Interleukin 4 induces rapid mucin transport, increases mucus thickness and quality and decreases colitis and <i>Citrobacter rodentium</i> in contact with epithelial cells

<i>Citrobacter rodentium</i> infection is a murine model for pathogenic intestinal <i>Escherichia coli</i> infection. <i>C. rodentium</i> infection causes an initial decrease in mucus layer thickness, followed by an increase during clearance. We aimed to identify the cause of these changes and to utilize this naturally occurring mucus stimulus to decrease pathogen impact and inflammation. We identified that mucin production and speed of transport from Golgi to secretory vesicles at the apical surface increased concomitantly with increased mucus thickness. Of the cytokines differentially expressed during increased mucus thickness, IFN-γ and TNF-α decreased the mucin production and transport speed, whereas IL-4, IL-13, <i>C. rodentium</i> and <i>E. coli</i> enhanced these aspects. IFN-γ and TNF-α treatment in combination with <i>C. rodentium</i> and pathogenic <i>E. coli</i> infection negatively affected mucus parameters <i>in vitro</i>, which was relieved by IL-4 treatment. The effect of IL-4 was more pronounced than that of IL-13, and in wild type mice, only IL-4 was present. Increased expression of <i>Il-4, Il-4-receptor α, Stat6</i> and <i>Spdef</i> during clearance indicate that this pathway contributes to the increase in mucin production. <i>In vivo</i> IL-4 administration initiated 10 days after infection increased mucus thickness and quality and decreased colitis and pathogen contact with the epithelium. Thus, during clearance of infection, the concomitant increase in IL-4 protects and maintains goblet cell function against the increasing levels of TNF-α and IFN-γ. Furthermore, IL-4 affects intestinal mucus production, pathogen contact with the epithelium and colitis. IL-4 treatment may thus have therapeutic benefits for mucosal healing.鼠柠檬酸杆菌（Citrobacter rodentium）感染是肠致病性大肠杆菌（Escherichia coli）感染的小鼠模型。鼠柠檬酸杆菌感染会引发黏液层厚度的初始下降，随后在病原体清除阶段出现厚度回升。本研究旨在阐明此类黏液层变化的成因，并利用这种自然发生的黏液刺激效应，以降低病原体的致病影响与炎症反应。我们发现，黏蛋白的生成速率以及其从高尔基体转运至顶膜分泌囊泡的速度，会随黏液层厚度增加而同步提升。在黏液层厚度增加过程中差异表达的细胞因子中，干扰素-γ（IFN-γ）与肿瘤坏死因子-α（TNF-α）会抑制黏蛋白生成及转运速率；而白细胞介素-4（IL-4）、白细胞介素-13（IL-13）、鼠柠檬酸杆菌以及致病性大肠杆菌则可增强上述过程。在联合施加IFN-γ与TNF-α，并结合鼠柠檬酸杆菌及致病性大肠杆菌感染的体外实验中，黏液相关参数出现了负面改变，而IL-4处理可缓解这一不良影响。IL-4的调控效果较IL-13更为显著，且在野生型小鼠体内仅能检测到IL-4的表达。在病原体清除阶段，Il-4、Il-4-receptor α、Stat6及Spdef的表达上调，表明该信号通路参与了黏蛋白生成的增强过程。在感染10天后启动的IL-4体内给药，可提升黏液层厚度与质量，并减轻结肠炎症状及病原体与上皮细胞的接触程度。因此，在感染清除阶段，IL-4水平的同步升高可对抗逐渐升高的TNF-α与IFN-γ水平，从而保护并维持杯状细胞功能。此外，IL-4可影响肠道黏液生成、病原体与上皮细胞的接触以及结肠炎的发生发展。综上，IL-4治疗或许可为黏膜愈合提供治疗益处。