Transcriptomic signatures related to the immune priming of Ruditapes philippinarum in response to the re-infection of Vibrio anguillarum

Abstract

Manila clam (Ruditapes philippinarum) is a commercially valuable bivalve species, but its susceptibility to pathogenic microorganisms in aquaculture limits the development of the shellfish industry. Immune priming has been previously found in other invertebrates, but not in the unique immune system of the R. philippinarum. In the present study, the survival rate of R. philippinarum after two consecutive injections of Vibrio anguillarum was recorded, and the mechanisms of immune priming was studied by transcriptome analysis of R. philippinarum after two consecutive stimulations of V. anguillarum. R. philippinarum was first injected with V. anguillarum with PBS control group (SA), and then injected with V. anguillarum again after seven days (AA) with PBS control group (SS). The log-rank test showed that the survival rate of the AA group after the second injection was significantly higher than that of the other control groups (P < 0.05). The analysis of hepatopancreatic bacterial load showed that the pathogen clearance efficiency of the AA group was significantly enhanced. The activities of alkaline phosphatase (AKP), acid phosphatase (ACP), antioxidant enzymes (SOD) and malondialdehyde (MDA) were significantly increased after V. anguillarum infection, and the secondary stimulation was significantly higher than the primary stimulation. In addition, transcriptome analysis results showed that a common 84 differentially expressed genes (DEGs) were up-regulated after the primary stimulation and secondary stimulation compared with the SS control group, including C-type mannose receptor 2 (MRC2), Ubiquitin-like protein ATG12 (Atg12) and Toll-like receptor 4 (TLR4). The results of transcriptome analysis were verified by qRT-PCR of fifteen immune-related DEGs. The results showed that the pattern recognition receptors (PRR)-related genes are involved in immune priming. This study provides novel insights into physiological and molecular evidences of the immune priming response in R. philippinarum.