Department of Diagnostic Medicine/Pathobiology, Kansas State University College of Veterinary Medicine, Manhattan, KS, USA.
Department of Veterinary Basic Sciences, University of Nebraska-Lincoln, School of Veterinary Medicine and Biomedical Sciences, Lincoln, NE, USA.
Vet Microbiol. 2019 Mar;230:171-177. doi: 10.1016/j.vetmic.2019.02.015. Epub 2019 Feb 6.
K88 and F18 fimbrial enterotoxigenic Escherichia coli (ETEC) are the major causes of post-weaning diarrhea (PWD) in pigs. A vaccine that induces broad immunity to prevent K88 and F18 fimbrial ETEC bacterial attachment and colonization in pig small intestines and to neutralize enterotoxin enterotoxicity would be effective for PWD. Structure-based multiepitope-fusion-antigen (MEFA) technology using a backbone immunogen to present neutralizing epitopes of representing virulence factors capacitates development of broadly protective ETEC vaccines. Neutralizing epitopes have been identified from K88 fimbrial adhesin (FaeG) and enterotoxins but not F18 fimbrial adhesin. In this study, we in silico identified immunodominant epitopes from F18ac fimbrial subunit FedF which plays a critical role in F18 fimbrial adherence, genetically fused each epitope to a carrier, examined immunogenicity of each epitope fusion, and determined epitope-derived antibodies neutralizing activities against F18 fimbrial adherence. Data showed that seven immune-dominant epitopes were identified from FedF subunit. Fused to heterologous human ETEC adhesin subunit CfaB, epitope fusions induced anti-F18 antibodies in subcutaneously immunized mice. Moreover, antibodies derived from each fusion significantly blocked adherence of a F18-fimbrial E. coli bacteria to pig intestinal cell line IPEC-J2. While all seven epitopes exhibited neutralizing activity, results from this study identified FedF epitopes #3 (IPSSSGTLTCQAGT) and #7 (QPDATGSWYD) the most effective for antibodies against F18 fimbrial adherence, and suggested their future application in PWD vaccine development.
K88 和 F18 菌毛肠产毒性大肠杆菌（ETEC）是引起断奶后腹泻（PWD）的主要原因。一种能够诱导广泛免疫的疫苗，可以预防 K88 和 F18 菌毛 ETEC 细菌在猪小肠中的附着和定植，并中和肠毒素的肠毒性，将对 PWD 有效。基于结构的多表位融合抗原（MEFA）技术使用骨架免疫原来呈现代表毒力因子的中和表位，能够开发广泛保护的 ETEC 疫苗。已经从 K88 菌毛黏附素（FaeG）和肠毒素中鉴定出中和表位，但没有从 F18 菌毛黏附素中鉴定出。在这项研究中，我们通过计算机从在 F18 菌毛附着中起关键作用的 F18ac 菌毛亚基 FedF 中鉴定出免疫显性表位，将每个表位分别与载体基因融合，检测每个表位融合的免疫原性，并确定表位衍生的抗体对 F18 菌毛附着的中和活性。数据显示，从 FedF 亚基中鉴定出七个免疫显性表位。与异源人 ETEC 黏附素亚基 CfaB 融合后，融合蛋白在皮下免疫的小鼠中诱导出抗 F18 的抗体。此外，来自每个融合物的抗体显著阻止了 F18 菌毛大肠杆菌对猪肠细胞系 IPEC-J2 的附着。虽然这七个表位都显示出中和活性，但本研究的结果确定了 FedF 表位 #3（IPSSSGTLTCQAGT）和 #7（QPDATGSWYD）对抗体抗 F18 菌毛附着最有效，并提示它们在未来 PWD 疫苗开发中的应用。
