples. Whole blood was taken from each patient on admission to ICU. Neutrophils were separated from whole blood using density-gradient separation with Ficoll-PaqueP P(Amersham). Subsequent neutrophil RNA extraction was performed using guanidinium thiocyanate (Ambion). Microarray Experiment. The neutrophil RNA was converted to cDNA, fluorescently labeled and hybridized to its complimentary sequences on the microarray (Invitrogen). The fluorescent signals on each micrroarray were captured using the GenePix 4000B laser scanner (Axon Instruments). Expression level of each gene was represented by the intensity of its fluorescent signal. Data Extraction. All signal intensity values were processed using background-subtraction method. Prior to analysis, all values were log-transformed and normalized by fitting a print-tip group Lowess curve. Normalization minimizes bias due to dye chemistry, signal intensity or location of a gene on the array. It ensures the detection of genes that are truly differentially expressed, instead of those caused by experimental artifacts or variation in the hybridization process. After normalization, genes that had more than 50% of data missing were removed. We then selected genes that had at least 80% of the data showing two-fold changes from the geneâs median values. After filtering, 1617 genes were available for further analysis.

Project description:Human newborns exhibit increased vulnerability and risk of mortality from infection. Increased susceptibility to infection during the neonatal period reflects key differences in the innate and adaptive immune responses relative to those in adult cells. We have previously shown an increase in the pleiotropic immune suppressive cytokine, IL-27, in macrophages derived from human umbilical cord blood compared with those obtained from adult peripheral blood. Similar findings exist in the neonatal murine system, as well as elevated splenic transcripts and serum levels. Recently, we established a murine model of neonatal sepsis to explore the impact of early life IL-27 levels on the host response to infection. In this model, neonatal mice deficient in IL-27 signaling exhibit reduced mortality, increased weight gain, and better control of the bacterial burden with reduced systemic inflammation. These results suggest that there is a reprogramming of the host response in the presence of IL-27 signaling. To explore this hypothesis, we profiled the neonatal transcriptome of the spleen in the presence or absence of Escherichia coli-induced sepsis in wild-type (WT) and IL-27Rα-deficient mice. The spleen, a known site of infection, exhibits increased IL-27 expression and bacterial burdens in WT pups that were significantly lower in IL-27Rα KO pups during infection. We identified 549 genes that were differentially expressed in WT neonates in response to E. coli infection. The upregulated genes were associated with inflammation, cytokine signaling, and G protein coupled receptor ligand binding and signaling. The expression level of these genes generally failed to increase in IL-27Rα KO mice upon the E. coli infection. We observed similar changes in gene expression, aligned with changes in chromatin accessibility, for macrophages isolated from the spleens of control and infected neonates with or without IL-27Rα KO, supporting macrophages as an innate myeloid population contributing to the inflammatory profile in septic WT pups. Collectively, our findings highlight a less inflammatory environment in KO pups that is not expected given the anti-inflammatory/suppressive activity of IL-27. However, it is consistent with a lower bacterial burden. This suggests that improved bacterial clearance in the absence of IL-27 signaling does not require a heightened inflammatory state, and instead, there is a direct relationship between IL-27 signaling and bacterial killing. An improved response to infection that is not reliant upon heightened levels of inflammation offers new promise to the potential of antagonizing IL-27 as a host-directed therapy for neonates without concern for driving inflammatory responses that are pathological to host tissues.

Dataset Information

Elevated Levels of Interleukin-27 in Early Life Compromise Protective Immunity in a Mouse Model of Gram-Negative Neonatal Sepsis.

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