Transcriptome Analysis of Paralichthys olivaceus Erythrocytes Reveals Profound Immune Responses Induced by Edwardsiella tarda Infection.

Bin Sun,Li Sun,Xuepeng Li,Xianhui Ning

doi:10.3390/ijms21093094

Abstract

Unlike mammalian red blood cells (RBCs), fish RBCs are nucleated and thus capable of gene expression. Japanese flounder (Paralichthys olivaceus) is a species of marine fish with important economic values. Flounder are susceptible to Edwardsiella tarda, a severe bacterial pathogen that is able to infect and survive in flounder phagocytes. However, the infectivity of and the immune response induced by E. tarda in flounder RBCs are unclear. In the present research, we found that E. tarda was able to invade and replicate inside flounder RBCs in both in vitro and in vivo infections. To investigate the immune response induced by E. tarda in RBCs, transcriptome analysis of the spleen RBCs of flounder challenged with E. tarda was performed. Six sequencing libraries were constructed, and an average of 43 million clean reads per library were obtained, with 85% of the reads being successfully mapped to the genome of flounder. A total of 1720 differentially expressed genes (DEGs) were identified in E. tarda-infected fish. The DEGs were significantly enriched in diverse Gene Ontology (GO) terms and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, especially those associated with immunity, disease, and infection. Ninety-one key DEGs involved in 12 immune-related pathways were found to form extensive interaction networks. Twenty-one genes that constituted the hub of the networks were further identified, which were highly regulated by E. tarda and involved in a number of immune processes, notably pathogen recognition and signal transduction, antigen processing and presentation, inflammation, and splicing. These results provide new insights into the immune role of flounder RBCs during bacterial infection.

Highlights

Red blood cells (RBCs) are the most abundant cell type in the blood
Nucleated red blood cells (RBCs) have been reported to be involved in various immune responses when stimulated with pathogens such as Escherichia coli [5], Candida albicans [6,7], infectious salmon anemia virus (ISAV) [8], piscine orthoreovirus (PRV) [2], non-replicating viruses like viral hemorrhagic septicemia virus (VHSV) [9], and infectious pancreatic necrosis virus (IPNV) [1,10]
Our previous study indicated that E. tarda could invade into flounder RBCs [27]

Summary

Introduction

Red blood cells (RBCs) are the most abundant cell type in the blood. While the mammalian mature RBCs lack nuclei, the RBCs of non-mammals contain nuclei and cytoplasmic organelles, which suggests the ability to synthesize proteins in response to stimuli [1,2,3,4]. Nucleated RBCs have been reported to be involved in various immune responses when stimulated with pathogens such as Escherichia coli [5], Candida albicans [6,7], infectious salmon anemia virus (ISAV) [8], piscine orthoreovirus (PRV) [2], non-replicating viruses like viral hemorrhagic septicemia virus (VHSV) [9], and infectious pancreatic necrosis virus (IPNV) [1,10]. The nucleated RBCs express pattern recognition receptors (PRRs) that recognize pathogen-associated molecular patterns (PAMPs) on microorganisms [11,12]. Rainbow trout and Atlantic salmon RBCs express Toll-like receptor (TLR) 3 and TLR9 that recognize. The MHC-I and MHC-II exposed on the surface of RBCs can be recognized by T cells and activate the adaptive immunity [12]

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Discussion

Conclusion