The major role of chemokines is to act as a chemoattractant to guide the migration of immune cells to the infectious sites. In the current study, we found that CiCXCL20a, a teleost-specific chemokine from grass carp (Ctenopharyngodon idella), demonstrates broad-spectrum, potent, direct bactericidal activity and immunomodulatory functions to bacterial infections, apart from the chemotaxis. CiCXCL20a kills bacteria by binding, mainly targeting acid lipids, perforating bacterial membrane, resulting in bacterial cytoplasm leakage and death. CiCXCL20a aggregates and neutralizes LPS, agglutinates Gram-negative bacteria, and binds to peptidoglycan and Gram-positive bacteria, but not agglutinate them. All the complexes may be phagocytized and cleared away. CiCXCL20a chemoattracts leukocytes, facilitates phagocytosis of myeloid leukocytes, not lymphoid leukocytes, and enhances the bacteria-killing ability in leukocytes. We further identified its receptor CiCXCR3.1b1. Furthermore, we investigated the physiological roles of CiCXCL20a against Aeromonas hydrophila infection in vivo. The recombinant CiCXCL20a increases the survival rate and decreases the tissue bacterial loads, edema, and lesions. Then, we verified this function by purified CiCXCL20a Ab blockade, and the survival rate decreases, and the tissue bacterial burdens increase. In addition, zebrafish (Danio rerio) DrCXCL20, an ortholog of CiCXCL20a, was employed to verify the bactericidal function and mechanism. The results indicated that DrCXCL20 also possesses wide-spectrum, direct bactericidal activity through membrane rupture mechanism. The present study, to our knowledge, provides the first evidence that early vertebrate chemokine prevents from bacterial infections by direct bactericidal and phagocytosis-killing–promoting manners. The results also demonstrate the close functional relationship between chemokines and antimicrobial peptides.

趋化因子的主要作用是作为一种化学引诱物，引导免疫细胞迁移到感染部位。在目前的研究中，我们发现 CiCXCL20a，一种来自草鱼 ( Ctenopharyngodon idella)，除了趋化性外，还对细菌感染具有广谱、有效、直接的杀菌活性和免疫调节功能。CiCXCL20a通过结合杀死细菌，主要靶向酸性脂质，穿透细菌膜，导致细菌细胞质渗漏而死亡。CiCXCL20a 聚集和中和 LPS，凝集革兰氏阴性菌，并与肽聚糖和革兰氏阳性菌结合，但不凝集它们。所有的复合物都可以被吞噬和清除。CiCXCL20a 化学吸引白细胞，促进髓性白细胞（而非淋巴样白细胞）的吞噬作用，并增强白细胞的杀菌能力。我们进一步鉴定了其受体 CiCXCR3.1b1。此外，我们研究了 CiCXCL20a 对嗜水气单胞菌的生理作用体内感染。重组 CiCXCL20a 提高了存活率并减少了组织细菌负荷、水肿和病变。然后，我们通过纯化的 CiCXCL20a Ab 阻断验证了该功能，存活率降低，组织细菌负担增加。此外，斑马鱼 ( Danio rerio) DrCXCL20，CiCXCL20a 的直系同源物，用于验证杀菌功能和机制。结果表明，DrCXCL20还通过破膜机制具有广谱、直接的杀菌活性。据我们所知，本研究提供了第一个证据，表明早期脊椎动物趋化因子通过直接杀菌和促进吞噬作用的方式预防细菌感染。结果还证明了趋化因子和抗菌肽之间的密切功能关系。