AUTHOR=Liu Wenjing , Xing Jing , Tang Xiaoqian , Sheng Xiuzhen , Chi Heng , Zhan Wenbin 

TITLE=Characterization of Co-Stimulatory Ligand CD80/86 and Its Effect as a Molecular Adjuvant on DNA Vaccine Against Vibrio anguillarum in Flounder (Paralichthys olivaceus)

JOURNAL=Frontiers in Immunology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2022.881753

DOI=10.3389/fimmu.2022.881753

ISSN=1664-3224

ABSTRACT=<p>The CD80/86 molecule is one of the important co-stimulatory ligands and involves antigen-specific immune responses by ligating with CD28 and then delivering the required second signal to T-cell activation. In this study, a CD80/86 homolog was identified, and its expression characteristics were studied in flounder (<italic>Paralichthys olivaceus</italic>). The open reading frame (ORF) of <italic>CD80/86</italic> is 906 bp, encoding 301 aa, and the extracellular amino acid sequence encoded two IgV- and IgC-like structural domains; <italic>fCD80/86</italic> is highly expressed in head kidney, peripheral blood leukocytes (PBLs), and spleen, and has relatively high expression in muscle. Antibodies specific for CD80/86 were produced, and CD80/86 was colocalized with MHCII+, CD40+, and CD83+ leukocytes but not with IgM+, CD3+, or CD4+ lymphocytes. The cloned CD80/86 in flounder shares conserved structural features with its mammalian counterparts and is mainly distributed on antigen-presenting cells. Based on these data, CD80/86 as an adjuvant to enhance the immune response of DNA vaccine was investigated. A bicistronic DNA vaccine expressing both CD80/86 and the outer membrane protein (OmpK) of <italic>Vibrio anguillarum</italic> (p-OmpK-CD80/86) was successfully constructed. After immunization, p-OmpK-CD80/86 could induce the upregulation of the proportion of IgM+ and CD4+ cells in flounder, compared to the p-OmpK- or p-CD80/86-immunized group; <italic>CD28</italic> genes were significantly induced in the p-CD80/86 and p-OmpK-CD80/86 groups. Compared to the p-OmpK group, the higher expression of <italic>CD83</italic>, <italic>MHCI</italic>, <italic>CD4</italic>, <italic>CD8</italic>, and <italic>IL-2</italic> was detected at the injection site. The relative percent survival (RPS) produced by p-OmpK-CD80/86 is 66.11% following the <italic>V. anguillarum</italic> challenge, while the RPS of p-OmpK or p-CD80/86 is 46.30% and 5.56%, respectively. The results revealed that CD80/86 is mainly found in antigen-presenting cells, and could help elicit humoral immune responses in teleost through the CD80/86-CD28 signaling pathway involving CD4+ lymphocytes.</p>