FGL1/SLAII-LAG3通路介导PRRS持续性感染的作用机制

淋巴组织持续性病毒感染是PRRS的主要特征之一，其机制尚未完全阐明。宿主细胞共抑制分子表达上调是持续性感染形成的重要机制，淋巴细胞活化基因3(LAG3)是与MHCⅡ相关的共抑制分子，纤维蛋白原样蛋白1(FGL1)是其主要配体，FGL1或MHCⅡ与LAG3结合能负调T细胞增殖与功能，造成抗原清除减少。我们前期研究发现，PRRSV感染猪淋巴组织LAG3转录显著升高，因此推测PRRSV感染上调T细胞LAG3表达，借助FGL1/SLAⅡ-LAG3通路抑制T细胞增殖与功能，导致病毒清除减少引起持续性感染。本项目拟确定PRRSV感染猪不同组织FGL1、SLAⅡ和LAG3表达上调后，利用siRNA干扰、过表达、LAG3抗体阻断或FGL1蛋白处理明确调控LAG3影响PRRSV复制，再通过体内外抗体阻断和效应细胞功能和细胞因子检测等，从激活FGL1/SLAⅡ-LAG3通路的角度解析PRRS持续性感染形成的机制。

Persistent viral infection of lymphoid tissues is one major characteristics of PRRS, and the mechanism has not been fully elucidated. Lots of studies indicated that up-regulation of coinhibitory molecules on host cells is one of the crucial mechanisms leading to persistent viral infection. Lymphocyte activation gene 3(LAG3) is an important coinhibitory molecule which is closely related to MHC class II molecule(MHCII), and frinogen-like protein 1(FGL1) is a major immune inhibitory ligand of LAG3 newly discovered. The interaction of FGL1 or MHCII with LAG3 can negatively regulate the proliferation and function of T lymphocytes, thus decreasing virus elimination. The results from our previous studies showed that PRRSV infection led to significantly increasing of LAG3 transcription in pig thymus, spleen, lymph node, etc. Base on our results and these research advances, we speculate that PRRSV infection raises LAG3 expression, activates FGL1/SLAII-LAG3 pathways and inhibits proliferation and function of T cell, which results in decrease of virus removal and persistent infection. In this project, up-regulated expression of FGL1, SLAII and LAG3 in different tissues of infected pig is firstly determined using molecular biology and immunological techniques. Then PRRSV replication affected by regulation LAG3 expression is confirmed by siRNA interference, overexpression, blocking by specific Ab against LAG3, or treatment with FGL1. By downstream cell function and cytokines detection after Ab blocking in vivo and in vitro, we want to elucidate the mechanism of persistent PRRSV infection from the angle of activation FGL1/SLAII-LAG3 pathway. The results can accumulate data for the research of PRRS pathogenesis.