Table_6_Innovation in Nucleotide-Binding Oligomerization-Like Receptor and Toll-Like Receptor Sensing Drives the Major Histocompatibility Complex-II Free Atlantic Cod Immune System.xlsx

The absence of MHC class II antigen presentation and multiple pathogen recognition receptors in the Atlantic cod has not impaired its immune response however how underlying mechanisms have adapted remains largely unknown. In this study, ex vivo cod macrophages were challenged with various bacterial and viral microbe-associated molecular patterns (MAMP) to identify major response pathways. Cytosolic MAMP-PRR pathways based upon the NOD-like receptors (NLRs) and RIG-I-like receptors (RLRs) were identified as the critical response pathways. Our analyses suggest that internalization of exogenous ligands through scavenger receptors drives both pathways activating transcription factors like NF-kB (Nuclear factor-kappa B) and interferon regulatory factors (IRFs). Further, ligand-dependent differential expression of a unique TLR25 isoform and multiple NLR paralogues suggests (sub)neofunctionalization toward specific immune defensive strategies. Our results further demonstrate that the unique immune system of the Atlantic cod provides an unprecedented opportunity to explore the evolutionary history of PRR-based signaling in vertebrate immunity.

大西洋鳕（Atlantic cod）缺失主要组织相容性复合体II类（MHC class II）抗原呈递功能以及多种病原体识别受体（pathogen recognition receptors），却并未削弱其免疫应答，但其潜在的适应机制目前仍未完全阐明。本研究中，我们对离体大西洋鳕巨噬细胞施以多种细菌与病毒来源的微生物相关分子模式（microbe-associated molecular patterns，MAMP）刺激，以鉴定其主要的免疫应答通路。基于核苷酸结合寡聚化结构域样受体（NOD-like receptors，NLRs）与视黄酸诱导基因I样受体（RIG-I-like receptors，RLRs）的胞质MAMP-PRR通路被鉴定为关键的免疫应答通路。我们的分析显示，外源性配体通过清道夫受体（scavenger receptors）内化后，可激活上述两条通路，进而激活核因子-κB（NF-kB，Nuclear factor-kappa B）与干扰素调节因子（interferon regulatory factors，IRFs）等转录因子。此外，独特的Toll样受体25（TLR25）亚型与多种NLR旁系同源基因的配体依赖性差异表达，提示其发生了针对特异性免疫防御策略的（亚）新功能化（subneofunctionalization）。本研究结果进一步表明，大西洋鳕独特的免疫系统为探究脊椎动物免疫中基于PRR的信号通路的演化历史提供了前所未有的研究契机。