Differential activation of immune cells by commensal versus pathogen-derived bacterial DNA

Günalp, Sinem
Immunological mechanisms making contribution to discriminating signals obtained from commensal versus pathogenic bacteria is an active area of research and recent evidence proposes that commensals and pathogens might express discrete variants of pathogen associated molecular patterns (PAMP). We hypothesized that as a major member of PAMP, bacterial DNA (bacDNA) originating from commensals versus pathogens might possess distinct immunostimulatory activities, enabling their dis- crimination by the immune system. To test this hypothesis, DNAs derived from two bona fide commensal bacteria, Lactobacillus fermentum, Lactobacillus salivarus, one commensal strain of Enterococcus faecium, one virulent clinical isolate of Enterococcus faecium and 2 strict pathogens; Listeria monocytogenes, Streptococcus pyogenes were used for human peripheral blood mononuclear cells, human neutrophils, murine splenocytes, murine fibroblasts, THP-1 monocytes, human (h)TLR9 expressing HEK cells, STING expressing and STING knockout interferon reporter cell lines were stimulated with various doses of human commensal or pathogen-derived purified DNAs as such or following their complexation with the transfection reagent Lipofectamine 2000. Results showed that commensal but not pathogen derived bacDNA induced IP-10 and IFN secretion from hPBMC. However, there was no significant difference in STING expressing B16 IFN-reporter cell line and murine fibroblast L929 cells. Almost 30-60% of the observed response was STING dependent. In contrast, DNAs derived from pathogens triggered significantly higher levels of TNF-α, IL-6 and/or IL-1 production from hPBMCs, human neutrophils and murine splenocytes. Consistent with this, NF-κB activation by hTLR9 expressing HEK cells was significantly higher upon stimulation with DNAs derived from pathogens. In conclusion, our findings suggest that pathogen and commensal bacterial DNAs are recognized by distinct sets of receptors and induce differential activation of immune cells. Collectively, commensal versus pathogen derived DNA’s route of entry into cells, their recognition by selective receptors /sensors and also their resistance to plasma nucleases might be important factors that contribute to such distinct responses.


Differential activation of immune cells by commensal versus pathogen-derived bacterial RNA
Özcan, Mine; Gürsel, Mayda; Department of Biology (2014)
Immunological mechanisms contributing to distinguishing signals derived from commensal versus pathogenic bacteria is an active area of research and recent evidence suggests that commensal and pathogens may express different variants of pathogen associated molecular patterns (PAMP). In this thesis, we propose that as a major member of PAMP, bacterial RNAs derived from commensal and pathogens may have distinct immunostimulatory activities due to differentially recognition by the host immune system. In order t...
Immunomodulatory activities of RNA species derived from commensal and pathogenic bacteria
Kayaoğlu, Başak; Gürsel, Mayda; Department of Biology (2017)
Bacterial RNAs are recognized by various types of immune sensors. Here, we aimed to investigate the differential immune activation mediated by RNAs purified from commensal or pathogenic bacteria. For this, total RNAs and/or individual ribosomal RNAs (5S, 16S and 23S) were isolated from two commensal bacteria, Lactobacillus salivarious and Lactobacillus fermentum and two pathogens, Listeria monocytogenes, and Streptococcus pyogenes. Bacterial RNA species isolated from pathogens induced stronger pro-inflammat...
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We describe a ribonucleic acid (RNA) reporter system for live-cell imaging of gene expression to detect changes in polymerase II activity on individual promoters in individual cells. The reporters use strings of RNA aptamers that constitute IMAGEtags (Intracellular MultiAptamer GEnetic tags) that can be expressed from a promoter of choice. For imaging, the cells are incubated with their ligands that are separately conjugated with one of the FRET pair, Cy3 and Cy5. The IMAGEtags were expressed in yeast from ...
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microRNA dependent gene expression regulation has roles in diverse processes such as differentiation, proliferation and apoptosis. Therefore, deregulated miRNA expression has functional importance for various diseases, including cancer. miR-125b is among the commonly downregulated miRNAs in breast cancer cells . Therefore we aimed to characterize the effects of miR-125b expression in MCF7 breast cancer cell line (BCCL) to better understand its roles in tumorigenesis. Here, we investigated mir-125 family mem...
Characterisation of immune responses in type I interferon associated diseases
Gül, Ersin; Gürsel, Mayda; Department of Biology (2016)
Type-I interferonopathies are a heterogeneous group of diseases arising from deregulation in nucleic acid sensing pathways, leading to constitutive type-I interferon release and pathology. DNA damage, if not repaired can also potentially activate such pathways. To test the hypothesis that 2 different DNA damage repair and immune deficiencies, Ataxia telangiectasia (AT) and Artemis deficiency could suffer from clinical manifestations associated with elevated type I IFN response, we compared the immune status...
Citation Formats
S. Günalp, “Differential activation of immune cells by commensal versus pathogen-derived bacterial DNA,” M.S. - Master of Science, Middle East Technical University, 2015.