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

Özcan, Mine
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 to test this hypothesis, RNAs derived from two bona fide commensal bacteria, Lactobacillus salivarious, Lactobacillus fermentum, one commensal strain of Enterococcus faecium, one virulent clinical isolate of Enterococcus faecium and 2 strict pathogens, Listeria monocytogenes, Streptococcus pyogenes were used. The immunostimulatory activities of bacterial RNAs (bacRNA) were compared in in vitro and in vivo experiments. Human PBMCs, purified human neutrophils, and 2 distinct reporter cell lines stably expressing the endosomal ssRNA sensor TLR7 or the cytosolic sensors RIG-I and MDA-5 were stimulated with various doses of human commensal or pathogen-derived purified RNAs as such or following their complexation with the transfection reagent Lipofectamine 2000 or the anti-microbial peptide LL37. Since bacterial RNA was previously shown to be a signature of microbial vitality ( a VitaPAMP), we also tested the vaccine adjuvant activities of commensal versus pathogen derived bacRNAs in mice immunized with the model antigen OVA. The results indicate that commensal derived bacRNAs trigger a response dominated by Type I IFN production whereas those of pathogenic origin induce proinflammatory cytokine secretion that can also support Th1 development. Collectively, our findings suggest that commensals and pathogens may possess RNAs with sufficiently distinct structural features enabling their discrimination by immune cells.


Differential activation of immune cells by commensal versus pathogen-derived bacterial DNA
Günalp, Sinem; Gürsel, Mayda; Department of Biology (2015)
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 syst...
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...
Immunomodulatory effects of commensal bacteria-derived membrane vesicles
Alpdündar, Esin; Gürsel, Mayda; Department of Biology (2013)
Constitutive secretion of extracellular membrane vesicles is a common feature of cells from all domains of life including Archaea, Bacteria, and Eukarya. Although the contribution of gram negative bacterial outer membrane vesicles in disease pathogenesis has been extensively studied, whether commensal bacteria constitutively secrete such vesicles is still unknown. Given the importance of microbiota as regulators of immune homeostasis, we aimed to assess the immunomodulatory properties of extracellular vesic...
Differential immune activation following encapsulation of immunostimulatory CpG oligodeoxynucleotide in nanoliposomes.
Erikçi, E; Gürsel, Mayda; Gürsel, I (2011-02-01)
The immunogenicity of a vaccine formulation is closely related to the effective internalization by the innate immune cells that provide prolonged and simultaneous delivery of antigen and adjuvant to relevant antigen presenting cells. Endosome associated TLR9 recognizes microbial unmethylated CpG DNA. Clinical applications of TLR9 ligands are significantly hampered due to their pre-mature in vivo digestion and rapid clearance. Liposome encapsulation is a powerful tool to increase in vivo stability as well as...
Immune modulatory effects of pediococcus pentosaceus derived membrane vesicles: mechanism of action and therapeutic applications
Alpdündar Bulut, Esin; Gürsel, Mayda; Department of Biology (2018)
In our previous studies, we characterized 5 different human gram positive commensal bacteria derived membrane vesicles (MVs) and compared their activity with non-pathogenic E.coli derived membrane vesicles. Results showed that commensal bacteria derived MVs had immunomodulatory properties whereas non-pathogenic E.coli derived membrane vesicles had immune stimulatory properties. In this thesis, we aimed to focus our attention to Pediococcus pentosaceus-derived MVs that displayed the highest immunomodulatory ...
Citation Formats
M. Özcan, “Differential activation of immune cells by commensal versus pathogen-derived bacterial RNA,” M.S. - Master of Science, Middle East Technical University, 2014.