Toll样受体基因多态性与幽门螺杆菌感染、非贲门胃癌发病风险的关系

It is well accepted that gastric cancer is a complex, multifactorial disease. Helicobacter pylori (H. pylori) has been classified as a definite carcinogen for the stomach by the World Health Organization. Innate immune plays an important role in H. pylori-induced chronic inflammation and gastric cancer. Toll-like receptors are important members of the host's innate immune response, being involved in recognition of bacteria, regulation of inflammatory reactions and activation of the subsequent adaptive immune response. The normal gastric epithelial cells show specific expression of TLR2, TLR4, TLR5, and TLR9. Some studies indicate that TLR2, TLR4, TLR5, and TLR9 genes may be involved in the infection of H. pylori and the development of gastric cancer. In the present study, we will evaluate the relationships between the polymorphisms in the TLR2, TLR4, TLR5, and TLR9 genes and H. pylori infection, or non-cardia gastric cancer risk, using a tagging SNP approach in a case-control study, which is going to recruit 500 cases with non-cardia gastric cancer and 500 normal controls in Baotou Han population. The study would provide experimental data and theoretical basis for prevention, gene therapy, and new drug development of gastric cancer. Furthermore, we will estimate the effects of the interactions between polymorphisms and environmental factors on the risk of non-cardia gastric cancer.

胃癌是复杂的多基因疾病，其中幽门螺杆菌已被世界卫生组织确定为胃的I类致癌原。在幽门螺杆菌引起的慢性炎症以及胃癌的病变过程中，非特异性免疫应答起到了重要的作用。Toll样受体（TLRs）在非特异性免疫中扮演了重要的角色，可以识别细菌、调控炎症反应以及激活后续的特异性免疫应答。胃中特异性地表达TLR2、TLR4、TLR5和TLR9。研究提示这四种基因可能参与了幽门螺杆菌感染和胃癌的发生。本研究拟在包头汉族人群中征集500例非贲门胃癌病人和500例正常对照，用病例-对照关联研究的方法，采用全面广泛的标记单核苷酸多态性（Tag-SNPs）途径检测TLR2、TLR4、TLR5和TLR9基因多态性与幽门螺杆菌感染、非贲门胃癌发病风险的关系，为胃癌预防措施的制订以及基因治疗、开发新药积累实验参考和理论依据。此外，我们还将探讨所检测的基因多态性与环境因素的相互作用对非贲门胃癌的影响。

本研究在包头地区汉族人群中收集了289例非贲门胃癌病人和282例正常对照，正常对照和胃癌病人在性别、年龄方面相匹配。用酶联免疫吸附法（ELISA）在正常对照中检测了幽门螺杆菌的感染情况，发现阳性率为43.3%，且幽门螺杆菌的感染与性别、年龄没有关联。根据HapMap数据库（http://hapmap.ncbi.nlm.nih.gov）中中国人的数据，使用Agorithm-Tagger-pairwise Tagging软件筛选了TLR5和TLR9基因的tagSNPs，筛选范围包括基因第一个外显子上游20 kb和最后一个外显子下游10 kb的序列，筛选过程中使用的参数为LD r2 > 0.8 和最小等位基因频率（MAF）> 5%。在所有样本中对筛选到的11个tagSNPs进行了基因分型。结果显示TLR5和TLR9基因多态性可能与幽门螺杆菌感染关联；但与非贲门胃癌的发病风险没有关联。此外，各SNP位点之间的相互作用在幽门螺杆菌感染以及非贲门胃癌的发病风险中无统计学意义。总之，本项目顺利完成了原计划的研究内容，为胃癌预防措施的制订以及基因治疗、开发新药积累了一定的实验参考和理论依据。