AUTHOR=Liu Conghui , Yang Chuanyan , Wang Mengqiang , Jiang Shuai , Yi Qilin , Wang Weilin , Wang Lingling , Song Linsheng 

TITLE=A CD63 Homolog Specially Recruited to the Fungi-Contained Phagosomes Is Involved in the Cellular Immune Response of Oyster Crassostrea gigas

JOURNAL=Frontiers in Immunology

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2020.01379

DOI=10.3389/fimmu.2020.01379

ISSN=1664-3224

ABSTRACT=<p>Cluster of differentiation 63 (CD63), a four-transmembrane glycoprotein in the subfamily of tetraspanin, has been widely recognized as a gateway from the infection of foreign invaders to the immune defense of hosts. Its role in Pacific oyster <italic>Crassostrea gigas</italic> is, however, yet to be discovered. This work makes contributions by identifying <italic>Cg</italic>CD63H, a CD63 homolog with four transmembrane domains and one conservative CCG motif, and establishing its role as a receptor that participates in immune recognition and hemocyte phagocytosis. The presence of <italic>Cg</italic>CD63H messenger RNA (mRNA) in hepatopancreas, labial palps, gill, and hemocytes is confirmed. The expression level of mRNA in hemocytes is found significantly (<italic>p</italic> &lt; 0.01) upregulated after the injection of <italic>Vibrio splendidus</italic>. <italic>Cg</italic>CD63H protein, typically distributed over the plasma membrane of oyster hemocytes, is recruited to the <italic>Yarrowia lipolytica</italic>-containing phagosomes after the stimulation of <italic>Y. lipolytica</italic>. The recombinant <italic>Cg</italic>CD63H protein expresses binding capacity to glucan (GLU), peptidoglycan (PGN), and lipopolysaccharide (LPS) in the presence of lyophilized hemolymph. The phagocytic rate of hemocytes toward <italic>V. splendidus</italic> and <italic>Y. lipolytica</italic> is significantly inhibited (<italic>p</italic> &lt; 0.01) after incubation with anti-CgCD63H antibody. Our work further suggests that <italic>Cg</italic>CD63H functions as a receptor involved in the immune recognition and hemocyte phagocytosis against invading pathogen, which can be a marker candidate for the hemocyte typing in <italic>C. gigas</italic>.</p>