Though such studies are crucial for identifying stimulus specific effects, they are unable to account for the immunomodulatory effects of live bacteria, which frequently employ multiple survival strategies in parallel. Viable pathogenic bacteria secrete active components in the intercellular space and in the invaded cells in order to modulate the cellular response. In order to track the early events of gram-positive induced immune activation, we examined the total transcriptional response of isolated peripheral human CD14+/CD11b+ monocytes, infected with the viable

bacterial pathogens: Listeria monocytogenes, Staphylococcus aureus and Streptococcus pneumoniae (hereafter referred to as LM, SA Etomoxir concentration and SP respectively). All three pathogens belong to the

group of low GC content bacteria. SP and SA are leading pathogens in cases of gram-positive sepsis and LM is a cause of meningitis in immunocompromised patients and also sepsis in newborns. We designed and established a protocol enabling the detection of pathological changes early in the onset of infections with gram positive pathogens, before usual clinical parameters are upregulated, in an easily accessible cellular sample material. For these purposes, we focused our experimental analysis of naïve monocytes, which are easier to work with in ex vivo conditions than granulocytes, selleckchem even though they are represented in much lower numbers in vivo than the latter. Peripheral monocytes also are among the first members of the host immune system to encounter pathogens after injury and epithelial penetration. We limited the infection to a short interval of 1 hour in the attempt to mimic the in vivo early reaction of the cells after first encountering

the pathogen but before the onset of clinically manifested inflammation. Using microarray analysis, we were able to detect the transcriptional upregulation or repression of a robust minimal set of genes in infected cells compared to untreated controls in the short interval of one Aspartate hour. Despite donor specific gene variations and despite the different invasion strategies of the bacteria studied, we identified a common program of gene expression induced by all three bacterial pathogens. This program is characterized by the upregulation of a key cytokine – interleukin 23 (IL23). Results Global response pattern of peripheral monocytes to infection To assess the global response we performed clustering of the correlation coefficients of the entire gene expression matrix comprising the unchallenged and the infected monocytes with all three pathogens (Figure 1). This revealed an interesting pattern. As can be seen from the figure, there are three main clusters. Cluster A comprising the controls, Cluster B comprising infection with L. monocytogenes (LM) and S. aureus (SA), and Cluster C comprising infection with S. pneumoniae (SP).