Department of Ophthalmology, The Affiliated Hospital of Qingdao University, Qingdao, Shandong, China.
Infect Immun. 2024 Apr 9;92(4):e0048323. doi: 10.1128/iai.00483-23. Epub 2024 Mar 19.
() is one of the common pathogens of fungal keratitis. Fungal growth and invasion cause excessive inflammation and corneal damage, leading to severe vision loss. Neutrophils are the primary infiltrating cells critical for fungal clearance. Cathelicidin [LL-37 in humans and cathelicidin-related antimicrobial peptide (CRAMP) in mice], a natural antimicrobial peptide, can directly inhibit the growth of many pathogens and regulate immune responses. However, the role of cathelicidin and its effect on neutrophils in keratitis remain unclear. By establishing keratitis mouse models, we found that cathelicidin was increased in keratitis. It could reduce fungal loads, lower clinical scores, and improve corneal transparency. Restriction of CRAMP on fungal proliferation was largely counteracted in mice, in which neutrophils cannot migrate into infected sites. When WT neutrophils were transferred into mice, corneal fungal loads were distinctly reduced, indicating that neutrophils are vital for CRAMP-mediated resistance. Furthermore, cathelicidin promoted neutrophils to phagocytose and degrade conidia both and . CXC chemokine receptor 2 (CXCR2) was reported to be a functional receptor of LL-37 on neutrophils. CXCR2 antagonist SB225002 or phospholipase C (PLC) inhibitor U73122 weakened LL-37-induced phagocytosis. Meanwhile, LL-37 induced PLC γ phosphorylation, which was attenuated by SB225002. SB225002 or the autophagy inhibitors Bafilomycin-A1 and 3-Methyladenine weakened LL-37-induced degradation of conidia. Transmission electron microscopy (TEM) observed that LL-37 increased autophagosomes in -infected neutrophils. Consistently, LL-37 elevated autophagy-associated protein expressions (Beclin-1 and LC3-II), but this effect was weakened by SB225002. Collectively, cathelicidin reduces fungal loads and improves the prognosis of keratitis. Both and , cathelicidin promotes neutrophils to phagocytose and degrade conidia. LL-37/CXCR2 activates PLC γ to amplify neutrophils' phagocytosis and induces autophagy to eliminate intracellular conidia.
（）是真菌性角膜炎的常见病原体之一。真菌的生长和入侵会引起过度炎症和角膜损伤，导致严重的视力丧失。中性粒细胞是清除真菌的主要浸润细胞。抗菌肽（人源 LL-37 和鼠源抗菌肽相关肽（CRAMP））是一种天然抗菌肽，可直接抑制许多病原体的生长并调节免疫反应。然而，抗菌肽及其对真菌性角膜炎中性粒细胞的作用尚不清楚。通过建立真菌性角膜炎小鼠模型，我们发现抗菌肽在真菌性角膜炎中增加。它可以降低真菌负荷、降低临床评分并提高角膜透明度。在不能向感染部位迁移中性粒细胞的抗菌肽缺陷（）小鼠中，CRAMP 对真菌增殖的抑制作用在很大程度上被抵消。当 WT 中性粒细胞被转移到抗菌肽缺陷（）小鼠中时，角膜真菌负荷明显降低，表明中性粒细胞对 CRAMP 介导的抵抗至关重要。此外，抗菌肽促进中性粒细胞吞噬和降解分生孢子和。CXC 趋化因子受体 2（CXCR2）被报道为中性粒细胞上 LL-37 的功能受体。CXCR2 拮抗剂 SB225002 或磷脂酶 C（PLC）抑制剂 U73122 削弱了 LL-37 诱导的吞噬作用。同时，LL-37 诱导 PLCγ磷酸化，该磷酸化被 SB225002 减弱。SB225002 或自噬抑制剂巴弗洛霉素 A1 和 3-甲基腺嘌呤减弱了 LL-37 诱导的分生孢子降解。透射电子显微镜（TEM）观察到 LL-37 增加了感染中性粒细胞中的自噬体。一致地，LL-37 上调自噬相关蛋白表达（Beclin-1 和 LC3-II），但该作用被 SB225002 减弱。总之，抗菌肽降低真菌负荷并改善真菌性角膜炎的预后。和，抗菌肽促进中性粒细胞吞噬和降解分生孢子。LL-37/CXCR2 激活 PLCγ以放大中性粒细胞的吞噬作用，并诱导自噬以消除细胞内的分生孢子。
