Avian Pathogenic Escherichia coli (APEC) poses a significant threat to the U.S. poultry industry, causing respiratory infections and systemic colibacillosis. Understanding APEC's impact on the immune response is crucial for developing effective prevention and treatment strategies. This study investigates the dynamic immune responses to APEC infection in broiler chickens, with a focus on survival rates, airsac lesion scores, and cytokine gene expression patterns in lung tissue. Seven-day-old broiler chicks were divided into control and APEC-inoculated groups, with the control group receiving tryptic soy broth and the APEC group receiving 7 × 10^{^7} CFU of APEC via intratracheal inoculation. Survival data included both male and female birds, while airsac lesion score and lung tissue samples for gene expression analyses were collected only from male birds at nine time points post-infection (days 1, 3, 5, 7, 9, 11, 13, 15, and 21). High airsac lesion incidence and mortality were observed during early infection stages, decreasing in mid to later stages as anti-inflammatory cytokines were upregulated. The lung gene expression study analyzed the expression of pro-inflammatory cytokines (IFN-γ, IL-1β, IL-8, and IL-6), regulator (SOCS3), and anti-inflammatory cytokines (IL-10, TGFβ-2, TGFβ-3, and IL-1RN) via RT-qPCR assays, using 18S rRNA for normalization. A two-way ANOVA followed by Tukey's Kramer test evaluated the effects of APEC treatment and days post-infection on gene expression, with the Mann-Whitney U test comparing fold changes between groups. Results indicated an early upregulation of pro-inflammatory cytokines like IFN-γ and IL-1β, followed by the modulatory roles of SOCS3, TGF-β, and IL-1RN, balancing the immune response and possibly preventing excessive tissue damage. This study elucidates the dynamic regulation of key cytokines during APEC infection in chickens, providing insights into immune mechanisms. Understanding these mechanisms is crucial for developing targeted therapies and improving disease management in poultry, potentially reducing antibiotic dependence and enhancing overall poultry health and productivity.

Keywords: Avian pathogenic Escherichia coli; Broiler chicken; Cytokine; Gene expression; Immune response.

Copyright © 2025. Published by Elsevier Inc.

禽病原性大肠杆菌（APEC）对美国家禽产业构成重大威胁，会导致呼吸系统感染和全身性coli败血症。了解APEC对免疫反应的影响对于开发有效的预防和治疗策略至关重要。本研究探讨了APEC感染对肉鸡动态免疫反应的影响，重点关注生存率、气囊病变评分以及肺组织中细胞因子基因表达模式的变化。7日龄的肉鸡被分为对照组和APEC接种组，对照组接受胰蛋白酶大豆 broth 处理，而APEC组通过支气管内接种7 × 10^{^7} CFU 的 APEC 进行处理。生存数据包括雄性和雌性鸟类的数据，而在九个不同的感染后时间点（第1、3、5、7、9、11、13、15和21天）仅从雄性鸟类收集气囊病变评分和肺组织样本用于基因表达分析。在早期感染阶段观察到高气囊病变发病率和死亡率，随着抗炎细胞因子的上调，在中期至后期这些指标下降。肺部基因表达研究通过实时定量 PCR (RT-qPCR) 实验分析了促炎细胞因子（IFN-γ、IL-1β、IL-8 和 IL-6）、调节因子(SOCS3)和抗炎细胞因子(IL-10、TGFβ-2、TGFβ-3 和 IL-1RN) 的表达，使用 18S rRNA 进行标准化。采用双向方差分析（two-way ANOVA）结合Tukey's Kramer 检验评估 APEC 处理和感染后天数对基因表达的影响，并通过 Mann-Whitney U 检验比较各组间的倍变化差异。结果表明，在早期促炎细胞因子如 IFN-γ 和 IL-1β 上调，随后 SOCS3、TGF-β 和 IL-1RN 的调节作用平衡了免疫反应并可能防止过度组织损伤。本研究阐明了APEC感染期间鸡体内关键细胞因子的动态调控机制，为了解免疫机制提供了见解。理解这些机制对于开发靶向疗法和改善家禽疾病管理至关重要，这有可能减少抗生素依赖，并提高整体家禽健康和生产效率。

关键词： 禽病原性大肠杆菌；肉鸡；细胞因子；基因表达；免疫反应。