新生犊牛小肠上皮受体介导IgG转运通路的研究

Morbidity rates in neonatal calves were approximately at 30% in the literature. These calves has negatively related to the early growth and long-term calf performance, which is critical to the survival and health of dairy industry. Neonatal calves must intake the immunoglobulin G (IgG) from colostrum that are important for contributing to passive immunity acquisition. Up to date, several studies indicated that enterocyte IgG uptake in the small intestine of neonatal calves were selected during the period of passive immunity acquisition. However, the receptor of IgG and its mediated transport pathways in the small intestine of neonatal calves have not yet completely elucidated. Thus, the objective of this study is to investigate the receptor and transport pathways of IgG in the small intestine of neonatal calves based on the proteomics, immunohistochemical and bioinformatics approaches. These contents are included the selection the receptor of IgG, and identification proteins related to the IgG and transport pathway for IgG in the small intestine that used to explore the receptor-mediated transport pathways for IgG in the small intestine of neonatal calves. These results can be useful for gaining the receptor of IgG transport in the small intestine and proteins related to the IgG transport in neonatal calves, and further for improving the IgG absorption in the small intestine of neonatal calves contributed to passive immunity acquisition.

新生犊牛发病率高达30%，导致患病犊牛早期生长发育减缓和后期生产性能下降，对奶业的健康发展威胁很大。新生犊牛小肠从初乳中摄取足够量的IgG进入外周血是实现免疫保护的关键。目前，已有研究表明新生犊牛小肠摄取初乳中IgG存在选择性，但是关于小肠上皮选择性摄取IgG所需的受体及IgG转运通路还不十分清楚。因此，本项目拟采用蛋白质组学和免疫组化技术以及生物信息学分析等策略，开展新生犊牛小肠上皮IgG受体筛选及IgG转运相关通路的研究，包括小肠上皮IgG识别受体的筛选、小肠上皮摄取IgG相关蛋白的鉴定及相关通路分析。本项目研究结果为进一步确定小肠上皮IgG受体蛋白及转运通路提供试验基础，以及调控新生犊牛小肠转运IgG的效率及提高被动免疫的成功率提供科学依据。

因母源免疫球蛋白不能通过胎盘屏障进入胎牛循环，因此，新生犊牛必须从初乳中摄取足够的免疫球蛋白建立被动免疫是保障其生存及健康成长的关键。目前，虽然有许多研究揭示了初乳中IgG进入犊牛血液循环的表观吸收率，但新生犊牛选择性吸收初乳中IgG及转运通路仍缺乏清晰的阐释。因此，本项目以新生犊牛为研究对象，设立对照组（不饲喂），初乳组I、II和III（饲喂初乳）以及常乳组（饲喂常乳），采集犊牛血清和肠组织样品等用免疫共沉淀、免疫组化和蛋白质组学及生物信息学等技术探究犊牛肠上皮选择性吸收初乳中IgG的受体及转运通路。结果表明初乳经新生犊牛肠道吸收后IgG含量显著下降，相应的肠组织中转运囊泡和IgG含量也下降，而新生犊牛血清中IgG含量随初乳饲喂则显著增加；犊牛血清及代谢物的表达变化发现初乳中大分子仅IgG呈显著增加，表明新生犊牛肠上皮存在IgG识别受体而选择性吸收初乳中IgG进入血液循环；肠组织差异蛋白组研究发现，饲喂初乳后肠上皮摄入的初乳IgG含量显著增加，同时锌α2糖蛋白、多聚免疫球蛋白受体、Ras相关蛋白7A、β2巨球蛋白（B2M）和网格蛋白重链1等表达量增加，而其他主要乳蛋白则先增加后下降，而饲喂常乳犊牛肠上皮中没有检测到IgG。比较分析后初步确定犊牛肠上皮表达的B2M和新生动物FC受体α链（FCGRT）是选择性吸收初乳IgG的识别受体；此外，将牛B2M和FCGRT基因在真核细胞内表达并与牛IgG共培养也表明了其与IgG的结合特性；生物信息学分析预测了新生犊牛肠上皮受体B2M和FCGRT介导初乳中IgG的转运通路。本项目研究结果为进一步验证肠上皮IgG受体及转运通路提供了实验基础；还可为科学有效的调节犊牛摄取初乳中IgG效率成功建立被动免疫以及促进犊牛培育提供了依据。