The Relationship Between CD226 Molecule And Clinical Diseases And The Molecular Mechanisms

In 1985, Australian professor Burns G. immunized mice with activated lymphocytes in mixed lymphocyte culture(MLC) to prepare monoclonal antibody(mAb) of activated T cell surface antigen, then a molecule which could be specifically recognized and expressed on activated T cell surface membrane was screened out and named as LeoA1. Subsequently, molecule recognized by LeoA1 mAb was also found to be highly expressed on the surface of platelet, so this molecule was named as the platelet activation and T cell antigen 1(PTA1). In the 7th International Human Leukocyte Differentiation Antigen(HLDA7) Collaborative Group Congress in 2000, the anti-PTA1 mAb submitted by our lab and the anti-DNAM-1 mAb submitted by the DNAX institute were approved to obtain a new CD number-CD226, which is the first time to name a new CD mainly based on the studies of a Chinese lab.CD226 molecule is a member of the immunoglobulin superfamily(Ig SF),which contains two V-like domains in the extracellular region and the molecule weight is about 65 k D. CD226 molecule is mainly expressed in T cells, NK cells, NKT cells, megakaryocyte/platelet lineage, endothelial cells, the subtypes of B cell and some hematopoietic stem cells. In 2003, two ligands of human CD226 molecule were successfully identified, and they were human poliovirus receptor(PVR/CD155) and CD112. The interactions of CD226/CD226 Ls were involved in the differentiation and activation of T cells, the killing of tumor cells and virus-infected cells by NK cells, the adhesion of monocyte/macrophages to endothelial cells, the differentiation of macrophages and the activation and aggregation of platelets, etc. Moreover, interactions of CD226/CD226 Ls were closely related to some diseases, such as autoimmune diseases, graft-versus-host reactions and viral infections.Our previous studies found that CD226 mAb LeoA1 could regulate expression level of cytokines in human MLC system. Since MLC system is a multi-cell culture system and IL-10 is an immunosuppressive cytokine that could be synthesized and secreted by multiple immune cells(dendritic cells, macrophages, mast cells and NK cells, which were involved in innate immune response; Th1, Th2, Th17, Treg, CD8+ T cells and B cells, which were involved in adaptive immune response). It is absolutely necessary to find out the cellular mechanism of how CD226 molecule could influence the secretion of IL-10 in MLC system. What's more, as an important immunosuppressive cytokine, IL-10 modulates the strength of immune response in various stages and various sites of body immune response, thus participating in the onset and progress of many diseases. Therefore, the further studies about roles which CD226 and IL-10 play in clinical diseases will help us to deeply understand the functions of CD226. Given this, our studies have focused on CD226 and we have obtained the following results:(1) Based on the previous finding in our lab that CD226 mAb LeoA1 could regulate cytokine secretion in MLC systems, we observed the mechanisms of how LeoA1 could upregulate IL-10 expression. 24 hours after LeoA1 were added into MLC system, we found that the percentage of CD4+ IL-10+ T cells was significantly higher compared with control group, while the percentages of CD14+IL-10+ cell, CD19+IL-10+ cell, CD56+CD16+ IL-10+ cells, CD11c+HLA-DR+IL-10+ cells were not significantly different from control group, suggesting that LeoA1 might promote CD4+ IL-10+ T cell differentiation. In addition, we removed monocytes or CD4+ T cells or B cells from PBMC, respectively. Then we found that the expression level of IL-10 in MLC system could be significantly reduced after removing monocyte cells or CD4+ T cells from PBMC. It suggested that monocytes and CD4+ T cells might be involved in LeoA1 promoting the secretion of IL-10 in MLC system.(2) After EAE model with CD226 knockout mice and wild type mice were successfully established, we found that compared with wild type mice, the onset time of EAE delayed and the severity of EAE decreased in CD226 knockout mice. The HE staining of lumbar myeloid tissue showed that there were less inflammatory cells infiltrating in CD226 knockout mice at the peak period of EAE. ELISA showed that the serum expression levels of IL-10 in CD226 knockout mice higher than that in wild type mice at the peak period of EAE.(3) Blood samples of 120 lung cancer patients and 83 healthy volunteers were collected, then we extracted genomic DNA and examined the relationship between CD226 single nucleotide polymorphisms Gly307Ser(rs763361) and the risk of lung cancer by PCR-RFLP combined with statistical analysis. We found that in non-smoking group, the ratio of TT genotype is higher in lung cancer patients than that in healthy controls(OR=3.4846, 95%CI: 1.1932-10.1762, P=0.0224). In female group, there was no significant difference of TT genotype ratio between lung cancer patients(35.14%) and healthy controls(14.29%), but the P value is 0.0610, which suggesting CD226 rs763361 TT genotype may be associated with the susceptibility of women lung cancer.