Dong Junjian, Wei Yuanzheng, Ye Xing, Sun Chengfei, Tian Yuanyuan, Lu Maixin, Du Juanjuan, Chen Zhihang
Key Laboratory of Tropical & Subtropical Fisheries Resource Application & Cultivation, Ministry of Agriculture, Pearl River Fisheries Institute, Chinese Academy of Fishery Sciences, Guangzhou 510380, China.
Key Laboratory of Tropical & Subtropical Fisheries Resource Application & Cultivation, Ministry of Agriculture, Pearl River Fisheries Institute, Chinese Academy of Fishery Sciences, Guangzhou 510380, China; College of Fisheries and Life Science, Shanghai Ocean University, Shanghai 201306, China.
Mol Immunol. 2016 May;73:158-69. doi: 10.1016/j.molimm.2016.01.005. Epub 2016 Feb 1.
Sialic acid - binding immunoglobulin - like lectins (Siglecs) are members of the largest superfamily of immune receptors; they recognize sialic acid and are mainly expressed in immune cells. Studies on mammals indicate that Streptococcus agalactiae (GBS) evade immune reactions by interacting with the host immune cells via the sialic acid of sialylated capsular polysaccharides. However, it is currently unknown if fish-derived GBS can interact with Siglecs to evade host immunity. In this study, we examined the binding of FITC-GBS with neutrophils to determine the presence of receptors that binds with GBS. Furthermore, 3 Siglec-like genes, (OnSiglec-1-like/-4b-like/-14-like) from the neutrophils cDNA were screened by PCR. All the genes had specific domains (immunostimulation and immunosuppression domains), conserved amino acid residues, and sialic acid polysaccharide binding sites that are found in mammalian Siglecs. Flow cytometry of Siglecs-like/COS-7 cells and ELISA of Siglecs/Ex-Fc fusion proteins confirmed that 3 Siglecs-like have high binding activity with GBS. Erythrocytes adhesion assays and sialylated glycans binding assay confirmed that 3 Siglecs-like bind to sialic acid polysaccharides. Siglecs-like had high expression levels in the spleen, gill, and kidney in Oreochromis niloticus by qPCR. After experimental infection, Siglec-1-like/-14-like showed a significant upregulated initially and later downregulated in liver, spleen, kidney, and gill. However, Siglec-4b-like was downregulated in most tissues, except that in liver. The results indicate that 3 OnSiglecs-like may recognize GBS sialylated capsular polysaccharides. GBS infections led to significant changes in Siglecs-like expression in immune-related tissues. However, immunostimulation or immunosuppression via the recognition of GBS by different Siglecs-like molecules requires additional studies.
唾液酸结合免疫球蛋白样凝集素（Siglecs）是最大的免疫受体超家族成员；它们识别唾液酸，主要在免疫细胞中表达。对哺乳动物的研究表明，无乳链球菌（GBS）通过唾液酸化荚膜多糖的唾液酸与宿主免疫细胞相互作用来逃避免疫反应。然而，目前尚不清楚鱼类来源的GBS是否能与Siglecs相互作用以逃避宿主免疫。在本研究中，我们检测了异硫氰酸荧光素标记的GBS（FITC-GBS）与中性粒细胞的结合，以确定与GBS结合的受体的存在。此外，通过聚合酶链反应（PCR）从嗜中性粒细胞cDNA中筛选出3个类Siglec基因（OnSiglec-1-like/-4b-like/-14-like）。所有这些基因都具有特定结构域（免疫刺激和免疫抑制结构域）、保守氨基酸残基以及在哺乳动物Siglecs中发现的唾液酸多糖结合位点。类Siglec/COS-7细胞的流式细胞术和Siglec/Ex-Fc融合蛋白的酶联免疫吸附测定（ELISA）证实，3种类Siglec与GBS具有高结合活性。红细胞黏附试验和唾液酸化聚糖结合试验证实，3种类Siglec与唾液酸多糖结合。通过实时定量聚合酶链反应（qPCR）检测发现，类Siglec在尼罗罗非鱼的脾脏、鳃和肾脏中表达水平较高。实验感染后，类Siglec-1-like/-14-like在肝脏、脾脏、肾脏和鳃中最初显著上调，随后下调。然而，类Siglec-4b-like在大多数组织中下调，肝脏除外。结果表明，3种OnSiglec类蛋白可能识别GBS唾液酸化荚膜多糖。GBS感染导致免疫相关组织中类Siglec表达发生显著变化。然而，不同类Siglec分子通过识别GBS进行免疫刺激或免疫抑制还需要进一步研究。
