Phongsisay Vongsavanh, Iizasa Ei'ichi, Hara Hiromitsu, Yamasaki Sho
Division of Molecular Immunology, Medical Institute of Bioregulation, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan.
Division of Molecular and Cellular Immunoscience, Department of Biomolecular Sciences, Faculty of Medicine, Saga University, Saga, Japan.
Mol Immunol. 2014 Nov;62(1):169-77. doi: 10.1016/j.molimm.2014.06.012. Epub 2014 Jul 5.
LMIR5/CD300b is an activating immunoglobulin-like receptor whose extracellular domain (LMIR5-Fc) is constitutively released from immune cells. The release of LMIR5-Fc is augmented upon stimulation with TLR agonists. LMIR5-Fc is reported to possess inflammatory activity and amplify LPS-induced lethal inflammation; however, its action mechanism has not been clarified. This study was aimed to identify receptors for LMIR5-Fc. Using NF-κB reporter cells in human monocytes THP1, LMIR5-Fc was solely found to trigger NF-κB activation among various signaling receptors examined. In addition, an injection of LMIR5-Fc into the mouse peritoneal resulted in a rapid production of inflammatory mediators and an amplification of LPS activity. Moreover, LMIR5-Fc-induced cytokine production was markedly reduced in TLR4-deficient mouse macrophages. Using TLR4 reporter cells, the LMIR5-Fc sample that contained a trace amount of endotoxin under the sensitivity of reporter cells triggered a potent NF-κB activation. Furthermore, the inflammatory activity of LMIR5-Fc was completely lost by heating but unchanged by polymyxin B pretreatment. Using TLR4 fusion protein, TLR4 was found to interact specifically with LMIR5-overexpressing cells. Therefore, LMIR5-Fc is new inflammatory mediator and endogenous ligand of TLR4. This study provides an insight into the positive feedback mechanism of inflammation through TLR4-LMIR5-Fc axis.
LMIR5/CD300b是一种激活型免疫球蛋白样受体，其细胞外结构域（LMIR5-Fc）可从免疫细胞中持续释放。用TLR激动剂刺激后，LMIR5-Fc的释放会增加。据报道，LMIR5-Fc具有炎症活性并能放大LPS诱导的致死性炎症；然而，其作用机制尚未阐明。本研究旨在鉴定LMIR5-Fc的受体。在人单核细胞THP1中使用NF-κB报告细胞，在检测的各种信号受体中，仅发现LMIR5-Fc能触发NF-κB激活。此外，向小鼠腹腔注射LMIR5-Fc会导致炎症介质迅速产生并放大LPS活性。此外，在TLR4缺陷的小鼠巨噬细胞中，LMIR5-Fc诱导的细胞因子产生明显减少。使用TLR4报告细胞，在报告细胞敏感范围内含有微量内毒素的LMIR5-Fc样品可触发强烈的NF-κB激活。此外，LMIR5-Fc的炎症活性通过加热完全丧失，但多粘菌素B预处理对其无影响。使用TLR4融合蛋白，发现TLR4与过表达LMIR5的细胞特异性相互作用。因此，LMIR5-Fc是一种新的炎症介质和TLR4的内源性配体。本研究为通过TLR4-LMIR5-Fc轴的炎症正反馈机制提供了见解。
