The Study On The Correlations Of Gene Polymorphisms And Expression Levels Of PD-1 And CTLA-4 With Susceptibility To Human Diseases And Immune Functions

Immunoglobulin superfamily (IgSF) is a huge family of proteins, members of which have great similarity with immunoglobulin (Ig) in structure. Programmed death-1 (PD-1) and cytotoxic T-lymphocyte associated antigen 4 (CTLA-4), two important members of IgSF, are pivotal immune regulatory molecules in human. Numerous studies have demonstrated that PD-1 and CTLA-4 inhibit T cell activation and proliferation and they play crucial role in autoimmune diseases and cancers. To date, the majority of the explicit pathogeneses of human diseases remain obscure. It is generally accepted that disease results from complex interactions between genetic and environmental factors. Only a fraction of people exposured to the similar environment ultimately fall ill, suggesting an important role of individual genetic predisposition in disease. It is reported by Human Genome Project (HGP) that there are 99.9% identical in the human genome between individuals and only tiny genetic differences in sequence, i.e., genetic polymorphism, the most important of which is single nucleotide polymorphisms (SNPs). SNPs serve as genetic markers to explore diseases genetic risk factors, which becomes a new strategy to investigate the complicated etiology of diseases involving tumor. Both esophageal cancer and cervical cancer are the most frequently diagnosed cancer. Hashimoto's thyroiditis (HT) is a common autoimmune thyroid disorders. We performed the study to evaluate the correlation of PD-1 expression levels and PD-1 tagSNPs with susceptibility to esophageal squamous cell carcinoma (ESCC) in Chinese patients and proportions of Treg and Breg, in combination with the clinical and pathologic data from patients. Additionally, we assessed the association of CTLA-4 polymorphism with HT and cervical cancer. Four parts of this study are as follows:Part one:PD-1 tagSNPs genotyping was performed in 629 ESCC cases and 686 controls. A significantly decreased risk of ESCC associated with PD-1 rs 10204525 A>G polymorphism was overt among male and younger patients. No significant association of PD-1 tagSNPs rs7421861T>C and rs2227982C>T with ESCC risk was detected. Our results demonstrate for the first time that the PD-1 rs 10204525 polymorphism might contribute to susceptibility of ESCC.Part two:Both PD-1 expression on CD4+T cells and the percentage of Tregs were significantly higher in ESCC patients than in controls. The level of PD-1 expression on CD4+T cells from ESCC patients is positively correlated with the percentage of Tregs. Increased percentage of Tregs was significantly correlated with the PD-1 rs 10204525 AG genotype. The PD-1 expression levels in tumor tissues are significantly associated with histopathological differentiated grade, clinical stage and lymph node metastasis. These results suggest that the elevated percentage of Tregs may result from the presence of the PD-1 rs 10204525 G polymorphism. Also, the results suggest that the increased expression of PD-1 in tumor tissues may be related to the progression of ESCC. No significant differences in PD-1 expression levels on CD8+T and CD19+ B cells emerged between cases and controls. A significantly lower percentage of PD-1+CD14+ monocytes was observed in cases compared with controls. The percentage of Bregs in ESCC cases was marginally higher than that in controls. No associations of the level of PD-1 expression on immune cells as well as the percentage of Tregs and Bregs with clinical and pathology parameters were observed. Therefore, we speculate that PD-1 rs10204525 might affect the immune function of ESCC patients and facilate immune evasion in cancer, leading to cell malignant change and contributing to carcinogenesis.Part three:CTLA-4 rs231775A>G polymorphism was significantly associated with the increased risk of HT. The analysis by ethnicity groups clearly indicated that this association is stronger in the Asian population than that in the Caucasian population, suggesting that the association may be ethnicity-specific.Part four:Asian populations had a reduced risk of cervical cancer for the CTLA-4 +49A/G polymorphism, but an increased risk for the CTLA-4 -318C/T polymorphism, indicating that CTLA-4 +49A/G polymorphism and CTLA-4 -318C/T polymorphism may be associated with the risk of cervical cancer and the associations may be ethnicity-specific. The results may provide support for an important role of CTLA-4 in human malignant diseases, which is of far-reaching significance.