The Megalocytivirus RBIV Induces Apoptosis and MHC Class I Presentation in Rock Bream (Oplegnathus fasciatus) Red Blood Cells

Abstract

Rock bream iridovirus (RBIV) causes severe mass mortality in Korean rock bream (Oplegnathus fasciatus) populations. To date, immune defense mechanisms of rock bream against RBIV are unclear. While red blood cells (RBCs) are known to be involved in the immune response against viral infections, the participation of rock bream RBCs in the immune response against RBIV has not been studied yet. In this study, we examined induction of the immune response in rock bream RBCs after RBIV infection. Each fish was injected with RBIV, and virus copy number in RBCs gradually increased from 4 days post-infection (dpi), peaking at 10 dpi. A total of 318 proteins were significantly regulated in RBCs from RBIV-infected individuals, 183 proteins were upregulated and 135 proteins were downregulated. Differentially upregulated proteins included those involved in cellular amino acid metabolic processes, cellular detoxification, snRNP assembly, and the spliceosome. Remarkably, the MHC class I-related protein pathway was upregulated during RBIV infection. Simultaneously, the regulation of apoptosis-related proteins, including caspase-6 (CASP6), caspase-9 (CASP9), Fas cell surface death receptor (FAS), desmoplakin (DSP), and p21 (RAC1)-activated kinase 2 (PAK2) changed with RBIV infection. Interestingly, the expression of genes within the ISG15 antiviral mechanism-related pathway, including filamin B (FLNB), interferon regulatory factor 3 (IRF3), nucleoporin 35 (NUP35), tripartite motif-containing 25 (TRIM25), and karyopherin subunit alpha 3 (KPNA3) were downregulated in RBCs from RBIV-infected individuals. Overall, these findings contribute to the understanding of RBIV pathogenesis and host interaction.

Co-Expression Network Analysis of Spleen Transcriptome in Rock Bream (Oplegnathus fasciatus) Naturally Infected with Rock Bream Iridovirus (RBIV)

“…It has been reported that caspase-3 is significantly up-regulated in the late phase of RBIV infection in the liver of rock bream [16]. Apoptosis-related proteins including CASP6, CASP9, and Fas in red blood cells were up-regulated in proteomic profiling [39]. Expression level of CASP3 in rock bream blood cells infected with RBIV is increased significantly at 6 hpi ( Figure 5B).…”

“…It is known that fish erythrocytes are involved in immune responses such as chemokine signaling pathway, platelet activation, and T cell receptor signaling pathway [38]. In proteome study of Jung et al [39], apoptosis-, MHC I-, and spliceosome-related pathways in rock bream RBCs were up-regulated, and antiviral mechanisms were down-regulated in the response to RBIV infection. In recent years, more evidence has emerged that platelet and their activation state can modulate innate and adaptive immune responses [40].…”

Aeromonas Hydrophila Infection Activates Death Receptor Apoptosis Pathway in the RBCs of Grass Carp (Ctenopharyngodon idellus)

“…The outcomes indicated that A. hydrophila infection could up-regulated four gene's expressions (P53, Fas, LRDD, and caspase 8) which were closely related with the death receptor apoptosis pathway, indicating that A. hydrophila infection could activate Fas-related death receptor apoptosis pathway. Interestingly, the Fas and caspase 9 genes of apoptosis-related pathways were the most over-expressed in RBCs of rock bream infected with a megalocytivirus [46].…”

Immune Functions of Erythrocytes in Osteichthyes

“…RBC apoptosis plays an important role also in the mechanism of antiviral immunity and inhibition of RBIV replication in infected fish O. fasciatus. Proteomic analysis of these cells showed an increase in expression of many proteins associated with the apoptosis pathway: CASP6 (caspase 6), CASP9 (caspase 9), and FAS (Fas cell surface death receptor) (16). Most likely, through their activity related to processing and presentation of antigen involving MHC I molecules and the pathway associated with apoptosis, these cells induce the activity of cytotoxic T cells (CD8 + ) and the release of perforin and granzyme, which are the main factors of the mechanism of cytotoxicity and apoptosis of an infected and antigen-presenting cell in the context of MHC I (16).…”

“…Moreover, erythrocytes of Osteichthyes are probably involved in the immune response as the antigen-presenting cells (APCs), via major histocompatibility complex (MHC) class II antigens, and they can contribute to formation of immune synapse with T cells and NK (natural killer) cells ( 15 ). In Osteichthyes, erythrocytes have been shown to participate in anti-infection immunity against viruses ( 4 , 6 , 9 – 11 , 16 , 17 ), bacteria ( 13 ), and fungi ( 18 ).…”