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Front. Immunol. | doi: 10.3389/fimmu.2018.02758

A Novel Lipopolysaccharide Recognition Mechanism Mediated by Internalization in Teleost Macrophages

 Xinjiang Lu1, 2*, Yingjun Ning1, He Liu1,  Li Nie1, 2 and  Jiong Chen1, 2*
  • 1Ningbo University, China
  • 2Key Laboratory of Applied Marine Biotechnology, Ministry of Education, Ningbo University, China

Macrophages in teleosts are less sensitive to lipopolysaccharide (LPS) compared to mammals. The functional equivalent of the mammalian LPS surface receptor in teleost macrophages for the pro-inflammatory response is either non-existent or replaced by negative regulation. LPS signaling in teleost macrophages remains unclear. Here, we found a scavenger receptor class B 2a (PaSRB2a) that played a crucial role in LPS signaling in teleost macrophages. The internalization of LPS and subsequent pro-inflammatory responses in macrophages were mediated by PaSRB2a, which is a novel isoform of the mammalian SRB2 gene. LPS internalization by PaSRB2a is dependent on its C-terminal intracellular domain. Following LPS internalization, it interacts with the ayu intracellular receptors nucleotide-binding oligomerization domain protein 1 (PaNOD1) and PaNOD2. Moreover, LPS pre-stimulation with sub-threshold concentrations reduced the effect of secondary LPS treatment on pro-inflammatory responses that were mediated by PaSRB2a. The pro-inflammatory responses in LPS-treated ayu were down-regulated upon PaSRB2a knockdown by lentivirus siRNA delivery. In grass carp and spotted green pufferfish, SRB2a also mediated LPS internalization and pro-inflammatory responses. Our work identifies a novel LPS signaling pathway in teleosts that differs from those in mammals, and contributes to the understanding of the evolution of pathogen recognition in vertebrates.

Keywords: teleost, Macrophages, lipopolysaccharide, Scavenger receptor class B2, Inflammation

Received: 27 Aug 2018; Accepted: 09 Nov 2018.

Edited by:

Geert Wiegertjes, Wageningen University & Research, Netherlands

Reviewed by:

Magdalena Chadzińska, Jagiellonian University, Poland
Hai-peng Liu, Xiamen University, China  

Copyright: © 2018 Lu, Ning, Liu, Nie and Chen. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence:
Prof. Xinjiang Lu, Ningbo University, Ningbo, China, lxj711043@163.com
Prof. Jiong Chen, Ningbo University, Ningbo, China, jchen1975@163.com