AUTHOR=Ning Mingxiao , Xiu Yunji , Yuan Meijun , Bi Jingxiu , Hou Libo , Gu Wei , Wang Wen , Meng Qingguo 

TITLE=Spiroplasma eriocheiris Invasion Into Macrobrachium rosenbergii Hemocytes Is Mediated by Pathogen Enolase and Host Lipopolysaccharide and β-1, 3-Glucan Binding Protein

JOURNAL=Frontiers in Immunology

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2019.01852

DOI=10.3389/fimmu.2019.01852

ISSN=1664-3224

ABSTRACT=<p><italic>Spiroplasma eriocheiris</italic> is a crustacean pathogen, without a cell wall, that causes enormous economic loss. <italic>Macrobrachium rosenbergii</italic> hemocytes are the major targets during <italic>S. eriocheiris</italic> infection. As wall-less bacteria, <italic>S. eriocheiris</italic>, its membrane protein should interact with host membrane protein directly and firstly when invaded in host cell. In this investigation, six potential hemocyte receptor proteins were identified firstly that mediate interaction between <italic>S. eriocheiris</italic> and <italic>M. rosenbergii</italic>. Among these proteins, lipopolysaccharide and β-1, 3-glucan binding protein (MrLGBP) demonstrated to bind to <italic>S. eriocheiris</italic> using bacterial binding assays and confocal microscopy. Four spiroplasma ligand proteins for MrLGBP were isolated and identified. But, competitive assessment demonstrated that only enolase of <italic>S. eriocheiris</italic> (SeEnolase) could be a candidate ligand for MrLGBP. Subsequently, the interaction between MrLGBP and SeEnolase was confirmed by co-immunoprecipitation and co-localization <italic>in vitro</italic>. After the interaction between MrLGBP and SeEnolase was inhibited by antibody neutralization test, the virulence ability of <italic>S. eriocheiris</italic> was effectively reduced. The quantity of <italic>S. eriocheiris</italic> decreased in <italic>Drosophila</italic> S2 cells after overexpression of <italic>MrLGBP</italic>, compared with the controls. In addition, RNA interference (RNAi) knockdown of <italic>MrLGBP</italic> made <italic>M. rosenbergii</italic> more sensitive to <italic>S. eriocheiris</italic> infection. Further studies found that the immune genes, including <italic>MrLGBP</italic> and <italic>prophenoloxidase</italic> (<italic>MrproPO</italic>), <italic>MrRab7A</italic>, and <italic>Mrintegrin</italic> α<italic>1</italic> were significantly up-regulated by SeEnolase stimulation. After SeEnolase pre-stimulation, the ability of <italic>M. rosenbergii</italic> resistance to <italic>S. eriocheiris</italic> was significantly improved. Collectively, this investigation demonstrated that MrLGBP and pathogen SeEnolase involved in mediating <italic>S. eriocheiris</italic> invasion into <italic>M. rosenbergii</italic> hemocytes.</p>