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

Thesis Type: Postgraduate

Institution Of The Thesis: Orta Doğu Teknik Üniversitesi, Faculty of Arts and Sciences, Department of Biology, Turkey

Approval Date: 2014


Consultant: MAYDA GÜRSEL


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.