Response of chemokine receptors CXCR2 and integrin β2 after Streptococcus agalactiae and Aeromonas hydrophila challenge in GIFT strain of Nile tilapia Oreochromis niloticus

Genome-wide characterization of integrin (ITG) gene family and their expression profiling in half-smooth tongue sole (Cynoglossus semilaevis) upon Vibrio anguillarum infection

Integrins (ITGs) are transmembrane heterodimer receptors with ITGα subunit and ITGβ subunit, participating in various physiological processes, including immunity. At present, systematic research on ITGs in teleost is scarce, especially in half-smooth tongue sole (Cynoglossus semilaevis). In this study, a set of 28 ITG genes in half-smooth tongue sole have been identified and characterized. The phylogenetic analysis showed that ITGα and ITGβ subunits were respectively classified into five and two clusters, consistent with previous studies. The selection pressure analysis indicated that most of ITG genes were under purifying selection, except for ITGα11b and ITGαL with positive selection. The expression profiles of eight selected ITG genes, including ITGα1, ITGα5, ITGα8, ITGα11, ITGβ1, ITGβ2, ITGβ3, and ITGβ8, were analyzed in healthy tissues and after infection with Vibrio anguillarum, revealed their implications in immune response. The study provided a comprehensive characterization and expression analysis of ITG genes in half-smooth tongue sole, setting a solid foundation for further functional studies and promising potential in disease control.

Functional and expression analysis reveals the involvement of integrin αvβ3 in antiviral immunity of grass carp (Ctenopharyngodon idella)

Integrins are α-β heterodimeric cell receptors that can bind the protein components of pathogens, and play crucial roles in mammalian immune responses, but the immune functions mediated by integrins remains largely unknown in teleost fish. In this study, an integrin αvβ3 (GCαvβ3) originally assembled by αv (GCαv) and β3 (GCβ3) subunits, was identified from a teleost fish grass carp Ctenopharyngodon idella. The pairwise alignment analyses showed that the amino acid sequences of GCαv and GCβ3 shared high similarity (75.2-95.1%) and identity (58.6-90.7%) with their homologs from other vertebrates. Both GCαv and GCβ3 harbored the conserved protein domains and motifs, and were clustered in fish branch of the phylogenetic tree containing the counterparts from various vertebrates. Co-immunoprecipitation displayed that GCβ3 could interact with the grass carp reovirus (GCRV) outer capsid protein VP5. Two incubation experiments revealed that the interaction of GCRV or VP5 proteins with GCβ3 could induce the expressions of type I interferons (IFNs) including IFN2 and IFN3 in grass carp ovary cell line. The functional analysis demonstrated that GCαvβ3 served as a receptor of viral protein components to be involved in antiviral immunity as human integrin αvβ3 did. In addition, both GCαv and GCβ3 were significantly upregulated in various tissues of grass carp after GCRV infection. This study might provide fundamental basis for understanding the molecular characteristics and immune functions of GCαvβ3, and offer a new insight into the antiviral immune mechanism specific to the integrins in grass carp.

The Early Immune Response of Lymphoid and Myeloid Head-Kidney Cells of Rainbow Trout (Oncorhynchus mykiss) Stimulated with Aeromonas salmonicida

The teleost head kidney is a highly relevant immune organ, and myeloid cells play a major role in this organ’s innate and adaptive immune responses. Because of their complexity, the early phases of the innate immune reaction of fish against bacteria are still poorly understood. In this study, naïve rainbow trout were stimulated with inactivated A. salmonicida and sampled at 12 h, 24 h and 7 d poststimulation. Cells from the head kidney were magnetically sorted with a monoclonal antibody mAB21 to obtain one (MAb21-positive) fraction enriched with myeloid cells and one (MAb21-negative) fraction enriched with lymphocytes and thrombocytes. The gene expression pattern of the resulting cell subpopulations was analysed using a panel of 43 immune-related genes. The results show an overall downregulation of the complement pathway and cytokine production at the considered time points. Some of the selected genes may be considered as parameters for diagnosing bacterial furunculosis of rainbow trout.

Molecular characterization and expression analysis of Japanese flounder (Paralichthys olivaceus) chemokine receptor CXCR2 in comparison with CXCR1

Chemokines are categorized into five families; one of the families is the CXC chemokines, which are critical in the pro-inflammatory process. CXC chemokines transmit signals and mediate a cell's biological activities by binding to cell surface receptors known as chemokine receptors (CXCRs). In this study, the CXCR2 from Japanese flounder (Paralichthys olivaceus) (JfCXCR2) was identified and characterized at the molecular level. The JfCXCR2 gene has a 1077 bp open reading frame that encodes a protein of 359 amino acid residues with seven transmembrane domains. Phylogenetic analysis of JfCXCR2 revealed that it belonged to the fish CXCR2 subfamily. Furthermore, JfCXCR2 was compared with the previously identified Japanese flounder CXCR1 (JfCXCR1). The expression analysis of uninfected Japanese flounder showed that JfCXCR1 and JfCXCR2 were expressed in all the tissues and organs tested but mainly in immune-related organs, including the kidney and spleen. Infection by Streptococcus iniae significantly increased the level of JfCXCR1 and JfCXCR2 mRNA in the kidney at days 1 and 3 post-infection. On the other hand, VHSV (viral hemorrhagic septicemia virus) and Edwardsiella tarda infection significantly increased JfCXCR2 mRNA levels in the kidney at days 3 and 6 post-infection, respectively. Conversely, JfCXCR1 expression was not significantly changed by either E. tarda or VHSV infection. Additionally, the peripheral blood leukocytes (PBLs) stimulated by recombinant proteins rCXCL8_L1a and rCXCL8_L1b were found to have significantly increased levels of JfCXCR1 and JfCXCR2 mRNA. Interestingly, even higher levels of JfCXCR1 and JfCXCR2 expression were observed in PBLs stimulated with rCXCL8_L1a and rCXCL8_L1b than in PBLs stimulated with either recombinant protein. These data suggest that bacterial infections may activate JfCXCR1. By contrast, JfCXCR2 may be activated by both bacterial and viral infection to mediate the immune response. These data can contribute to further understanding the functions of CXCR1 and CXCR2 in the fish immune system.