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Background: Clinical signs and symptoms of sepsis are nonspecific and often indistinguishable from those of nonseptic critical illness. This ambiguity frequently delays the diagnosis of sepsis until culture results can confirm the presence or absence of an infectious organism. Lymphocyte phenotyping can be conducted rapidly and may provide information on the presence of infection before culture results are available. In this study, we hypothesized that lymphocyte phenotype can distinguish between septic and nonseptic critical illness. Study Design: C57Bl/6 mice were subjected to either P aeruginosa pneumonia or lipopolysaccharide-induced acute lung injury (ALI). Animals were sacrificed 24 hours postinjury and splenic lymphocytes were harvested. Additionally, 13 patients in a surgical ICU were enrolled in the study. Whole blood was obtained and lymphocytes were isolated by density gradient centrifugation. Lymphocyte phenotype was identified through flow cytometry after labeling lymphocytes for CD3, CD4, CD8, CD20, CD40, CD69, and CD86 with fluorochrome-conjugated antibodies. Results: CD69 expression on B cells and CD8+ splenocytes from septic mice was significantly increased compared with acute lung injury mice (p < 0.001 and p < 0.05, respectively). Similarly, CD4+ and CD8+ lymphocytes from septic patients had a two- to threefold increase in the expression of CD69 compared with nonseptic critically ill patients (p < 0.05). Conclusions: These data indicated that CD69 expression on lymphocytes may be useful in distinguishing between septic and nonseptic critical illness. Continued investigation into the expression of CD69 during sepsis is warranted. [Copyright &y& Elsevier]

Background: Based on recent in vitro data, we tested the hypothesis that microarray expression profiles can be used to diagnose sepsis, distinguishing in vivo between sterile and infectious causes of systemic inflammation.Study Design: Exploratory studies were conducted using spleens from septic patients and from mice with abdominal sepsis. Seven patients with sepsis after injury were identified retrospectively and compared with six injured patients. C57BL/6 male mice were subjected to cecal ligation and puncture, or to IP lipopolysaccharide. Control mice had sham laparotomy or injection of IP saline, respectively. A sepsis classification model was created and tested on blood samples from septic mice.Results: Accuracy of sepsis prediction was obtained using cross-validation of gene expression data from 12 human spleen samples and from 16 mouse spleen samples. For blood studies, classifiers were constructed using data from a training data set of 26 microarrays. The error rate of the classifiers was estimated on seven de-identified microarrays, and then on a subsequent cross-validation for all 33 blood microarrays. Estimates of classification accuracy of sepsis in human spleen were 67.1%; in mouse spleen, 96%; and in mouse blood, 94.4% (all estimates were based on nested cross-validation). Lists of genes with substantial changes in expression between study and control groups were used to identify nine mouse common inflammatory response genes, six of which were mapped into a single pathway using contemporary pathway analysis tools.Conclusions: Sepsis induces changes in mouse leukocyte gene expression that can be used to diagnose sepsis apart from systemic inflammation. [ABSTRACT FROM AUTHOR]