01和02型禽致病性大肠杆菌（APEC）是引起禽大肠杆菌病和禽产品污染的主要病原，为养禽业带来严重的经济损失。我们前期研究发现使用减毒沙门菌递呈大肠杆菌O1、O2多糖抗原时可诱导蛋鸡产生效果有别的同源免疫保护，具体原因未知。因此，本项目将通过生物化学和分子生物学等手段解析APEC O1和O2多糖抗原的分子结构和功能；通过基因突变、同源重组和细菌表型分析等工具阐明O-抗原多糖侧链影响细菌脂多糖图谱、定殖、黏附、运动、膜通透性和致病力等的分子机制；通过体液免疫应答、血清杀菌和细胞吞噬调理试验等探明O-抗原多糖侧链Man和Fuc介导的APEC O1免疫原性以及O1与O2交叉免疫保护机制；通过ELISPOT和流式细胞术等方法，解析O-抗原多糖侧链向CD4+、CD8+T细胞递呈抗原的作用机理。本研究对于揭示APEC多糖抗原侧链介导免疫原性差异的分子基础及建立对APEC的免疫防控策略具有重要意义。

The O1 and O2 group of avian pathogenic Escherichia coli (APEC) are the predominant causative agents of airsacculitis and colibacillosis, leading to significant economic loss in poultry industries due to serious poultry infection and pollution in food chains. Our previous studies showed that immune response against APEC O-antigen delivered by attenuated Salmonella could elicit protection against O1 and O2 pathogenic Escherichia coli challenge, while the protection efficacy against O1 was different to that elicited by O2. However, the underlying mechanisms remain largely unknown. In this study, the lipopolysaccharide structure and function of O1 and O2 group APEC will be investigated by biochemistry and molecular microbiology approaches. The lipopolysaccharide profiles, colonization, adhesion, mobility, membrane permeability and pathogenicity properties of O1 and O2 group APEC will be characterized by mutagenesis, homologous recombination and phenotype analysis tools. The immunogenicity and cross protection of Man- and Fuc- side chains of lipopolysaccharides toward O1 and O2 group APEC will be evaluated by humoral immunity, serum bactericidal, and phagocytosis assays. The presentation of O1 and O2 lipopolysaccharide to CD4+ and CD8+ T cells will be identified by ELISPOT assay and flow cytometry technique. This study will provide novel insights for better understanding of a novel molecular basis by which modulating O-antigen side chains to facilitate APEC immunity, which will be helpful for the prevention of APEC infection and reducing the incidence of disease in public health by implementing effective improvement strategies.