Prokaryotic ribosomal RNA stimulates zebrafish embryonic innate immune system

Abhishikta Basu,Tamayo Uechi,Naoya Kenmochi,Maki Yoshihama

doi:10.1186/s13104-019-4878-8

Abstract

ObjectivesCell-culture studies reported that prokaryotic RNA molecules among the various microbe-associated molecular patterns (MAMPs) were uniquely present in live bacteria and were categorized as viability-associated MAMPs. They also reported that specific nucleotide modifications are instrumental in the discrimination between self and nonself RNAs. The aim of this study was to characterize the in vivo immune induction potential of prokaryotic and eukaryotic ribosomal RNAs (rRNAs) using zebrafish embryos as novel whole animal model system. Additionally, we aimed to test the possible role of rRNA modifications in immune recognition.ResultsWe used three immune markers to evaluate the induction potential of prokaryotic rRNA derived from Escherichia coli and eukaryotic rRNAs from chicken (nonself) and zebrafish (self). Lipopolysaccharide (LPS) of Pseudomonas aeruginosa served as a positive control. E. coli rRNA had an induction potential equivalent to that of LPS. The zebrafish innate immune system could discriminate between self and nonself rRNAs. Between the nonself rRNAs, E. coli rRNA was more immunogenic than chicken rRNA. The in vitro transcript of zebrafish 18S rRNA gene without the nucleotide modifications was not recognized by its own immune system. Our data suggested that prokaryotic rRNA is immunostimulatory in vivo and could be useful as an adjuvant.

Highlights

The recognition of microbe-associated molecular patterns (MAMPs) evokes the host innate immune system to induce downstream signaling pathways to eliminate the microbe
The zebrafish innate immune system could discriminate between self and nonself ribosomal RNA (rRNA)
Bacterial rRNA shows immunogenicity similar to LPS Embryos were injected at 30 hpf with various stimulants, and their induction potentials were compared at 2, 6 and 24 hpi by measuring the induced expression levels of il8, il1β and psmb9a genes

Summary

Introduction

The recognition of microbe-associated molecular patterns (MAMPs) evokes the host innate immune system to induce downstream signaling pathways to eliminate the microbe. Since the innate immune system can discriminate live microorganisms from dead ones via recognition of vita-MAMPs, studies on immunostimulation potential of vita-MAMPs have attracted attention in the fields of vaccines and adjuvants [1]. The immune response induced by bacterial RNA upon recognition includes NF-κB-dependent proinflammatory cytokines, type I. We introduced zebrafish embryos as whole animal model system to characterize the in vivo induction potential of self and nonself (prokaryotic and eukaryotic) rRNAs. In addition, we compared the induction potentials of the in vitro transcribed zebrafish 18S (IVT-18S) rRNA (devoid of any modifications) and native self rRNA to test the possible role of rRNA modifications in immune recognition. Zebrafish embryo is an attractive model system due to its small size, rapid life cycle, ex

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Conclusion