Department of Surgery, SUNY Upstate Medical University, Syracuse, New York, USA.
Department of Surgery, SUNY Upstate Medical University, Syracuse, New York, USA,
J Innate Immun. 2021;13(4):197-210. doi: 10.1159/000513605. Epub 2021 Feb 8.
Surfactant protein D (SP-D) is a C-type collectin and plays an important role in innate immunity and homeostasis in the lung. This study studied SP-D role in the nontypeable Haemophilus influenzae (NTHi)-induced otitis media (OM) mouse model. Wild-type C57BL/6 (WT) and SP-D knockout (KO) mice were used in this study. Mice were injected in the middle ear (ME) with 5 μL of NTHi bacterial solution (3.5 × 105 CFU/ear) or with the same volume of sterile saline (control). Mice were sacrificed at 3 time points, days 1, 3, and 7, after treatment. We found SP-D expression in the Eustachian tube (ET) and ME mucosa of WT mice but not in SP-D KO mice. After infection, SP-D KO mice showed more intense inflammatory changes evidenced by the increased mucosal thickness and inflammatory cell infiltration in the ME and ET compared to WT mice (p < 0.05). Increased bacterial colony-forming units and cytokine (IL-6 and IL-1β) levels in the ear washing fluid of infected SP-D KO mice were compared to infected WT mice. Molecular analysis revealed higher levels of NF-κB and NLRP3 activation in infected SP-D KO compared to WT mice (p < 0.05). In vitro studies demonstrated that SP-D significantly induced NTHi bacterial aggregation and enhanced bacterial phagocytosis by macrophages (p < 0.05). Furthermore, human ME epithelial cells showed a dose-dependent increased expression of NLRP3 and SP-D proteins after LPS treatment. We conclude that SP-D plays a critical role in innate immunity and disease resolution through enhancing host defense and regulating inflammatory NF-κB and NLRP3 activation in experimental OM mice.
表面活性蛋白 D（SP-D）是一种 C 型凝集素，在肺部的固有免疫和动态平衡中发挥重要作用。本研究探讨了 SP-D 在非分型流感嗜血杆菌（NTHi）诱导的中耳炎（OM）小鼠模型中的作用。本研究使用了野生型 C57BL/6（WT）和 SP-D 敲除（KO）小鼠。将 NTHi 细菌溶液（3.5×105 CFU/耳）或相同体积的无菌盐水（对照）5 μL 注射到中耳（ME）中。处理后第 1、3 和 7 天，处死小鼠。我们发现 WT 小鼠的咽鼓管（ET）和 ME 黏膜中有 SP-D 表达，但 SP-D KO 小鼠没有。感染后，与 WT 小鼠相比，SP-D KO 小鼠的 ME 和 ET 黏膜中的炎症变化更为剧烈，表现为黏膜厚度增加和炎症细胞浸润增加（p<0.05）。与感染 WT 小鼠相比，感染 SP-D KO 小鼠的耳洗液中的细菌菌落形成单位和细胞因子（IL-6 和 IL-1β）水平增加。分子分析显示，与 WT 小鼠相比，感染 SP-D KO 小鼠中的 NF-κB 和 NLRP3 激活水平更高（p<0.05）。体外研究表明，SP-D 可显著诱导 NTHi 细菌聚集，并增强巨噬细胞对细菌的吞噬作用（p<0.05）。此外，LPS 处理后，人 ME 上皮细胞中 NLRP3 和 SP-D 蛋白的表达呈剂量依赖性增加。综上所述，SP-D 通过增强宿主防御和调节炎症 NF-κB 和 NLRP3 激活，在实验性 OM 小鼠中发挥重要作用，从而在固有免疫和疾病缓解中发挥关键作用。
