Department of Aquatic Animal Medicine, College of Fisheries, Huazhong Agricultural University, Wuhan, China.
Hubei Provincial Engineering Laboratory for Pond Aquaculture, Hubei Engineering Technology Research Center for Aquatic Animal Disease Control and Prevention, Wuhan, China.
Front Immunol. 2021 Aug 2;12:686846. doi: 10.3389/fimmu.2021.686846. eCollection 2021.
Chitooligosaccharide (COS) is an important immune enhancer and has been proven to have a variety of biological activities. Our previous research has established an M1 polarization mode by COS in blunt snout bream () macrophages, but the mechanism of COS activation of blunt snout bream macrophages remains unclear. In this study, we further explored the internalization mechanism and signal transduction pathway of chitooligosaccharide hexamer (COS6) in blunt snout bream macrophages. The results showed that mannose receptor C-type lectin-like domain 4-8 of (MaMR CTLD4-8) could recognize and bind to COS6 and mediate COS6 into macrophages by both clathrin-dependent and caveolin-dependent pathways. In the inflammatory response of macrophages activated by COS6, the gene expression of tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and nitric oxide synthase 2 (NOS2) was significantly inhibited after MaMR CTLD4-8-specific antibody blockade. However, even if it was blocked, the expression of these inflammation-related genes was still relatively upregulated, which suggested that there are other receptors involved in immune regulation. Further studies indicated that MaMR CTLD4-8 and Toll-like receptor 4 (TLR4) cooperated to regulate the pro-inflammatory response of macrophages caused by COS6. Taken together, these results revealed that mannose receptor (MR) CTLD4-8 is indispensable in the process of recognition, binding, internalization, and immunoregulation of COS in macrophages of blunt snout bream.
壳寡糖（COS）是一种重要的免疫增强剂，已被证明具有多种生物学活性。我们之前的研究通过壳寡糖使草鱼（）巨噬细胞产生了 M1 极化模式，但壳寡糖激活草鱼巨噬细胞的机制仍不清楚。在本研究中，我们进一步探讨了壳寡糖六聚体（COS6）在草鱼巨噬细胞中的内化机制和信号转导途径。结果表明，（MaMR）CTLD4-8 能够识别和结合 COS6，并通过网格蛋白依赖和胞饮作用途径介导 COS6 进入巨噬细胞。在 COS6 激活的巨噬细胞炎症反应中，MaMR CTLD4-8 特异性抗体阻断后，肿瘤坏死因子（TNF）-α、白细胞介素（IL）-1β 和一氧化氮合酶 2（NOS2）的基因表达显著受到抑制。然而，即使进行了阻断，这些炎症相关基因的表达仍然相对上调，这表明还有其他受体参与免疫调节。进一步的研究表明，MaMR CTLD4-8 和 Toll 样受体 4（TLR4）协同调节 COS6 引起的巨噬细胞的促炎反应。综上所述，这些结果表明，甘露糖受体（MR）CTLD4-8 在草鱼巨噬细胞识别、结合、内化和免疫调节 COS 的过程中是不可或缺的。
