| Summary: | 碩士 === 國立成功大學 === 微生物及免疫學研究所 === 95 === Lewis b antigen (Leb) is a surface structure expressed on the gastric epithelium and interacts with blood group antigen-binding adhesin (BabA) of H. pylori, thus contributing to H. pylori adherence. Recently, sialyl-Lewis x antigen (sLex) has been found to be expressed on gastric epithelium during chronic inflammation induced by H. pylori and serves as a receptor for sialic acid-binding adhesin (SabA) of H. pylori. In patients who express no gastric Lewis b or weak Leb, the interaction between sLex and SabA increases the H. pylori colonization density. sLex is a member of Lewis histo-blood group antigen family and its biosynthesis is regulated by ��2,3-sialyltransferases (ST3Gal) and ��1,3-fucosyltransferases (FUT). Our aims of this study were to investigate whether and how H. pylori can trigger the sLex expression on gastric epithelium. In order to address these issues, we established a cell line model. We found that human gastric epithelial cell line MKN45 cells cocultured with H. pylori directly did not have detectable sLex antigen expression on cell surface. However, cells treated with H. pylori-infected cell filtrates or
H. pylori culture filtrates continued to increase sLex expression up to 48 h. By comparing the percentages of increased expression of sLex, we observed that cells treated with H. pylori culture filtrates consistently has 17% lower expression of sLex as compared to those treated with H. pylori-infected cell filtrates. These observations suggest that besides bacterial components secreted in the culture filtrates, factors released by cells in response to H. pylori infection are also involved in the up-regulation of sLex expression, although the former plays a predominant role. In this cell line model, sLex expression could not be induced to express on gastric epithelial cell line by recombinant human TNF-�� or IL-8 or their combination.
In contrast, certain virulence factors, such as CagA, VacA and BabA, they all participate in the up-regulation of sLex expression. This was shown by the fact that CagA, VacA, or BabA isogenic mutants all have reduced ability to induce sLex expression when compared to wild type. RT-PCR and real-time RT-PCR analysis indicated that enhanced expression of ST3Gal III and FUT III, V, VI and VII mRNA were observed in cells with increased sLex expression due to treatment with culture filtrates. ST3Gal III promoter reporter gene analysis indicated that -123 to -90 bp upstream of transcriptional start site may harbor positive regulatory elements involved in the up-regulation of sLex expression. FUT III promoter reporter gene analysis indicated that positive regulatory elements may be located within -149 to +32 bp region of FUT III gene or further downstream. In summary,
H. pylori can induce sLex expression on gastric epithelial cells and the ST3Gal III as well as FUT III, V, VI and VII genes are associated with the up-regulation of sLex
expression.
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